), Iceland, 2023 A volcano needs a reservoir of molten magma (e.g. a
magma chamber), a conduit to allow magma to rise through the crust, and a vent to allow the magma to escape above the surface as lava. The erupted volcanic material (lava and tephra) that is deposited around the vent is known as a '''''', typically a volcanic cone or mountain. The most common perception of a volcano is of a
conical mountain, spewing
lava and poisonous
gases from a
crater at its summit; however, this describes just one of the many types of volcano. The features of volcanoes are varied. The structure and behaviour of volcanoes depend on several factors. Some volcanoes have rugged peaks formed by
lava domes rather than a summit crater while others have
landscape features such as massive
plateaus. Vents that issue volcanic material (including lava and
ash) and gases (mainly steam and magmatic gases) can develop anywhere on the
landform and may give rise to smaller cones such as
Puu Ōō on a flank of
Kīlauea in Hawaii.
Volcanic craters are not always at the top of a mountain or hill and may be filled with lakes such as with
Lake Taupō in New Zealand. Some volcanoes can be low-relief landform features, with the potential to be hard to recognize as such and be obscured by geological processes. Other types of volcano include
mud volcanoes, which are structures often not associated with known magmatic activity; and
cryovolcanoes (or ice volcanoes), particularly on some moons of
Jupiter,
Saturn, and
Neptune. Active mud volcanoes tend to involve temperatures much lower than those of
igneous volcanoes except when the mud volcano is actually a vent of an igneous volcano.
Fissure vents fissure vent in
Iceland, the source of the
major world climate alteration of 1783–84, has a chain of volcanic cones along its length.
Volcanic fissure vents are generally found at
diverging plate boundaries, they are flat, linear fractures through which
basaltic lava emerges. These kinds of volcanoes are non-explosive and the basaltic lava tends to have a low viscosity and solidifies slowly leading to a gentle sloping basaltic
lava plateau. They often relate or constitute shield volcanoes
Olympus Mons, an extinct martian shield volcano is the largest known volcano in the
Solar System.
Lava domes Lava domes, also called dome volcanoes, have steep convex sides built by slow eruptions of highly viscous lava, for example,
rhyolite. Cinder cones may form as
flank vents on larger volcanoes, or occur on their own.
Parícutin in Mexico and
Sunset Crater in
Arizona are examples of cinder cones. In
New Mexico,
Caja del Rio is a
volcanic field of over 60 cinder cones. Based on satellite images, it has been suggested that cinder cones might occur on other terrestrial bodies in the Solar system too; on the surface of Mars and the Moon.
Stratovolcanoes (composite volcanoes) (vertical scale is exaggerated): Stratovolcanoes are tall conical mountains composed of lava flows and
tephra in alternate layers, the
strata that gives rise to the name. They are also known as
composite volcanoes because they are created from multiple structures during different kinds of eruptions; the main conduit bringing magma to the surface branches into multiple secondary conduits and occasional
laccoliths or
sills, the branching conduits may form
parasitic cones on the flanks of the main cone. Large pieces of tephra are called
volcanic bombs. Big bombs can measure more than across and weigh several tons.
Supervolcanoes , New Zealand. A supervolcano is defined as a volcano that has experienced one or more eruptions that produced over of volcanic deposits in a single explosive event. Such eruptions occur when a very large magma chamber full of gas-rich, silicic magma is emptied in a catastrophic
caldera-forming eruption. Ash flow
tuffs emplaced by such eruptions are the only volcanic product with volumes rivalling those of
flood basalts. Supervolcano eruptions, while the most dangerous type, are very rare;
four are known from the last million years, and about 60 historical VEI 8 eruptions have been identified in the geologic record over millions of years. A supervolcano can produce devastation on a continental scale, and severely cool global temperatures for many years after the eruption due to the huge volumes of
sulfur and ash released into the atmosphere. Because of the enormous area they cover, and subsequent concealment under vegetation and glacial deposits, supervolcanoes can be difficult to identify in the geologic record without careful
geological mapping. Known examples include
Yellowstone Caldera in
Yellowstone National Park and
Valles Caldera in
New Mexico (both western United States);
Lake Taupō in New Zealand;
Lake Toba in
Sumatra, Indonesia; and
Ngorongoro Crater in Tanzania.
Caldera volcanoes , a volcanic lake in
Oregon Volcanoes that, though large, are not large enough to be called supervolcanoes, may also form calderas (collapsed crater) in the same way. There may be active or dormant cones inside of the caldera or even a lake, such lakes are called
Volcanogenic lakes, or simply, volcanic lakes. In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above the ocean's surface. In the deep ocean basins, the tremendous weight of the water prevents the explosive release of steam and gases; however, submarine eruptions can be detected by
hydrophones and by the discoloration of water because of
volcanic gases.
Pillow lava is a common eruptive product of submarine volcanoes and is characterized by thick sequences of discontinuous pillow-shaped masses which form underwater. Even large submarine eruptions may not disturb the ocean surface, due to the rapid cooling effect and increased buoyancy in water (as compared to air), which often causes volcanic vents to form steep pillars on the ocean floor.
Hydrothermal vents are common near these volcanoes, and
some support peculiar ecosystems based on
chemotrophs feeding on dissolved minerals. Over time, the formations created by submarine volcanoes may become so large that they break the ocean surface as new islands or floating
pumice rafts. In May and June 2018, a multitude of
seismic signals were detected by earthquake monitoring agencies all over the world. They took the form of unusual humming sounds, and some of the signals detected in November of that year had a duration of up to 20 minutes. An
oceanographic research campaign in May 2019 showed that the previously mysterious humming noises were caused by the formation of a submarine volcano off the coast of
Mayotte.
Subglacial volcanoes Subglacial volcanoes develop underneath
ice caps. They are made up of lava plateaus capping extensive pillow lavas and
palagonite. These volcanoes are also called table mountains,
tuyas, or (in Iceland) mobergs. Very good examples of this type of volcano can be seen in Iceland and in
British Columbia. The origin of the term comes from
Tuya Butte, which is one of the several tuyas in the area of the
Tuya River and
Tuya Range in northern British Columbia. Tuya Butte was the first such
landform analysed and so its name has entered the geological literature for this kind of volcanic formation. The
Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of
Tuya Lake and south of the
Jennings River near the boundary with the
Yukon Territory.
Hydrothermal features Hydrothermal features, for example
geysers,
fumaroles,
mud pools,
mud volcanoes,
hot springs and acidic hot springs involve water as well as geothermal or magmatic activity. Such features are common around volcanoes and are often indicative of volcanism.
Mud volcanoes Mud volcanoes or mud domes are conical structures created by eruption of liquids and gases, particularly mud (slurries), water and gases, although several activities may contribute. The largest mud volcanoes are in diameter and reach high. Mud volcanoes can be seen off the shore of
Indonesia, on the island of
Baratang, in
Balochistan and in central Asia.
Fumarole Fumaroles are vents on the surface from which hot steam and volcanic gases erupt due to the presence of superheated groundwater, these may indicate volcanic activity. Fumaroles erupting sulfurous gases are also often called solfataras. ==Erupted material==