Mauna Loa ( or ; Hawaiian: ; en, Long Mountain) is one of five volcanoes that form the

Island of Hawaii Hawaii ( ; haw, Hawaii ) is the largest island in the United States, located in the state of Hawaii. It is the southeasternmost of the Hawaiian Islands, a chain of volcanic islands in the North Pacific Ocean. With an area of , it has 63% of th ...

in the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sover ...

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

. The largest subaerial volcano (as opposed to subaqueous volcanoes) in both mass and volume, Mauna Loa has historically been considered the largest volcano on

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, dwarfed only by

Tamu Massif Tamu Massif is a seamount in the northwest Pacific Ocean, sitting atop a triple junction of mid-ocean ridges. Tamu Massif is located in the

It is an

active Active may refer to: Music * ''Active'' (album), a 1992 album by Casiopea * Active Records, a record label Ships * ''Active'' (ship), several commercial ships by that name * HMS ''Active'', the name of various ships of the British Royal ...

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...

with relatively gentle slopes, with a volume estimated at , although its peak is about lower than that of its neighbor,

Mauna Kea Mauna Kea ( or ; ; abbreviation for ''Mauna a Wākea''); is a dormant volcano on the island of Hawaii. Its peak is above sea level, making it the highest point in the state of Hawaii and second-highest peak of an island on Earth. The peak is ...

. Lava eruptions from Mauna Loa are

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

-poor and very fluid, and tend to be non-explosive. Mauna Loa has probably been erupting for at least 700,000 years, and may have emerged above sea level about 400,000 years ago. The oldest-known dated rocks are not older than 200,000 years. The volcano's

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

comes from the

Hawaii hotspot The Hawaii hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the best known and intensively studied hotspots in the world, the Hawaii plume is responsible for the creation of the ...

, which has been responsible for the creation of the Hawaiian island chain over tens of millions of years. The slow

drift Drift or Drifts may refer to: Geography * Drift or ford (crossing) of a river * Drift, Kentucky, unincorporated community in the United States * In Cornwall, England: ** Drift, Cornwall, village ** Drift Reservoir, associated with the village ...

of the

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

will eventually carry Mauna Loa away from the hotspot within 500,000 to one million years from now, at which point it will become extinct. Mauna Loa's most recent eruption began on November 27, 2022 and ended on December 13th. It was the first eruption since

1984 Events January * January 1 – The Bornean Sultanate of Brunei gains full independence from the United Kingdom, having become a British protectorate in 1888. * January 7 – Brunei becomes the sixth member of the Association of Southeast A ...

. No recent eruptions of the volcano have caused fatalities, but eruptions in 1926 and 1950 destroyed villages, and the city of

Hilo Hilo () is a census-designated place (CDP) and the largest settlement in Hawaii County, Hawaii, Hawaii County, Hawaii, United States, which encompasses the Hawaii (island), Island of Hawaii. The population was 44,186 according to the 2020 United ...

is partly built on lava flows from the late 19th century. Because of the potential hazards it poses to population centers, Mauna Loa is part of the

Decade Volcanoes The Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) as being worthy of particular study in light of their history of large, destructive volcanic eruption, ...

program, which encourages studies of the world's most dangerous volcanoes. Mauna Loa has been monitored intensively by the

Hawaiian Volcano Observatory The Hawaiian Volcano Observatory (HVO) is an agency of the U.S. Geological Survey (USGS) and one of five volcano observatories operating under the USGS Volcano Hazards Program. Based in Hilo, Hawaii, the observatory monitors six Hawaiian volcanoe ...

since 1912. Observations of the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

are undertaken at the

Mauna Loa Observatory The Mauna Loa Observatory (MLO) is an atmospheric baseline station on Mauna Loa, on the island of Hawaii, located in the U.S. state of Hawaii. The observatory Since 1958, initially under the direction of Charles Keeling, followed by his s ...

, and of the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

at the

Mauna Loa Solar Observatory Mauna Loa Solar Observatory (MLSO) is a solar observatory located on the slopes of Mauna Loa on the island of Hawaii in the U.S. state of Hawaii. It is operated by the High Altitude Observatory (HAO), a laboratory within the National Center for A ...

, both located near the mountain's summit.

Hawaii Volcanoes National Park Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...

covers the summit and portions of the southeastern and southwestern flanks of the volcano, and also incorporates

Kīlauea Kīlauea ( , ) is an active shield volcano in the Hawaiian Islands. Located along the southeastern shore of the Big Island of Hawaii, the volcano is between 210,000 and 280,000 years old and emerged above sea level about 100,000 years ago. Hi ...

, a separate volcano.

Geology

Setting

Like all Hawaiian volcanoes, Mauna Loa was created as the

Pacific tectonic plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

moved over the

in the Earth's underlying mantle. The Hawaii island volcanoes are the most recent evidence of this process that, over 70 million years, has created the -long

Hawaiian–Emperor seamount chain The Hawaiian–Emperor seamount chain is a mostly undersea mountain range in the Pacific Ocean that reaches above sea level in Hawaii. It is composed of the Hawaiian ridge, consisting of the islands of the Hawaiian chain northwest to Kure Atoll, ...

. The prevailing view states that the hotspot has been largely stationary within the planet's mantle for much, if not all of the

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

Era. However, while the Hawaiian

mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hot ...

is well understood and extensively studied, the nature of hotspots themselves remains fairly enigmatic. Mauna Loa is one of five subaerial volcanoes that make up the island of

Hawaiʻi Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...

. The oldest volcano on the island, Kohala, is more than a million years old, and

, the youngest, is believed to be between 210,000 and 280,000 years of age. Kamaʻehuakanaloa (formerly Lōʻihi) on the island's flank is even younger, but has yet to breach the surface of the Pacific Ocean. At 1 million to 600,000 years of age, Mauna Loa is the second youngest of the five volcanoes on the island, making it the

third Third or 3rd may refer to: Numbers * 3rd, the ordinal form of the cardinal number 3 * , a fraction of one third * Second#Sexagesimal divisions of calendar time and day, 1⁄60 of a ''second'', or 1⁄3600 of a ''minute'' Places * 3rd Street (d ...

youngest volcano in the

Hawaiian – Emperor seamount chain Hawaiian may refer to: * Native Hawaiians, the current term for the indigenous people of the Hawaiian Islands or their descendants * Hawaii state residents, regardless of ancestry (only used outside of Hawaii) * Hawaiian language Historic uses * ...

, a chain of

es and

seamount A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...

s extending from

to the

Kuril–Kamchatka Trench The Kuril–Kamchatka Trench or Kuril Trench (russian: Курило-Камчатский жёлоб, ''Kurilo-Kamchatskii Zhyolob'') is an oceanic trench in the northwest Pacific Ocean. It lies off the southeast coast of Kamchatka and parallels ...

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

. Following the

pattern A pattern is a regularity in the world, in human-made design, or in abstract ideas. As such, the elements of a pattern repeat in a predictable manner. A geometric pattern is a kind of pattern formed of geometric shapes and typically repeated l ...

of Hawaiian volcano formation, Mauna Loa would have started as a

submarine volcano Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. Many submarine volcanoes are located near areas of tectonic plate formation, known as mid-ocean ridges. The volcanoes at mid-ocean ridges ...

, gradually building itself up through underwater eruptions of

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

before emerging from the sea through a series of

surtseyan eruption A Surtseyan eruption is an explosive style of volcanic eruption that takes place in shallow seas or lakes when rapidly rising and fragmenting hot magma interacts explosively with water and with water-steam-tephra slurries. The eruption style is ...

s about 400,000 years ago. Since then, the volcano has remained active, with a history of effusive and

explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...

eruptions, including 34 eruptions since the first well-documented eruption in 1843.

Structure

Mauna Loa is the largest subaerial and second largest overall volcano in the world (behind

Tamu Massif Tamu Massif is a seamount in the northwest Pacific Ocean, sitting atop a triple junction of mid-ocean ridges. Tamu Massif is located in the

covering a land area of and spans a maximum width of . Consisting of approximately of solid rock, it makes up more than half of the surface area of the island of Hawaiʻi. Combining the volcano's extensive submarine flanks ( to the sea floor) and subaerial height, Mauna Loa rises from base to summit, greater than the elevation of

Mount Everest Mount Everest (; Tibetan: ''Chomolungma'' ; ) is Earth's highest mountain above sea level, located in the Mahalangur Himal sub-range of the Himalayas. The China–Nepal border runs across its summit point. Its elevation (snow heig ...

from sea level to its summit. In addition, much of the mountain is invisible even underwater: its mass depresses the crust beneath it by another , in the shape of an inverse mountain, meaning the total height of Mauna Loa from the start of its eruptive history is about . Mauna Loa summit in snow 2016

Mauna Loa is a typical

in form, taking the shape of a long, broad dome extending down to the ocean floor whose

slopes In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...

are about 12° at their steepest, a consequence of its extremely

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

lava. The shield-stage lavas that built the enormous main mass of the mountain are

tholeiitic basalt The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma i ...

s, like those of

, created through the mixing of primary

and

subducted Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

oceanic crust. Mauna Loa's summit hosts three overlapping

pit crater A pit crater (also called a subsidence crater or collapse crater) is a depression formed by a sinking or collapse of the surface lying above a void or empty chamber, rather than by the eruption of a volcano or lava vent. Pit craters are found ...

s arranged northeast–southwest, the first and last roughly in diameter and the second an oblong feature; together these three craters make up the summit caldera Mokuʻāweoweo, so named for the Hawaiian ʻāweoweo fish (''

Priacanthus meeki ''Priacanthus meeki'' is a species of marine ray finned fish, a bigeye in the family Priacanthidae. It is a red fish found in the Hawaiian and Midway Islands. It grows to a size of 33 cm in length. Common names are Hawaiian bigeye in Englis ...

''), purportedly due to the resemblance of its eruptive fires to the coloration of the fish. Mokuʻāweoweo's caldera floor lies between beneath its rim and it is only the latest of several calderas that have formed and reformed over the volcano's life. It was created between 1,000 and 1,500 years ago by a large eruption from Mauna Loa's northeast rift zone, which emptied out a shallow

magma chamber A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it upw ...

beneath the summit and collapsed it into its present form. Additionally, two smaller pit craters lie southwest of the caldera, named Lua Hou (New Pit) and Lua Hohonu (Deep Pit). Mauna Loa's summit is also the focal point for its two prominent

rift zone A rift zone is a feature of some volcanoes, especially shield volcanoes, in which a set of linear cracks (or rifts) develops in a volcanic edifice, typically forming into two or three well-defined regions along the flanks of the vent. Believed t ...

s, marked on the surface by well-preserved, relatively recent lava flows (easily seen in satellite imagery) and linearly arranged fracture lines intersected by

cinder Cinder is an alternate term for scoria. Cinder or Cinders may also refer to: In computing *Cinder (programming library), a C++ programming library for visualization *Cinder, OpenStack's block storage component * Cyber Insider Threat, CINDER, a ...

and

splatter cone Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and s ...

s. These rift zones are deeply set structures, driven by

dike Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...

intrusions along a decollement fault that is believed to reach down all the way to the volcano's base, deep. The first is a rift trending southwest from the caldera to the sea and a further underwater, with a prominent 40° directional change along its length; this rift zone is historically active across most of its length. The second, northeastern rift zone extends towards

and is historically active across only the first of its length, with a nearly straight and, in its latter sections, poorly defined trend. The northeastern rift zone takes the form of a succession of cinder cones, the most prominent of which the high Puu Ulaula, or Red Hill. There is also a less definite northward rift zone that extends towards the Humuula Saddle marking the intersection of Mauna Loa and Mauna Kea. Simplified geophysical models of Mauna Loa's

have been constructed, using

interferometric synthetic aperture radar Interferometric synthetic aperture radar, abbreviated InSAR (or deprecated IfSAR), is a radar technique used in geodesy and remote sensing. This geodetic method uses two or more synthetic aperture radar (SAR) radar imaging, images to generate maps o ...

measures of

ground deformation Ground may refer to: Geology * Land, the surface of the Earth not covered by water * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical c ...

due to the slow buildup of lava under the volcano's surface. These models predict a wide magma chamber located at a depth of about , below

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...

, near the southeastern margin of Mokuʻāweoweo. This shallow magma chamber is significantly higher-placed than Mauna Loa's rift zones, suggesting magma

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s into the deeper parts and occasional dike injections into the shallower parts of the rift zone drive rift activity; a similar mechanism has been proposed for neighboring

. Earlier models based on Mauna Loa's two most recent eruptions made a similar prediction, placing the chamber at deep in roughly the same geographic position. Mauna Loa has complex interactions with its neighbors,

Hualālai Hualālai (pronounced in Hawaiian) is an active volcano on the island of Hawaii in the Hawaiian Islands. It is the westernmost, third-youngest and the third-most active of the five volcanoes that form the island of Hawaii, following Kīlauea a ...

to the northwest,

to the northeast, and particularly

to the east. Lavas from Mauna Kea intersect with Mauna Loa's basal flows as a consequence of Kea's older age, and Mauna Kea's original

s were buried beneath post-shield volcanic rocks of Mauna Loa; additionally, Mauna Kea shares Mauna Loa's gravity well, depressing the ocean crust beneath it by . There are also a series of

normal fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

s on Mauna Loa's northern and western slopes, between its two major rift zones, that are believed to be the result of combined circumferential tension from the two rift zones and from added pressure due to the westward growth of neighboring Kīlauea. Because Kīlauea lacks a

topographical prominence In topography, prominence (also referred to as autonomous height, relative height, and shoulder drop in US English, and drop or relative height in British English) measures the height of a mountain or hill's summit relative to the lowest contou ...

and appears as a bulge on the southeastern flank of Mauna Loa, it was historically interpreted by both native Hawaiians and early geologists to be an active satellite of Mauna Loa. However, analysis of the chemical composition of lavas from the two volcanoes show that they have separate

s, and are thus distinct. Nonetheless, their proximity has led to a historical trend in which high activity at one volcano roughly coincides with low activity at the other. When Kīlauea lay dormant between 1934 and 1952, Mauna Loa became active, and when the latter remained quiet from 1952 to 1974, the reverse was true. This is not always the case; the

1984 eruption of Mauna Loa The 1984 eruption of Mauna Loa was a Hawaiian eruption in the U.S. state of Hawaii that lasted from March 25 to April 15, 1984. It ended a 9-year period of quiescence at the volcano and continued for 22 days, during which time lava flows and lava ...

started during an eruption at Kīlauea, but had no discernible effect on the Kīlauea eruption, and the ongoing inflation of Mauna Loa's summit, indicative of a future eruption, began the same day as new lava flows at Kīlauea's

Puʻu ʻŌʻō Puu Ōō (also spelled Pu‘u‘ō‘ō, and often written Puu Oo, , ) is a volcanic cone on the eastern rift zone of Kīlauea volcano in the Hawaiian Islands. The eruption that created Puu Ōō began on January 3, 1983, and continued nearly con ...

crater. Geologists have suggested that "pulses" of magma entering Mauna Loa's deeper magma system may have increased pressure inside Kīlauea and triggered the concurrent eruptions. Mauna Loa is slumping eastward along its southwestern rift zone, leveraging its mass into Kīlauea and driving the latter eastward at a rate of about per year; the interaction between the two volcanoes in this manner has generated a number of large earthquakes in the past, and has resulted in a significant area of debris off Kīlauea's seaward flank known as the

Hilina Slump The Hilina Slump, on the south flank of the Kīlauea Volcano on the southeast coast of the Big Island of Hawaiʻi, is the most notable of several landslides that ring each of the Hawaiian Islands. These landslides are the means by which materia ...

. A system of older faults exists on the southeastern side of Mauna Loa that likely formed before Kilauea became large enough to impede Mauna Loa's slump, the lowest and northernmost of which, the Kaoiki fault, remains an active earthquake center today. The west side of Mauna Loa, meanwhile, is unimpeded in movement, and indeed is believed to have undergone a massive slump collapse between 100,000 and 200,000 years ago, the residue from which, consisting of a scattering of debris up to several kilometers wide and up to distant, is still visible today. The damage was so extensive that the headwall of the damage likely intersected its southwestern rift zone. There is very little movement there today, a consequence of the volcano's geometry. Mauna Loa taken from the 9300 ft level on the ascent of Mauna Kea

Mauna Loa taken from the 9300 ft level on the ascent of Mauna Kea

Mauna Loa is tall enough to have experienced

glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...

during the last ice age, 25,000 to 15,000 years ago. Unlike Mauna Kea, on which extensive evidence of glaciation remains even today, Mauna Loa was at the time and has remained active, having grown an additional in height since then and covering any glacial deposits beneath new flows; strata of that age don't occur until at least down from the volcano's summit, too low for glacial growth. Mauna Loa also lacks its neighbor's summit

permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface ...

region, although sporadic ice persists in places. It is speculated that extensive

phreatomagmatic Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions cont ...

activity occurred during this time, contributing extensively to

ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...

deposits on the summit.

Eruptive history

Prehistoric eruptions

To have reached its enormous size within its relatively short (geologically speaking) 600,000 to 1,000,000 years of life, Mauna Loa would logically have had to have grown extremely rapidly through its developmental history, and extensive

charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, cal ...

-based

radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was dev ...

(perhaps the most extensive such prehistorical eruptive dating on Earth) has amassed a record of almost two hundred reliably dated extant flows confirming this hypothesis. The oldest exposed flows on Mauna Loa are thought to be the Ninole Hills on its southern flank, subaerial

rock dating back approximately 100 to 200 thousand years. They form a terrace against which younger flows have since banked, heavily eroded and incised against its slope in terms of direction; this is believed to be the result of a period of erosion because of a change in the direction of lava flow caused by the volcano's prehistoric slump. These are followed by two units of lava flows separated by an intervening

layer known as the Pāhala ash layer: the older Kahuka basalt, sparsely exposed on the lower southwest rift, and the younger and far more widespread Kaʻu basalt, which appear more widely on the volcano. The Pāhala ashes themselves were produced over a long period of time circa 13 to 30 thousand years ago, although heavy

vitrification Vitrification (from Latin ''vitreum'', "glass" via French ''vitrifier'') is the full or partial transformation of a substance into a glass, that is to say, a non-crystalline amorphous solid. Glasses differ from liquids structurally and glasses po ...

and interactions with post- and pre- creation flows has hindered exact dating. Their age roughly corresponds to the glaciation of Mauna Loa during the last ice age, raising the distinct possibility that it is the product of

interaction between the long-gone glaciers and Mauna Loa's eruptive activities. Studies have shown that a cycle occurs in which volcanic activity at the summit is dominant for several hundred years, after which activity shifts to the rift zones for several more centuries, and then back to the summit again. Two cycles have been clearly identified, each lasting 1,500–2,000 years. This cyclical behavior is unique to Mauna Loa among the Hawaiian volcanoes. Between about 7,000 and 6,000 years ago Mauna Loa was largely inactive. The cause of this cessation in activity is not known, and no known similar hiatus has been found at other Hawaiian volcanoes except for those currently in the post-shield stage. Between 11,000 and 8,000 years ago, activity was more intense than it is today. However, Mauna Loa's overall rate of growth has probably begun to slow over the last 100,000 years, and the volcano may in fact be nearing the end of its

shield-building phase.

Recent history

Ancient Hawaii Ancient Hawaii is the period of Hawaiian history preceding the unification in 1810 of the Kingdom of Hawaii by Kamehameha the Great. Traditionally, researchers estimated the first settlement of the Hawaiian islands as having occurred sporadicall ...

ans have been present on Hawaiʻi island for about 1,500 years, but they preserved almost no records on volcanic activity on the island, beyond a few fragmentary accounts dating to the late 18th and early 19th centuries. Possible eruptions occurred around 1730 and 1750 and sometime during 1780 and 1803. A June 1832 eruption was witnessed by a missionary on

Maui The island of Maui (; Hawaiian: ) is the second-largest of the islands of the state of Hawaii at 727.2 square miles (1,883 km2) and is the 17th largest island in the United States. Maui is the largest of Maui County's four islands, which ...

, but the between the two islands and lack of apparent geological evidence have cast this testimony in doubt. Thus the first entirely confirmed historically witnessed eruption was a January 1843 event; since that time Mauna Loa has erupted 32 times. Historical eruptions at Mauna Loa are typically Hawaiian in character and rarely violent, starting with the emergence of

lava fountain Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...

s over a several kilometer long

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

colloquially known as the "curtain of fire" (often, but not always, propagating from Mauna Loa's summit) and eventually concentrating at a single vent, its long-term eruptive center. Activity centered on its summit is usually followed by flank eruptions up to a few months later, and although Mauna Loa is historically less active than that of its neighbor Kilauea, it tends to produce greater volumes of lava over shorter periods of time. Most eruptions are centered at either the summit or either of its two major

s; within the last two hundred years, 38 percent of eruptions occurred at the summit, 31 percent at the northeast rift zone, 25 percent at the southwest rift zone, and the remaining 6 percent from northwest vents. 40 percent of the volcano's surface consists of lavas less than a thousand years old, and 98 percent of lavas less than 10,000 years old. In addition to the summit and rift zones, Mauna Loa's northwestern flank has also been the source of three historical eruptions. The 1843 event was followed by eruptions in 1849, 1851, 1852, and 1855, with the 1855 flows being particularly extensive. 1859 marked the largest of the three historical flows that have been centered on Mauna Loa's northwestern flank, producing a long lava flow that reached the ocean on Hawaii island's west coast, north of Kīholo Bay. An eruption in 1868 occurred alongside the enormous 1868 Hawaii earthquake, a

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

eight event that claimed 77 lives and remains the largest earthquake ever to hit the island. Following further activity in 1871, Mauna Loa experienced nearly continuous activity from August 1872 through 1877, a long-lasting and voluminous eruption lasting approximately 1,200 days and never moving beyond its summit. A short single-day eruption in 1877 was unusual in that it took place underwater, in

Kealakekua Bay Kealakekua Bay is located on the Kona coast of the island of Hawaii about south of Kailua-Kona. Settled over a thousand years ago, the surrounding area contains many archeological and historical sites such as religious temples (heiaus) and also ...

, and within a mile of the shoreline; curious onlookers approaching the area in boats reported unusually turbulent water and occasional floating blocks of hardened lava. Further eruptions occurred in 1879 and then twice in 1880, the latter of which extended into 1881 and came within the present boundaries of the island's largest city,

; however, at the time, the settlement was a shore-side village located further down the volcano's slope, and so was unaffected. File:Hawaii Volcanoes Hazard Map.svg, 275px, Clickable imagemap of the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

hazard mapping for Hawaii island; the lowest numbers correspond with the highest hazard levels. poly 25 186 49 180 73 150 54 108 36 100 24 104 5 123 3 137 22 164 Hualalai poly 54 64 99 63 113 40 78 23 74 12 46 5 37 21 41 44 Kohala poly 247 157 236 157 203 198 172 202 149 230 128 277 173 250 193 248 249 226 287 186 259 173 Kilauea poly 56 65 99 64 116 38 188 66 224 103 221 134 194 140 139 143 93 123 60 92 53 79

desc bottom-left Mauna Loa continued its activity, and of the eruptions that occurred in 1887, 1892, 1896, 1899, 1903 (twice), 1907, 1914, 1916, 1919, and 1926, three (in 1887, 1919, and 1926) were partially subaerial. The 1926 eruption in particular is noteworthy for having inundated a village near Hoōpūloa, destroying 12 houses, a church, and a small harbor. After an event in 1933, Mauna Loa's 1935 eruption caused a public crisis when its flows started to head towards Hilo. A bombing operation was decided upon to try and divert the flows, planned out by then-

lieutenant colonel Lieutenant colonel ( , ) is a rank of commissioned officers in the armies, most marine forces and some air forces of the world, above a major and below a colonel. Several police forces in the United States use the rank of lieutenant colone ...

George S. Patton George Smith Patton Jr. (November 11, 1885 – December 21, 1945) was a general in the United States Army who commanded the Seventh United States Army in the Mediterranean Theater of World War II, and the Third United States Army in France ...

. The bombing, conducted on December 27, was declared a success by Thomas A. Jaggar, director of the

, and lava stopped flowing by January 2, 1936. However, the role the bombing played in ending the eruption has since been heavily disputed by volcanologists. A longer but summit-bound event in 1940 was comparatively less interesting. Mauna Loa's 1942 eruption occurred only four months after the

attack on Pearl Harbor The attack on Pearl HarborAlso known as the Battle of Pearl Harbor was a surprise military strike by the Imperial Japanese Navy Air Service upon the United States against the naval base at Pearl Harbor in Honolulu, Territory of Hawaii, j ...

and the United States' entry into

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, and created a unique problem for the wartime United States. Occurring during an enforced nighttime blackout on the island, the eruption's luminosity forced the government to issue a

gag order A gag order (also known as a gagging order or suppression order) is an order, typically a legal order by a court or government, restricting information or comment from being made public or passed onto any unauthorized third party. The phrase may ...

on the local press, hoping to prevent news of its occurrence spreading, for fear that the Japanese would use it to launch a bombing run on the island. However, as flows from the eruption rapidly spread down the volcano's flank and threatened the ʻOlaʻa

flume A flume is a human-made channel for water, in the form of an open declined gravity chute whose walls are raised above the surrounding terrain, in contrast to a trench or ditch. Flumes are not to be confused with aqueducts, which are built to tr ...

, Mountain View's primary

water source Water supply is the provision of water by public utilities, commercial organisations, community endeavors or by individuals, usually via a system of pumps and pipes. Public water supply systems are crucial to properly functioning societies. Thes ...

, the

United States Army Air Force The United States Army Air Forces (USAAF or AAF) was the major land-based aerial warfare service component of the United States Army and ''de facto'' aerial warfare service branch of the United States during and immediately after World War II ...

decided to drop its own bombs on the island in the hopes of redirecting the flows away from the flume; sixteen bombs weighing between each were dropped on the island, but produced little effect. Eventually, the eruption ceased on its own. Following a 1949 event, the next major eruption at Mauna Loa occurred in 1950. Originating from the volcano's southwestern rift zone, the eruption remains the largest rift event in the volcano's modern history, lasting 23 days, emitting 376 million cubic meters of lava, and reaching the distant ocean within 3 hours. The 1950 eruption was not the most voluminous eruption on the volcano (the long-lived 1872–1877 event produced more than twice as much material), but it was easily one of the fastest-acting, producing the same amount of lava as the 1859 eruption in a tenth of the time. Flows overtook the village of Hoʻokena-mauka in

South Kona Kona is a ''moku'' or district on the Big Island of Hawaii in the State of Hawaii, known for its Kona coffee and the location of the Ironman World Championship Triathlon. In the current system of administration of Hawaii County, the ''moku'' ...

, crossed Hawaii Route 11, and reached the sea within four hours of eruption. Although there was no loss of life, the village was permanently destroyed. After the 1950 event, Mauna Loa entered an extended period of dormancy, interrupted only by a small single-day summit event in 1975. However, it rumbled to life again in 1984, manifesting first at Mauna Loa's summit, and then producing a narrow, channelized

ʻaʻā Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...

flow that advanced downslope within of Hilo, close enough to illuminate the city at nighttime. However, the flow got no closer, as two natural levees further up its pathway consequently broke and diverted active flows. From 1985 to 2022, the volcano had its longest period of quiet in recorded history. Magma had been accumulating beneath Mauna Loa since the 1984 eruption, and the U.S. Geological Survey in February 2021 reported that although an eruption "did not appear to be imminent," the volcano had shown elevated signs of unrest since 2019, including a slight increase in the rate of inflation at the volcano's summit. The quiet period ended at 11:30 PM HST on November 27, 2022, when an eruption began at the volcano's summit in Moku‘āweoweo (Mauna Loa's caldera). Lava flows emanating from the caldera became visible from

Kailua-Kona Kailua-Kona is an unincorporated community and census-designated place (CDP) in Hawaii County, Hawaii, United States. It is also known as Kailua (a name it shares with a community located on the windward side of Oahu), as Kona (a name it shares ...

in the hours immediately following the eruption. The eruption remained confined to the caldera until approximately 6:30 AM HST on November 28, when the Hawaiian Volcano Observatory observed that the eruption had migrated from the summit to the Northeast Rift Zone. Three fissures were initially observed in the rift zone, with the first two becoming inactive by 1:30 PM on the 28th. Before becoming inactive, the two upper fissures fed lava flows that moved downslope, however those flows stalled approximately from

Saddle Road Route 200, known locally as Saddle Road, traverses the width of the Island of Hawaii, from downtown Hilo to its junction with Hawaii Route 190 near Waimea. The road was once considered one of the most dangerous paved roads in the state, with ...

. Lava fountains were also observed emanating from the fissures, with the tallest reaching up to into the air. As lava flows from the third fissure expanded, they cut off the road to the

at approximately 8 PM on the 28th. Activity in the rift zone continued on the 29th, with a fourth fissure that opened at approximately 7:30 PM on the 28th joining the third in releasing lava flows. The main front of the third fissure's lava flows also continued to move, and was located approximately from Saddle Road at 7 AM on December 2nd. As the eruption approached its second week, indications of a reduction in activity began to appear. On December 8th, the lava flows feeding the main front began to drain, and the main flow front stalled approximately from Saddle Road. The flows continued to drain on the 9th, and the third fissure's lava fountains also began to grow shorter. On the 10th, the lava fountains were replaced by a lava pond, and the stalled flow front was declared to no longer be a threat. Based on these factors and data on past eruptions, the HVO determined that the eruption may end soon and reduced the volcano alert level from Warning to Watch at 2:35 PM on the 10th. However, there was a small possibility that the eruption would continue at a very low rate. The eruption officially ended at 7:17 AM on the 13th, and the HVO lowered the volcano alert level to Advisory.

Hazards

Mauna Loa has been designated a

Decade Volcano The Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and prox ...

, one of the sixteen volcanoes identified by the

International Association of Volcanology and Chemistry of the Earth's Interior The International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) is a learned society that focuses on research in volcanology, efforts to mitigate volcanic disasters, and research into closely related disciplines, such ...

(IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas. The

maintains a hazard zone mapping of the island done on a one to nine scale, with the most dangerous areas corresponding the smallest numbers. Based on this classification Mauna Loa's continuously active summit caldera and rift zones have been given a level one designation. Much of the area immediately surrounding the rift zones is considered level two, and about 20 percent of the area has been covered in lava in historical times. Much of the remainder of the volcano is hazard level three, about 15 to 20 percent of which has been covered by flows within the last 750 years. However, two sections of the volcano, the first in the Naalehu area and the second on the southeastern flank of Mauna Loa's rift zone, are protected from eruptive activity by local topography, and have thus been designated hazard level 6, comparable with a similarly isolated segment on

. Although volcanic eruptions in Hawaiʻi rarely produce casualties (the only direct historical fatality due to volcanic activity on the island occurred at Kīlauea in 1924, when an unusually explosive eruption hurled rocks at an onlooker), property damage due to inundation by lava is a common and costly hazard. Hawaiian-type eruptions usually produce extremely slow-moving flows that advance at walking pace, presenting little danger to human life, but this is not strictly the case; Mauna Loa's 1950 eruption emitted as much lava in three weeks as Kīlauea's recent eruption produced in three years and reached sea level within four hours of its start, overrunning the village of Hoʻokena Mauka and a major highway on the way there. An earlier eruption in 1926 overran the village of Hoʻōpūloa Makai, and

, partly built on lavas from the 1880–81 eruption, is at risk from future eruptions. The 1984 eruption nearly reached the city, but stopped short after the flow was redirected by upstream topography. A potentially greater hazard at Mauna Loa is a sudden, massive collapse of the volcano's flanks, like the one that struck the volcano's west flank between 100,000 and 200,000 years ago and formed the present-day

. Deep

fault lines In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

are a common feature on Hawaiian volcanoes, allowing large portions of their flanks to gradually slide downwards and forming structures like the

and the ancient Ninole Hills; large earthquakes could trigger rapid flank collapses along these lines, creating massive

landslide Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated grade (slope), slope failures, mudflows, and debris flows. Landslides occur in a variety of ...

s and possibly triggering equally large

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

s. Undersea surveys have revealed numerous landslides along the Hawaiian chain and evidence of two such giant tsunami events: 200,000 years ago,

Molokaʻi Molokai , or Molokai (), is the fifth most populated of the eight major islands that make up the Hawaiian Islands archipelago in the middle of the Pacific Ocean. It is 38 by 10 miles (61 by 16 km) at its greatest length and width with a us ...

experienced a tsunami, and 100,000 years ago a

megatsunami A megatsunami is a very large wave created by a large, sudden displacement of material into a body of water. Megatsunamis have quite different features from ordinary tsunamis. Ordinary tsunamis are caused by underwater tectonic activity (movemen ...

high struck Lānaʻi. A more recent example of the risks associated with slumps occurred in

1975 It was also declared the ''International Women's Year'' by the United Nations and the European Architectural Heritage Year by the Council of Europe. Events January * January 1 - Watergate scandal (United States): John N. Mitchell, H. R. ...

, when the Hilina Slump suddenly lurched forward several meters, triggering a 7.2 earthquake and a tsunami that killed two campers at Halape.

Monitoring

Established on Kīlauea in 1912, the

(HVO), presently a branch of the United States Geological Survey, is the primary organization associated with the monitoring, observance, and study of Hawaiian volcanoes. Thomas A. Jaggar, the Observatory's founder, attempted a summit expedition to Mauna Loa to observe its 1914 eruption, but was rebuffed by the arduous trek required (see Ascents). After soliciting help from

Lorrin A. Thurston Lorrin Andrews Thurston (July 31, 1858 – May 11, 1931) was an American lawyer, politician, and businessman born and raised in the Kingdom of Hawaii. Thurston played a prominent role in the Overthrow of the Hawaiian Kingdom that replaced Q ...

, in 1915 he was able to persuade the

US Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...

to construct a "simple route to the summit" for public and scientific use, a project completed in December of that year; the Observatory has maintained a presence on the volcano ever since. Eruptions on Mauna Loa are almost always preceded and accompanied by prolonged episodes of seismic activity, the monitoring of which was the primary and often only warning mechanism in the past and which remains viable today. Seismic stations have been maintained on Hawaiʻi since the Observatory's inception, but these were concentrated primarily on Kīlauea, with coverage on Mauna Loa improving only slowly through the 20th century. Following the invention of modern monitoring equipment, the backbone of the present-day monitoring system was installed on the volcano in the 1970s. Mauna Loa's July 1975 eruption was forewarned by more than a year of seismic unrest, with the HVO issuing warnings to the general public from late 1974; the 1984 eruption was similarly preceded by as much as three years of unusually high seismic activity, with

volcanologist A volcanologist, or volcano scientist, is a geologist who focuses on understanding the formation and eruptive activity of volcanoes. Volcanologists frequently visit volcanoes, sometimes active ones, to observe and monitor volcanic eruptions, col ...

s predicting an eruption within two years in 1983. The modern monitoring system on Mauna Loa consists not only of its local seismic network but also of a large number of

GPS The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...

stations,

tiltmeter A tiltmeter is a sensitive inclinometer designed to measure very small changes from the vertical level, either on the ground or in structures. Tiltmeters are used extensively for monitoring volcanoes, the response of dams to filling, the small ...

s, and strainmeters that have been anchored on the volcano to monitor

due to swelling of Mauna Loa's subterranean

, which presents a more complete picture of the events proceeding eruptive activity. The GPS network is the most durable and wide-ranging of the three systems, while the tiltmeters provide the most sensitive predictive data, but are prone to erroneous results unrelated to actual ground deformation; nonetheless a survey line across the caldera measured a increase in its width over the year preceding the 1975 eruption, and a similar increase in 1984 eruption. Strainmeters, by contrast, are relatively rare. The Observatory also maintains two

gas detector A gas detector is a device that detects the presence of gases in an area, often as part of a safety system. A gas detector can sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave. This type of d ...

s at Mokuʻāweoweo, Mauna Loa's summit caldera, as well as a publicly accessibl
live webcam
and occasional screenings by

imaging.

Human history

Pre-contact

The first

Ancient Hawaiian Ancient Hawaii is the period of Hawaiian history preceding the unification in 1810 of the Kingdom of Hawaii by Kamehameha the Great. Traditionally, researchers estimated the first settlement of the Hawaiian islands as having occurred sporadic ...

s to arrive on Hawaii island lived along the shores where food and water were plentiful. Flightless birds that had previously known no predators became a staple food source. Early settlements had a major impact on the local ecosystem, and caused many extinctions, particularly amongst bird species, as well as introducing foreign plants and animals and increasing erosion rates. The prevailing lowland forest ecosystem was transformed from forest to grassland; some of this change was caused by the use of fire, but the main reason appears to have been the introduction of the

Polynesian rat The Polynesian rat, Pacific rat or little rat (''Rattus exulans''), known to the Māori as ''kiore'', is the third most widespread species of rat in the world behind the brown rat and black rat. The Polynesian rat originated in Southeast Asia, a ...

(''Rattus exulans''). Ancient Hawaiian

religious practice Religion is usually defined as a social-cultural system of designated behaviors and practices, morals, beliefs, worldviews, texts, sanctified places, prophecies, ethics, or organizations, that generally relates humanity to supernatural, tran ...

holds that the five volcanic peaks of the island are sacred, and regards Mauna Loa, the largest of them all, with great admiration; but what mythology survives today consists mainly of oral accounts from the 18th century first compiled in the 19th. Most of these stories agree that the Hawaiian

volcano goddess A volcano deity is a deification of a volcano. Volcano gods include: * Vulcan, in ancient Roman religion and myth, the god of fire including the fire of volcanoes, deserts, metalworking, and the forge. *Volos, Slavic god of earth, waters, and the ...

, Pele, resides in

Halemaʻumaʻu Halemaumau (''six syllables: HAH-lay-MAH-oo-MAH-oo'') is a pit crater within the much larger Kīlauea Caldera at the summit of Kīlauea volcano on island of Hawaiʻi. The roughly circular crater was x before collapses that roughly doubled ...

on Kilauea; however a few place her home at Mauna Loa's summit caldera Mokuʻāweoweo, and the mythos in general associates her with all volcanic activity on the island. Regardless, Kīlauea's lack of a geographic outline and strong volcanic link to Mauna Loa led to it being considered an offshoot of Mauna Loa by the Ancient Hawaiians, meaning much of the mythos now associated with Kīlauea was originally directed at Mauna Loa proper as well. Ancient Hawaiians constructed an extensive trail system on Hawaiʻi island, today known as the

Ala Kahakai National Historic Trail Ala Kahakai National Historic Trail is a long trail located on the island of Hawaii. It is not yet a single continuous trail, but can be accessed at several broken segments along the coastline of the Big Island. The trail was established to acc ...

. The network consisted of short trailheads servicing local areas along the main roads and more extensive networks within and around agricultural centers. The positioning of the trails was practical, connecting living areas to farms and ports, and regions to resources, with a few upland sections reserved for gathering and most lines marked well enough to remain identifiable long after regular use had ended. One of these trails, the Ainapo Trail, ascended from the village of Kapāpala over in about and ended at Mokuʻāweoweo at Mauna Loa's summit. Although the journey was arduous and required several days and many porters, ancient Hawaiians likely made the journey during eruptions to leave offerings and prayers to honor Pele, much as they did at Halemaʻumaʻu, neighboring Kilauea's more active and more easily accessible caldera. Several camps established along the way supplied water and food for travelers.

European summiting attempts

James Cook James Cook (7 November 1728 Old Style date: 27 October – 14 February 1779) was a British explorer, navigator, cartographer, and captain in the British Royal Navy, famous for his three voyages between 1768 and 1779 in the Pacific Ocean an ...

's third voyage was the first to make landfall on Hawaiʻi island, in 1778, and following adventures along the North American west coast, Cook returned to the island in 1779. On his second visit

John Ledyard John Ledyard (November 1751 – 10 January 1789) was an American explorer and adventurer. Early life Ledyard was born in Groton, Connecticut, in November 1751. He was the first child of Abigail Youngs Ledyard and Capt. John Ledyard Jr, son o ...

, a

corporal Corporal is a military rank in use in some form by many militaries and by some police forces or other uniformed organizations. The word is derived from the medieval Italian phrase ("head of a body"). The rank is usually the lowest ranking non ...

of the

Royal Marines The Corps of Royal Marines (RM), also known as the Royal Marines Commandos, are the UK's special operations capable commando force, amphibious light infantry and also one of the five fighting arms of the Royal Navy. The Corps of Royal Marine ...

aboard , proposed and received approval for an expedition to the summit Mauna Loa to learn "about that part of the island, particularly the peak, the tip of which is generally covered with snow, and had excited great curiosity." Using a compass, Ledyard and small group of ships' mates and native attendants attempted to make a direct course for the summit. However, on the second day of traveling the route became steeper, rougher, and blocked by "impenetrable thickets," and the group was forced to abandon their attempt and return to

, reckoning they had "penetrated 24 miles and we suppose erewithin 11 miles of the peak"; in reality, Mokuʻāweoweo lies only east of the bay, a severe overestimation on Ledyard's part. Another of Cook's men,

Lieutenant A lieutenant ( , ; abbreviated Lt., Lt, LT, Lieut and similar) is a commissioned officer rank in the armed forces of many nations. The meaning of lieutenant differs in different militaries (see comparative military ranks), but it is often sub ...

James King, estimated the peak to be at least high based on its

snow line The climatic snow line is the boundary between a snow-covered and snow-free surface. The actual snow line may adjust seasonally, and be either significantly higher in elevation, or lower. The permanent snow line is the level above which snow wil ...

The next attempt to summit Mauna Loa was an expedition led by

Archibald Menzies Archibald Menzies ( ; 15 March 1754 – 15 February 1842) was a Scottish surgeon, botanist and naturalist. He spent many years at sea, serving with the Royal Navy, private merchants, and the Vancouver Expedition. He was the first recorded Euro ...

, a botanist and naturalist on the 1793

Vancouver Expedition The Vancouver Expedition (1791–1795) was a four-and-a-half-year voyage of exploration and diplomacy, commanded by Captain George Vancouver of the Royal Navy. The British expedition circumnavigated the globe and made contact with five continen ...

. In February of that year Menzies, two ships' mates, and a small group of native Hawaiian attendants attempted a direct course for the summit from

, making it inland by their reckoning (an overestimation) before they were turned away by the thickness of the forest. On a second visit by the expedition to the island in January of the next year Menzies was placed in charge of exploring the island interior, and after traversing the flanks of

he and his party arrived at the high plateau separating the two volcanoes. Menzies decided to make a second attempt (above the objections of the accompanying island chief), but again his progress was arrested by unassailable thickets. Menzies made a third attempt to summit Mauna Loa in February 1794. This time the botanist consulted King

Kamehameha I Kamehameha I (; Kalani Paiea Wohi o Kaleikini Kealiikui Kamehameha o Iolani i Kaiwikapu kaui Ka Liholiho Kūnuiākea; – May 8 or 14, 1819), also known as Kamehameha the Great, was the conqueror and first ruler of the Kingdom of Hawaii. T ...

for advice and learned that he could take canoes to the south and follow the ʻAinapō Trail, not knowing of its existence beforehand. Significantly better prepared, Menzies, Lieutenant Joseph Baker and Midshipman George McKenzie of ''Discovery'', and a servant (most likely Jonathan Ewins, listed on the ship's muster as "Botanist's L't") reached the summit, which Menzies estimated to be high with the aid of a

barometer A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis ...

(consistent with a modern value of ). He was surprised to find heavy snow and morning temperatures of , and was unable to compare the heights of Mauna Loa and Kea but correctly supposed the latter to be taller based on its larger snow cap. The feat of summitting Mauna Loa was not to be repeated for forty years. The Hawaiian Islands were the site of fervent missionary work, with the first group of missionaries arrived at

Honolulu Honolulu (; ) is the capital and largest city of the U.S. state of Hawaii, which is in the Pacific Ocean. It is an unincorporated county seat of the consolidated City and County of Honolulu, situated along the southeast coast of the island ...

in 1820 and the second in 1823. Some of these missionaries left for Hawaiʻi island, and spent ten weeks traveling around it, preaching at local villages and climbing Kilauea, from which one of its members, William Ellis, observed Mauna Loa with the aid of a telescope and ascertained it and Kea to be "perhaps 15,000 to 16,000 feet above the level of the sea"; they did not, however, attempt to climb the volcano itself. It is sometimes reported that the missionary Joseph Goodrich reached the summit around this time, but he never claimed this himself, though he did summit Mauna Kea and describe Mokuʻāweoweo with the aid of another telescope. The next successful ascent was made on January 29, 1834, by the Scottish botanist David Douglas, who also reached the summit caldera using the ʻAinapō Trail. By the time Douglas reached the summit the environment had put him under extreme duress, but he nonetheless stayed overnight to make measurements of the summit caldera's proportions and record barometric data on its height, both now known to be wildly inaccurate. Douglas collected biological samples on the way both up and down, and after a difficult and distressing descent began collating his samples; he planned to return to England, but instead several months later his body was discovered mysteriously crushed in a pit beside a dead wild boar Isidor Löwenstern successfully climbed Mauna Loa in February 1839, only the third successful climb in 60 years.

Wilkes expedition

The

United States Exploring Expedition The United States Exploring Expedition of 1838–1842 was an exploring and surveying expedition of the Pacific Ocean and surrounding lands conducted by the United States. The original appointed commanding officer was Commodore Thomas ap Catesby ...

led by Lieutenant

Charles Wilkes Charles Wilkes (April 3, 1798 – February 8, 1877) was an American naval officer, ship's captain, and explorer. He led the United States Exploring Expedition (1838–1842). During the American Civil War (1861–1865), he commanded ' during the ...

was tasked with a vast survey of the Pacific Ocean starting in 1838. In September 1840 they arrived in

, where repairs to the ships took longer than expected. Wilkes decided to spend the winter in Hawaii and take the opportunity to explore its volcanoes while waiting for better weather to continue the expedition. King

Kamehameha III Kamehameha III (born Kauikeaouli) (March 17, 1814 – December 15, 1854) was the third king of the Kingdom of Hawaii from 1825 to 1854. His full Hawaiian name is Keaweaweula Kīwalaō Kauikeaouli Kaleiopapa and then lengthened to Keaweaweula K� ...

assigned American medical missionary Dr.

Gerrit P. Judd Gerrit Parmele Judd (April 23, 1803 – July 12, 1873) was an American physician and missionary to the Kingdom of Hawaii who later renounced his American citizenship and became a trusted advisor and cabinet minister to King Kamehameha III. He ...

to the expedition as a translator. Wilkes sailed to

on the island of Hawaiʻi and decided to climb Mauna Loa first, since it looked easier than

. On December 14 he hired about 200 porters, but after he left he realized only about half the equipment had been taken, so he had to hire more Hawaiians at higher pay. When they reached Kīlauea after two days, their guide Puhano headed off to the established ʻAinapō Trail. Wilkes did not want to head back downhill so he blazed his own way through dense forest directed by a compass. The Hawaiians were offended by the waste of sacred trees which did not help morale. At about elevation they established a camp called "Sunday Station" at the edge of the forest. Two guides joined them at Sunday Station: Keaweehu, "the bird-catcher" and another whose Hawaiian name is not recorded, called "ragsdale". Although Wilkes thought he was almost to the summit, the guides knew they were less than halfway up. Since there was no water at Sunday Station, porters had to be sent back ten miles (16 km) to a

lava tube A lava tube, or pyroduct, is a natural conduit formed by flowing lava from a volcanic vent that moves beneath the hardened surface of a lava flow. If lava in the tube empties, it will leave a cave. Formation A lava tube is a type of lava ca ...

on ʻAinapō Trail which had a known supply. After an entire day replenishing stocks, they continued up to a second camp they called "Recruiting Station" at about elevation. After another full day's hike they established "Flag Station" on December 22, and by this time were on the ʻAinapō Trail. Most of the porters were sent back down to get another load. At the Flag Station Wilkes and his eight remaining men built a circular wall of lava rocks and covered the shelter with a canvas tent. A snowstorm was in progress and several suffered from

altitude sickness Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People can respond to high altitude in different ways. Sympt ...

. That night (December 23), the snow on the canvas roof caused it to collapse. At daylight some of the group went down the trail to retrieve firewood and the gear abandoned on the trail the day before. After another day's climb, nine men reached the rim of Mokuʻāweoweo. They could not find a way down its steep sides so chose a smooth place on the rim for the camp site, at coordinates . Their tent was pitched within of the crater's edge, secured by lava blocks. The next morning they were unable to start a fire using friction due to the thin air at that altitude, and sent for matches. By this time, the naval officers and Hawaiians could not agree on terms to continue hiring porters, so sailors and marines were ordered from the ships. Dr. Judd traveled between the summit and the Recruiting Station to tend the many who suffered from altitude sickness or had worn out their shoes on the rough rock. Christmas Day was spent building rock walls around the camp to give some protection from the high winds and blowing snow. It took another week to bring all the equipment to the summit, including a

pendulum A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the ...

designed for measuring slight variations in gravity. Moku-A-Weo-Weo

On December 31, 1840, the pre-fabricated pendulum house was assembled. Axes and chisels cut away the rock surface for the pendulum's base. It took another three days to adjust the clock to the point where the experiments could begin. However, the high winds made so much noise that the ticks could often not be heard, and varied the temperature to make measurements inaccurate. Grass had to be painstakingly brought from the lowest elevations for insulation to get accurate measurements. On Monday, January 11, Wilkes hiked around the summit crater. Using an optical method, he estimated Mauna Kea was higher, while modern measurements indicate a difference of about . On January 13, 1841, he had "Pendulum Peak, January 1841 U.S. Ex, Ex." cut into a rock at the site. The tents were dismantled and Hawaiians carried the gear down over the next three days, while Wilkes enjoyed a

lomilomi massage Lomilomi massage is a Polynesian method of kneading massage, but with overtones of the indigenous religious beliefs. The word ''lomilomi'' comes from the Hawaiian and Samoan languages. Lomi means "to knead.” The smooth flow of the strokes mim ...

. He continued his measurements at lower elevations and left the island on March 5. For all the effort he did not obtain any significant results, attributing gravity discrepancies to "the tides". The Wilkes expedition's camp site's ruins are the only known physical evidence in the Pacific of the U.S. Exploring Expedition. The camp site was listed on the

National Register of Historic Places The National Register of Historic Places (NRHP) is the United States federal government's official list of districts, sites, buildings, structures and objects deemed worthy of preservation for their historical significance or "great artistic v ...

on July 24, 1974, as site 74000295, and is state historic site 10-52-5507.

Today

A summit shelter was built with some of the stones from Wilkes' camp site and mortar in 1934. In 1916 Mokuʻāweoweo was included in

, and a new trail was built directly from park headquarters at Kīlauea, an even more direct route than the one taken by Wilkes. This trail, arriving at the summit from the east via Red Hill, became the preferred route due to its easier access and gentler slope. The historic ʻAinapō Trail fell into disuse, and was reopened in the 1990s. A third modern route to the summit is from the

up to the

which is at elevation a few miles north of Mokuʻāweoweo and the North Pit trail.

Climate

Trade wind The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisph ...

s blow from east to west across the Hawaiian islands, and the presence of Mauna Loa strongly affects the local climate. At low elevations, the eastern (windward) side of the volcano receives heavy rain;

is the wettest city in Hawaii and the fourth-wettest city in the United States, behind the

southeast Alaska Southeast Alaska, colloquially referred to as the Alaska(n) Panhandle, is the southeastern portion of the U.S. state of Alaska, bordered to the east and north by the northern half of the Canadian province of British Columbia (and a small part ...

n cities of Whittier,

Ketchikan Ketchikan ( ; tli, Kichx̱áan) is a city in and the borough seat of the Ketchikan Gateway Borough of Alaska. It is the state's southeasternmost major settlement. Downtown Ketchikan is a National Historic District. With a population at the 20 ...

and Yakutat. The rainfall supports extensive

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

ation. The western (leeward) side has a much drier climate. At higher elevations, the amount of precipitation decreases, and skies are very often clear. Very low temperatures mean that precipitation often occurs in the form of snow, and the summit of Mauna Loa is described as a ''

periglacial Periglaciation (adjective: "periglacial", also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and ot ...

'' region, where freezing and thawing play a significant role in shaping the landscape. Mauna Loa has a

tropical climate Tropical climate is the first of the five major climate groups in the Köppen climate classification identified with the letter A. Tropical climates are defined by a monthly average temperature of 18 °C (64.4 °F) or higher in the cool ...

with warm temperatures at lower elevations and cool to cold temperatures higher up year-round. Below is the table for the slope observatory, which is at in the

alpine zone Alpine tundra is a type of natural region or biome that does not contain trees because it is at high elevation, with an associated harsh climate. As the latitude of a location approaches the poles, the threshold elevation for alpine tundra gets ...

. The highest recorded temperature was and the lowest was on September 26, 1990, and February 20, 1962, respectively.

Observatories

Mauna Loa CO2 monthly mean concentration

The location of Mauna Loa has made it an important location for atmospheric monitoring by the

Global Atmosphere Watch The Global Atmosphere Watch (GAW) is a worldwide system established by the World Meteorological Organizationa United Nations agencyto monitor trends in the Earth's atmosphere. It arose out of concerns for the state of the atmosphere in the 1960s. ...

and other scientific observations. The

(MLSO), located at on the northern slope of the mountain, has long been prominent in observations of the

. The

NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...

(MLO) is located close by. From its location well above local human-generated influences, the MLO monitors the global atmosphere, including the

greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

. Measurements are adjusted to account for local

outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which a ...

of CO₂ from the volcano. The Yuan-Tseh Lee Array for Microwave Background Anisotropy (AMiBA) sits at an elevation of . It was established in October 2006 by the

Academia Sinica Institute of Astronomy and Astrophysics The Academia Sinica Institute of Astronomy and Astrophysics (also known as the Institute of Astronomy and Astrophysics, abbreviated as ASIAA or IAA. ) is a research institute of the national academy of Taiwan, Academia Sinica. ASIAA is currently ...

(ASIAA) to examine

cosmic microwave background radiation In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...

Notes

References

External links

Mauna Loa - United States Geological Survey

Global Volcanism Program entry

Mauna Loa Observatory (MLO) – NOAA

Mauna Loa Solar Observatory (MLSO)
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