The Twin Buttes are two

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

cinder cone A cinder cone (or scoria cone) is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions o ...

s located in the Cascade Mountain Range in Shasta County, California. They are part of the Bidwell Spring chain and lie within a region that was active in the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

. Formed during the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

between 25,000 and 15,000 years ago, the volcanoes erupted

lava flows 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 un ...

that coursed toward the Burney Mountain

lava dome In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions on ...

. These lava flows cover an area of and are made of

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 ...

and

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

. The volcanoes also erupted cinder and

volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...

that reached eastward. As of 2012, the Twin Buttes were still monitored by 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, ...

for deformation, an indicator of pre-eruptive activity. However, they are considered to have "low to very low" threat potential for future eruptive activity.

Geography

The Twin Buttes are two

volcanoes that lie north of Lassen Peak in Shasta County, California. The Twin Buttes reach a summit elevation of about . Nearby towns include

Burney Burney may refer to: __NOTOC__ Places * Burney, California, United States, an unincorporated town and census-designated place * Burney, Indiana, United States, an unincorporated community * Burney Falls, a waterfall in California * Burney (hill), ...

Old Station Old or OLD may refer to: Places * Old, Baranya, Hungary * Old, Northamptonshire, England *Old Street station, a railway and tube station in London (station code OLD) *OLD, IATA code for Old Town Municipal Airport and Seaplane Base, Old Town, ...

, and

Viola The viola ( , also , ) is a string instrument that is bow (music), bowed, plucked, or played with varying techniques. Slightly larger than a violin, it has a lower and deeper sound. Since the 18th century, it has been the middle or alto voice of ...

. About 6,700 people live within of the volcanoes, though the population within climbs to more than 260,000. The buttes are aligned north–northwest and lie at the center of the Bidwell Spring volcanic chain.

Geology

The Twin Buttes — and other volcanoes near Lassen Peak — are part of the Cascade Volcanic Arc, which was produced by

subduction 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 ...

of the oceanic Juan de Fuca tectonic plate under the North American tectonic plate. Volcanic activity in the region is also influenced by the westward

expansion Expansion may refer to: Arts, entertainment and media * ''L'Expansion'', a French monthly business magazine * ''Expansion'' (album), by American jazz pianist Dave Burrell, released in 2004 * ''Expansions'' (McCoy Tyner album), 1970 * ''Expansio ...

of the

Basin and Range Province The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating ...

into the Cascades. Volcanism in the region encompasses a wide variety of eruption types, ranging from cinder cones to

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 ...

es. Eruptive activity has for the most part produced overlapping,

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

volcanoes through nonexplosive to weak

explosive eruption In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such ...

s. Volcanic activity during the

has produced

basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Ameri ...

, and

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

tholeiite 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 ...

. Other major volcanic centers near the Twin Buttes include the Yana, Maidu, Dittmar, and Latour centers, which were long-lived volcanic systems with

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 ...

ranging in composition from

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomi ...

silicic Silicic is an adjective to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually defined as at least 63 percent. Granite and rhyolite are the most common silicic rocks. Silicic is the group ...

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

; these four systems are now eroded with extinct hydrothermal systems. The Bidwell Spring chain consists of five eruptive units including the Twin Buttes basalt. ⁴⁰Ar/³⁹Ar has placed two other deposits, basaltic andesite from Black Butte and andesite from Bidwell Spring, at 62,000 ± 10,000 years old and 68,000 ± 6,000 years old, respectively. These results suggest several small eruptions between 65,000 and 45,000 years ago from the Bidwell Spring chain. Two other basaltic andesite deposits from the chain have been described by the

(USGS), which considers the Bidwell Spring chain as part of the Caribou Volcanic Field, a system of 11 eruptive sequences between 200,000 and 100,000 years ago with vents aligned with faults that focused surface volcanic activity. Basalt from the Twin Buttes overlies eruptive material from the Poison Lake Chain and the Cone Lake Chain, which are also within the Caribou Volcanic field. Twin Buttes basalt is overlain by basaltic andesite erupted during the late

from an unnamed volcanic vent, which is thought to be between 45,000 and 25,000 years old.

Subfeatures

Subfeatures of the formation include Red Rock Hill, which has an elevation of . Other nearby features include basaltic andesite and a distinct basalt deposit southeast and northeast of the Twin Buttes, respectively, both of which were produced by eruptive activity between 50,000 and 35,000 years ago.

Eruptive history

Located in an area that was highly active during the Quaternary, the Twin Buttes volcanoes formed during the late Pleistocene. The North and South Twin Buttes erupted blocky, partially unvegetated

lava flow 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 that moved north toward the southeastern base of Burney Mountain, a

, between 25,000 and 15,000 years ago, covering an area of . They have an overall volume of . Eruptive material consisted of basalt (including

picrite basalt Picrite basalt or picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite. The olivine-rich p ...

) and

. Basalt erupted from Twin Buttes forms part of the Bidwell Spring chain with an ⁴⁰Ar/³⁹Ar age of about 46,000 ± 3,000 years, covering an area of . The basalt deposit has a total volume of . At the edges, lava flows are steep, with up to of

relief Relief is a sculptural method in which the sculpted pieces are bonded to a solid background of the same material. The term ''relief'' is from the Latin verb ''relevo'', to raise. To create a sculpture in relief is to give the impression that the ...

. The lava flows from the Twin Buttes are

porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all ...

with about 53%

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 ...

content; they have vesicular surfaces and dense interiors. Phenocrysts range from ; there are also coarse

xenolith A xenolith ("foreign rock") is a rock fragment (country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in igne ...

s of

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

throughout the lava flows. Cinder and

erupted by the Twin Buttes extend to the east. While Twin Buttes last erupted during the late Pleistocene, the area is still monitored by the USGS given its proximity to Lassen Peak. As of 2012, there were three

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 ...

receivers continuously monitoring Twin Buttes for deformation, an indicator of pre-eruptive activity. In 2014, the USGS considered Twin Buttes to have "low to very low" threat potential for a future eruption.

Notes

* The

Global Volcanism Program The Smithsonian Institution's Global Volcanism Program (GVP) documents Earth's volcanoes and their eruptive history over the past 10,000 years. The mission of the GVP is to document, understand, and disseminate information about global volcanic a ...

of the

Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...

lists the Twin Buttes summit elevation as . However, the

Geographic Names Information System The Geographic Names Information System (GNIS) is a database of name and locative information about more than two million physical and cultural features throughout the United States and its territories, Antarctica, and the associated states of ...

lists its elevation as . * The Global Volcanism Program lists Twin Buttes as a Pleistocene volcano. Archived materials published by the

lists it as late Pleistocene or early Holocene.

References

Sources

* * * *{{cite journal, last1=Muffler, first1=L.J.P., last2=Clynne, first2=M.A., last3=Calvert, first3=A.T., last4=Champion, first4=D.E., url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article/123/11-12/2177/125589/Diverse-discrete-mantle-derived-batches-of-basalt, title=Diverse, discrete, mantle-derived batches of basalt erupted along a short normal fault zone: The Poison Lake chain, southernmost Cascades, date=November 1, 2011, publisher=

Geological Society of America The Geological Society of America (GSA) is a nonprofit organization dedicated to the advancement of the geosciences. History The society was founded in Ithaca, New York, in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitchco ...

, journal=

Geological Society of America Bulletin The ''Geological Society of America Bulletin'' (until 1960 called ''The Bulletin of the Geological Society of America'' and also commonly referred to as ''GSA Bulletin'') is a peer-reviewed scientific journal that has been published by the Geolo ...

, volume=123, issue=11–12, pages=2177–2200, doi=10.1130/B30370.1, bibcode=2011GSAB..123.2177M Volcanoes of California Cascade Volcanoes Subduction volcanoes Cinder cones of the United States Cascade Range Volcanoes of Shasta County, California Pleistocene volcanoes