Asphalt Volcano
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Asphalt volcanoes are a rare variety of
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 ...
(
seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...
). They were unknown before 2003. Several examples have been found along the coasts of the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
and
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
and elsewhere, some still showing activity. Asphalt volcanoes resemble other seamounts however they are made entirely of
asphalt Asphalt most often refers to: * Bitumen, also known as "liquid asphalt cement" or simply "asphalt", a viscous form of petroleum mainly used as a binder in asphalt concrete * Asphalt concrete, a mixture of bitumen with coarse and fine aggregates, u ...
. The structures are thought to form above geologic faults through which
petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...
seeps from deeper in the Earth's crust.


Formation and distribution

Asphalt volcanoes are vents on the ocean floor through which asphalt erupts rather than of lava. They were discovered in the
Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...
during an expedition of the research vessel SONNE, led by Gerhard Bohrmann of the DFG Research Center Ocean Margins. These volcanoes host a previously unknown and highly diverse ecosystem at a water depths of more than 3,000 meters.Asphalt volcanoes discovered
Press Release 13. University of Bremen center for marine environmental sciences. May, 2004. Retrieved 5 July 2010.
The first asphalt volcanoes were discovered in 2003 by a research expedition to the
Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...
. They are located on a seafloor hill named "Chapopote,"
Nahuatl Nahuatl ( ; ), Aztec, or Mexicano is a language or, by some definitions, a group of languages of the Uto-Aztecan language family. Varieties of Nahuatl are spoken by about Nahuas, most of whom live mainly in Central Mexico and have smaller popul ...
for "tar." The site is located in a field of
salt dome A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered us ...
s known as the Campeche Knolls, a series of steep hills formed from salt bodies that rise from underlying rock, a common feature in the gulf. The research team documented tar flows as wide as across. Also discovered alongside the asphalt were areas soaked with
petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...
and
methane hydrate Methane clathrate (CH4·5.75H2O) or (4CH4·23H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large am ...
, also spewed from the volcano. This kind of an environment proves attractive to chemical-loving bacteria and tubeworms, although the exact biogeochemical relationship is not yet known. One hypothesis is that the tar is relatively hot when it comes out of the seafloor, but just like undersea
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 Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
flows, it is quickly cooled by the much colder seawater around it. This produces forms similar to the distinctive
A'a 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 unde ...
and
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 unde ...
types 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 ...
lava flow seen in places like
Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
. Another similarity is that the tar heats methane hydrate and causes it to explode into a free gas, similar to the action hot lava has on
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...
in
phreatomagmatic eruption 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 ...
s. The team proposed an asphalt volcano formation theory in a paper published in ''
Eos In ancient Greek mythology and Ancient Greek religion, religion, Eos (; Ionic Greek, Ionic and Homeric Greek ''Ēṓs'', Attic Greek, Attic ''Héōs'', "dawn", or ; Aeolic Greek, Aeolic ''Aúōs'', Doric Greek, Doric ''Āṓs'') is the go ...
''. The article suggested that water heated past the critical point underneath the seafloor found a passageway to the surface, most likely a
salt dome A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered us ...
, and carried with it a heavy load of
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...
s and dissolved minerals. A special property of such critically heated water is that it can mix with oils, whereas normal water cannot. The same process is attributed to the formation of
black smoker Hydrothermal vents are fissures on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hots ...
s. Once the water reaches the surface, it cools, and its carrying capacity drops. The lighter compounds in the mixture escape to the surface, while the tar and other heavier materials remain on the seafloor, eventually building up the asphalt volcano's structure. The role of temperature in asphalt volcanism is debated, with evidence suggesting asphalt does not erupt in a hot state. Instead, the
pāhoehoe 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 unde ...
-like textures might result from gradients in viscosity, driven by the loss of volatile components, which create a contrast between the flow's outer crust and its inner core. In 2007, seven more such structures were discovered off the coast of
Santa Barbara, California Santa Barbara (, meaning ) is a coastal city in Santa Barbara County, California, of which it is also the county seat. Situated on a south-facing section of coastline, the longest such section on the West Coast of the United States excepting A ...
, by a team led by David Valentine. The largest of these domes lies at a depth of . The structures were larger than a football field and about as tall as a six-story building, all made completely out of asphalt. The unusual features were first noted by Ed Keller on bathymetric surveys conducted in the 1990s, and first viewed in 2007, utilizing AUV AUV Sentry and ''
DSV Alvin ''Alvin'' (DSV-2) is a crewed deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution (WHOI) of Woods Hole, Massachusetts. The original vehicle was built by General Mills' Electr ...
''. Samples were brought up for testing at
UC Santa Barbara The University of California, Santa Barbara (UC Santa Barbara or UCSB) is a public land-grant research university in Santa Barbara County, California, United States. Tracing its roots back to 1891 as an independent teachers college, UCSB joined ...
and the
Woods Hole Oceanographic Institution The Woods Hole Oceanographic Institution (WHOI, acronym pronounced ) is a private, nonprofit research and higher education facility dedicated to the study of marine science and engineering. Established in 1930 in Woods Hole, Massachusetts, it i ...
. Two further dives with DSV ''Alvin'' in 2009 and a detailed photographic survey of the area by the autonomous underwater vehicle ''Sentry'' showed many similarities to volcanic flows, including flow texture and cracking of the asphalt layers.
Carbon 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 ...
puts the structures at between 30 and 40 thousand years old. They had at one time been a prolific source of
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
. The two largest structures, less than apart, are pocked by pits and depressions, a sign of methane gas bubbling up long ago. Although the structures are still emitting residual gas, at present the amounts are too small to have any effect. The amount of crude oil in the largest of the structures alone is "enough to fuel my Honda Civic for about half a billion miles. oweverthe quality of the material is very poor...It's not worth something like light sweet crude," said Valentine. The petroleum in the structure is more viscous than that which is usually found in underground wells. This is because it has had less time to "bake" under the Earth's heat before being released. In addition, as much as 20% of its mass is made of "junk"—microscopic organisms, sand, and miscellaneous materials that gradually accumulated in the oil. Analysis of the samples collected from the mounds suggest that they required several decades, even centuries, to build up their current bulk, and that the volcanoes last erupted around 35,000 years ago. In addition they may account for a mysterious spike in oceanic
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
concentrations around 35,000 years ago. Methane forms naturally alongside the petroleum underneath the structure, and while petroleum flows have long abated, some residual methane continues to bubble up. This burst of methane would have caused a rapid increase in the population of methane-eating bacteria, which in turn caused a decrease in oxygen in the water, possibly causing a
dead zone Dead zone may refer to: Science and technology * Dead zone (cell phone), an area where cell phones cannot transmit to a nearby cell site * Dead zone (ecology), low-oxygen areas in the world's oceans * Dead band, the region of insensitivity of a ...
, in addition to the large amounts of crude oil released into the environment. The presence of these structures provides a hard surface on which life can grow, as the surrounding ocean floor is generally muddy. This is similar to what happens on
seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...
s, resulting in their place as an ecological "hub."


Onshore "tar volcanoes"

Onshore "tar volcanoes" have also been observed, for instance in
Carpinteria, California Carpinteria (; , meaning "Carpentry") is a small seaside city in southeastern Santa Barbara County, California. Located on the Central Coast (California), Central Coast of California, it had a population of 13,264 at the 2020 United States cens ...
, in an asphalt mine. Asphalt exuded from joint cracks in the upturned Monterey shale forming the floor of the mine.Plate 3-A in U.S. Geological Survey. Bulletin 321. 1907 Similar structures, the
Carpinteria Tar Pits The Carpinteria Tar Pits (also Carpinteria Oil Seeps) are a series of natural asphalt lakes situated in the southern part of Santa Barbara County in southern California, US. The Carpinteria Tar Pits are a natural asphalt lake areas similar ...
, still form on the beach below Carpinteria.


See also

*
Mud volcano A mud volcano or mud dome is a landform created by the eruption of mud or Slurry, slurries, water and gases. Several geological processes may cause the formation of mud volcanoes. Mud volcanoes are not true Igneous rock, igneous volcanoes as th ...
*
Petroleum seep A petroleum seep is a place where natural liquid or gaseous hydrocarbons escape to the Earth's atmosphere and surface, normally under low pressure or flow. Seeps generally occur above either natural terrestrial or underwater petroleum accumu ...
*
Pitch Lake The Pitch Lake is the largest natural deposit of bitumen in the world, estimated to contain 10 million tons. It is located in Trinidad and Tobago, more specifically in La Brea in southwest Trinidad, within the Siparia Regional Corporation. The la ...
*
Pockmark (geology) Pockmarks are concave, crater-like depressions on seabeds that are caused by fluids (liquids and gasses) escaping and erupting through the seafloor. They can vary in size and have been found worldwide. Pockmarks were discovered off the coasts of N ...


References

{{commonscat, Asphalt volcanoes


External links


What is an asphalt volcano?
Mother Nature Network, 2014. Good photos.

NOAA Ocean Explorer, April 24, 2014 Seamounts Petroleum geology