Asphalt volcanoes are a rare variety of submarine volcano (seamount). They were unknown before 2003. Several examples have been found along the coasts of the United States and Mexico and elsewhere, some still showing activity. [1] Asphalt volcanoes resemble other seamounts however they are made entirely of asphalt. The structures are thought to form above geologic faults through which petroleum seeps from deeper in the Earth's crust.
Asphalt volcanoes are vents on the ocean floor through which asphalt erupts rather than of lava. They were discovered in the Gulf of Mexico 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. [2]
The first asphalt volcanoes were discovered in 2003 by a research expedition to the Gulf of Mexico. [2] They are located on a seafloor hill named "Chapopote," Nahuatl for "tar." The site is located in a field of salt domes 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 20 m (66 ft) across. Also discovered alongside the asphalt were areas soaked with petroleum and methane hydrate, 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. [3]
One hypothesis is that he tar is relatively hot when it comes out of the seafloor, but just like undersea lava flows, it is quickly cooled by the much colder seawater around it. [2] This produces forms similar to the distinctive A'a and pahoehoe types of basalt lava flow seen in places like Hawaii. 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 in phreatomagmatic eruptions. [3]
The team proposed an asphalt volcano formation theory in a paper published in Eos . [2] [4] The article suggested that water heated past the critical point underneath the seafloor found a passageway to the surface, most likely a salt dome, and carried with it a heavy load of hydrocarbons 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 smokers. Once the water reaches the surface, it cools, and its carrying capacity drops. [2] 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. [3]
The role of temperature in asphalt volcanism is debated, with evidence suggesting asphalt does not erupt in a hot state. Instead, the pāhoehoe-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 [5] [6] .
In 2007, seven more such structures were discovered off the coast of Santa Barbara, California. The largest of these domes lies at a depth of 700 ft (213 m). 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 by a team led by David Valentine in 2007, utilizing DSV Alvin . Samples were brought up for testing at the university campus and the Woods Hole Oceanographic Institution. [7]
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 puts the structures at between 30 and 40 thousand years old. They had at one time been a prolific source of methane. The two largest structures, less than 1 km (1 mi) 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. [7] 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. [However] the 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. [1]
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 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. [2] 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, in addition to the large amounts of crude oil released into the environment. [1]
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 seamounts, resulting in their place as an ecological "hub." [1]
Onshore "tar volcanoes" have also been observed, for instance in Carpinteria, California, in an asphalt mine. Asphalt exuded from joint cracks in the upturned Monterey shale forming the floor of the mine. [8] Similar structures, the Carpinteria Tar Pits, still form on the beach below Carpinteria.
A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface, and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 m (3,300–13,100 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 m (3,281 ft) above the seafloor, characteristically of conical form. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface. After they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts".
Tar pits, sometimes referred to as asphalt pits, are large asphalt deposits. They form in the presence of petroleum, which is created when decayed organic matter is subjected to pressure underground. If this crude oil seeps upward via fractures, conduits, or porous sedimentary rock layers, it may pool up at the surface. The lighter components of the crude oil evaporate into the atmosphere, leaving behind a black, sticky asphalt. Tar pits are often excavated because they contain large fossil collections.
A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid lava, which travels farther and forms thinner flows than the more viscous lava erupted from a stratovolcano. Repeated eruptions result in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form.
A cold seep is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. Cold does not mean that the temperature of the seepage is lower than that of the surrounding sea water. On the contrary, its temperature is often slightly higher. The "cold" is relative to the very warm conditions of a hydrothermal vent. Cold seeps constitute a biome supporting several endemic species.
The fifteen volcanoes that make up the eight principal islands of Hawaii are the youngest in a chain of more than 129 volcanoes that stretch 5,800 kilometers (3,600 mi) across the North Pacific Ocean, called the Hawaiian–Emperor seamount chain. Hawaiʻi's volcanoes rise an average of 4,600 meters (15,000 ft) to reach sea level from their base. The largest, Mauna Loa, is 4,169 meters (13,678 ft) high. As shield volcanoes, they are built by accumulated lava flows, growing a few meters or feet at a time to form a broad and gently sloping shape.
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 alone are estimated to account for 75% of the magma output on Earth. Although most submarine volcanoes are located in the depths of seas and oceans, some also exist in shallow water, and these can discharge material into the atmosphere during an eruption. The total number of submarine volcanoes is estimated to be over one million of which some 75,000 rise more than 1 kilometre (0.62 mi) above the seabed. Only 119 submarine volcanoes in Earth's oceans and seas are known to have erupted during the last 11,700 years.
The Juan de Fuca Ridge is a mid-ocean spreading center and divergent plate boundary located off the coast of the Pacific Northwest region of North America, named after Juan de Fuca. The ridge separates the Pacific Plate to the west and the Juan de Fuca Plate to the east. It runs generally northward, with a length of approximately 500 kilometres (310 mi). The ridge is a section of what remains from the larger Pacific-Farallon Ridge which used to be the primary spreading center of this region, driving the Farallon Plate underneath the North American Plate through the process of plate tectonics. Today, the Juan de Fuca Ridge pushes the Juan de Fuca Plate underneath the North American plate, forming the Cascadia Subduction Zone.
Several types of volcanic eruptions—during which material is expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.
Axial Seamount is a seamount, submarine volcano, and underwater shield volcano in the Pacific Ocean, located on the Juan de Fuca Ridge, approximately 480 km (298 mi) west of Cannon Beach, Oregon. Standing 1,100 m (3,609 ft) high, Axial Seamount is the youngest volcano and current eruptive center of the Cobb–Eickelberg Seamount chain. Located at the center of both a geological hotspot and a mid-ocean ridge, the seamount is geologically complex, and its origins are still poorly understood. Axial Seamount is set on a long, low-lying plateau, with two large rift zones trending 50 km (31 mi) to the northeast and southwest of its center. The volcano features an unusual rectangular caldera, and its flanks are pockmarked by fissures, vents, sheet flows, and pit craters up to 100 m (328 ft) deep; its geology is further complicated by its intersection with several smaller seamounts surrounding it.
The Cobb-Eickelberg seamount chain is a range of undersea mountains formed by volcanic activity of the Cobb hotspot located in the Pacific Ocean. The seamount chain extends to the southeast on the Pacific Plate, beginning at the Aleutian Trench and terminating at Axial Seamount, located on the Juan de Fuca Ridge. The seamount chain is spread over a vast length of approximately 1,800 km. The location of the Cobb hotspot that gives rise to these seamounts is 46° N—130° W. The Pacific plate is moving to the northwest over the hotspot, causing the seamounts in the chain to decrease in age to the southeast. Axial is the youngest seamount and is located approximately 480 km west of Cannon Beach, Oregon. The most studied seamounts that make up this chain are Axial, Brown Bear, Cobb, and Patton seamounts. There are many other seamounts in this chain which have not been explored.
The Hawaiʻi 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 Hawaiian–Emperor seamount chain, a 6,200-kilometer (3,900 mi) mostly undersea volcanic mountain range. Four of these volcanoes are active, two are dormant; more than 123 are extinct, most now preserved as atolls or seamounts. The chain extends from south of the island of Hawaiʻi to the edge of the Aleutian Trench, near the eastern coast of Russia.
Detroit Seamount, which was formed around 76 million years ago, is one of the oldest seamounts of the Hawaiian-Emperor seamount chain. It lies near the northernmost end of the chain and is south of Aleutian Islands, at 51°28.80′N167°36′E
The following outline is provided as an overview of and introduction to Oceanography.
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from 800 to 1,200 °C. The volcanic rock resulting from subsequent cooling is also often called lava.
Koko Guyot is a 48.1-million-year-old guyot, a type of underwater volcano with a flat top, which lies near the southern end of the Emperor seamounts, about 200 km (124 mi) north of the "bend" in the volcanic Hawaiian-Emperor seamount chain. Pillow lava has been sampled on the north west flank of Koko Seamount, and the oldest dated lava is 40 million years old. Seismic studies indicate that it is built on a 9 km (6 mi) thick portion of the Pacific Plate. The oldest rock from the north side of Koko Seamount is dated at 52.6 and the south side of Koko at 50.4 million years ago. To the southeast of the bend is Kimmei Seamount at 47.9 million years ago and southeast of it, Daikakuji at 46.7.
The Campeche Knolls are diapirs rising from a salt deposit in the southern Gulf of Mexico, separated from the Mississippi-Texas-Louisiana salt province by the Sigsbee Abyssal Plain. Located southeast of the Sigsbee Knolls, the Campeche Knolls are bounded by Campeche Bank to the East, the Bay of Campeche to the South, and the salt-free abyssal plain called the Veracruz Tongue to the West. Salt deposition is inferred to have occurred in the Late Jurassic, during the rifting stage of the gulf, equivalent to the Louann Salt of the Texas-Louisiana slope. Multibeam echosounder images collected during R/V Sonne cruise SO174 show the northern Campeche Knolls as distinct, elongated hills that average 3 by 6 mi in size, with reliefs of 1,475 to 2,625 ft and slopes of 10 to 20 percent.
Macdonald seamount is a seamount in Polynesia, southeast of the Austral Islands and in the neighbourhood of a system of seamounts that include the Ngatemato seamounts and the Taukina seamounts. It rises 4,200 metres (13,800 ft) from the seafloor to a depth of about 40 metres (130 ft) and has a flat top, but the height of its top appears to vary with volcanic activity. There are some subsidiary cones such as Macdocald seamount. The seamount was discovered in 1967 and has been periodically active with gas release and seismic activity since then. There is hydrothermal activity on Macdonald, and the vents are populated by hyperthermophilic bacteria.
NOASS Okeanos Explorer Gulf of Mexico 2017 Expedition was the first of three expeditions on the NOAAS Okeanos Explorer intended to increase the understanding of the deep-sea environment in the Gulf of Mexico. Gulf of Mexico 2017 was a 23-day telepresence-enabled expedition focused on acquiring data on priority exploration areas identified by ocean management and scientific communities. The goal of the expedition was to use remotely operated vehicle (ROV) dives and seafloor mapping operations to increase the understanding of the deep-sea ecosystems in these areas to support management decisions. Many of the areas had no sonar data, these areas were top priority for high-resolution bathymetry collection. The expedition established a baseline of information in the region to catalyze further exploration, research, and management activities. The expedition lasted from 29 November 2017 to 21 December 2017.
Not to be confused with pingo landforms.
South Arch volcanic field is an underwater volcanic field south of Hawaiʻi Island. It was active during the last 10,000 years, and covers an area of 35 by 50 kilometres at a depth of 4,950 metres (16,240 ft).