Pahvant Butte (also Pavant Butte) is a

butte __NOTOC__ In geomorphology, a butte () is an isolated hill with steep, often vertical sides and a small, relatively flat top; buttes are smaller landforms than mesas, plateaus, and tablelands. The word ''butte'' comes from a French word mea ...

formed by a dormant

volcano 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 are ...

in the west-central portion of

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

, United States.

Description

The butte, sometimes called "Sugarloaf Mountain" by locals, is located in the

Sevier Desert The Sevier Desert is a large arid section of central-west Utah, United States, and is located in the southeast of the Great Basin. It is bordered by deserts north, west, and south; its east border is along the mountain range and valley sequences ...

in the Pahvant Valley south of

Delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also re ...

and five miles east of Clear Lake and the Clear Lake Wildlife Management Area. The butte has two peaks. The north peak has an elevation of and the south peak reaches . The peaks are about 1000 feet above the surrounding valley floor. The butte is about in diameter at the base. It formed in an active area of volcanism on top of

pahoehoe 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 ...

and

aa lava 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. Originally a

subaqueous volcano A subaqueous volcano is a volcano formed beneath freshwater and which never builds above lake level. They are commonly in the form of gently sloping tuff cones, although they can sometimes have an , such as White Horse Bluff in the Wells Gray-Cl ...

, it erupted out of the floor of

Lake Bonneville Lake Bonneville was the largest Late Pleistocene paleolake in the Great Basin of western North America. It was a pluvial lake that formed in response to an increase in precipitation and a decrease in evaporation as a result of cooler temperature ...

approximately 15,500 years ago.

Unusual Structure

Pahvant Butte obelisk ring 1974 4WPG011071004

Along the southeast rim of the inner depression of the volcano is an unfinished structure consisting of a concrete building embedded in the hill surrounded by two rings of concrete obelisks. The structure was apparently begun by a man named A. H. Hood, with the intention of generating wind power, in 1923.

Geography and geology

Part of the

Black Rock Desert volcanic field The Black Rock Desert volcanic field in Millard County, Utah, is a cluster of several volcanic features of the Great Basin including Pahvant Butte, The Cinders, and Tabernacle Hill. The field's Ice Springs event was an explosive eruption follo ...

of 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 ...

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

age, Pahvant Butte formed above older

and

s of the Pahvant field. The volcano was originally a

formed under

by a large eruption about 15,500 years ago. The water depth at the time of eruption is estimated to have been . This eruptive activity probably ejected steam,

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 ...

, and other materials out of the lake, enveloping the surrounding area with ash and spawning large waves in the lake. The eruption released particles 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 ...

ic lava into the air, which fell back to form

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...

. A

raised beach A raised beach, coastal terrace,Pinter, N (2010): 'Coastal Terraces, Sealevel, and Active Tectonics' (educational exercise), from 2/04/2011/ref> or perched coastline is a relatively flat, horizontal or gently inclined surface of marine origin,P ...

, or lacustrine terrace, formed by waves surrounds most of the volcano's lower rock. A vertical cliff, known as the Lace Curtain, is present on the north flank of the volcano, formed as a result of storm wave action. This name originated from the distinct white,

lace Lace is a delicate fabric made of yarn or thread in an open weblike pattern, made by machine or by hand. Generally, lace is divided into two main categories, needlelace and bobbin lace, although there are other types of lace, such as knitted o ...

-like pattern seen on the cliff face, caused by partial cementation of the tuff by minerals deposited by groundwater. Pahvant Butte was overlapped by the lava flows of the Ice Springs eruption between 1140 and 1440 AD.

Morphology

The Pahvant Butte volcano consists of an asymmetrical tuff cone with a breach on its southwestern side — and a platform area that extends to the southeast of the cone, formed of beds of

tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they rem ...

dipping steeply away from the cone, and partly concealing a mound of near horizontally-bedded

sideromelane Sideromelane is a vitreous basaltic volcanic glass, usually occurring in palagonite tuff, for which it is characteristic. It is a less common form of tachylite, with which it usually occurs together; however it lacks the iron oxide crystals dis ...

tephra beneath.

History of development

The mound of sub-horizontally bedded tephra represents the first stage of the eruption. The ash grains are variably vesiculated, a texture typical of material erupted during

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, which involves direct interaction between magma and water. The layers of ash and

lapilli Lapilli is a size classification of tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. ''Lapilli'' (singular: ''lapillus'') is Latin for "little stones". By definition lapilli range f ...

, incorporating some clasts of deformed lake sediments, were deposited by

sediment gravity flow upright=1.25, This turbidite from the Devonian Becke-Oese Sandstone">Devonian.html" ;"title="turbidite from the Devonian">turbidite from the Devonian Becke-Oese Sandstone of Germany is an example of a deposit from a sediment gravity flow. Note th ...

s. Some large ejected blocks have bedding sags beneath them, indicating a

ballistic Ballistics may refer to: Science * Ballistics, the science that deals with the motion, behavior, and effects of projectiles ** Forensic ballistics, the science of analyzing firearm usage in crimes ** Internal ballistics, the study of the proce ...

emplacement. The uppermost part of the mound consists of moderately vesicular ash with lapilli, passing up into ripple-marked beds at the base of the overlying cone deposits. These beds are interpreted to represent the result of wave reworking. The cone consists of steeply dipping layers of mainly

palagonite Palagonite is an alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt. Palagonite can also result from the interaction between water and basalt melt. The water flashes to steam on contact w ...

, formed by the alteration of the original basaltic glass. The cone is typical of tuff cones, which form during eruptions in the presence of standing water or abundant groundwater. This part of the volcano was constructed sub-aerially. The platform consists of deposits formed by the erosion of the cone. These built out into the lake as a prograding

delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also re ...

or beach, forming large

cross bedding In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original ...

foresets A foreset bed is one of the main parts of a river delta. It is the inclined part of a delta that is found at the end of the stream channel as the delta sediment is deposited along the arcuate delta front. As the sediments are deposited on a sloping ...

References

External links

{{commons category-inline, Pahvant Butte Volcanoes of Utah Buttes of the United States Volcanic fields of the Great Basin section Landforms of Millard County, Utah Volcanic fields of Utah