Volcanism has played a major part in shaping not only planet Earth, but other places in our universe. Though other planets show signs of volcanic eruptions, most seemed to have erupted in the distant past and are inactive now. Both Mars and Venus have volcanoes much larger than any on Earth, and they have erupted huge amounts of lava onto their surfaces in the past.
Many of Mercury's basins contain smooth plains, like the lunar mare, that are believed likely to be filled with lava flows. Collapse structures possibly indicative of volcanism have been found in some craters. Eleven volcanic domes were identified in Mariner 10 images, including a 7-km high dome near the centre of Odin Planitia.
Odin Planitia is a large basin on Mercury located in the Tolstoj quadrangle at 23.3° N, 171.6° W. It was named after the Norse god Odin in 1976 by the IAU. A large volcanic dome 7 km in diameter and 1.4 km high is situated near the center of Odin.
The surface of Venus is dominated by volcanism and has produced more volcanoes than any other planet in the solar system. It has a surface that is 90% basalt, and about 80% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface.
The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Even though there are over 1,600 major volcanoes on Venus, none is known to be erupting at present and most are probably long extinct. However, radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus's highest volcano Maat Mons, in the form of ash flows near the summit and on the northern flank.
Although many lines of evidence suggest that Venus is likely to be volcanically active, present-day eruptions at Maat Mons have not been confirmed.
In April 2010, Suzanne E. Smrekar et al. announced the discovery of three active volcanoes, which suggests that Venus is periodically resurfaced by lava flows.
Venus contains shield volcanoes, widespread lava flows and some unusual volcanoes called pancake domes and "tick-like" structures which are not present on Earth. Pancake dome volcanoes are up to 15 km (9.3 mi) in diameter and less than 1 km (0.62 mi) in height and are 100 times larger than those formed on Earth. They are usually associated with coronae and tesserae (large regions of highly deformed terrain, folded and fractured in two or three dimensions, believed to be unique to Venus). The pancakes are thought to be formed by highly viscous, silica-rich lava erupting under Venus's high atmospheric pressure.
The "tick-like" structures are called scalloped margin domes. They are commonly called ticks because they appear as domes with numerous legs. They are thought to have undergone mass wasting events such as landslides on their margins. Sometimes deposits of debris can be seen scattered around them.
On Earth, volcanoes are mainly of two types: shield volcanoes and composite or stratovolcanoes. The shield volcanoes, for example those in Hawaii, eject magma from the depths of the Earth in zones called hot spots. The lava from these volcanos is relatively fluid and permits the escape of gases. Composite volcanos, such as Mount Saint Helens and Mount Pinatubo, are associated with tectonic plates. In this type of volcano, the oceanic crust of one plate is sliding underneath the other in a subduction zone, together with an inflow of seawater, producing a gummier lava that restricts the exit of the gases, and for that reason, composite volcanoes tend to erupt more violently.
On Venus, where there are no tectonic plates or seawater, volcanoes are mostly of the shield type. Nevertheless, the morphology of volcanoes on Venus is different: on Earth, shield volcanoes can be a few tens of kilometres wide and up to 10 km (6.2 mi) high in the case of Mauna Kea, measured from the sea floor. On Venus, these volcanoes can cover hundreds of kilometres in area, but they are relatively flat, with an average height of 1.5 km (0.93 mi).
Other unique features of Venus's surface are novae (radial networks of dikes or grabens) and arachnoids. A nova is formed when large quantities of magma are extruded onto the surface to form radiating ridges and trenches which are highly reflective to radar. These dikes form a symmetrical network around the central point where the lava emerged, where there may also be a depression caused by the collapse of the magma chamber.
Arachnoids are so named because they resemble a spider's web, featuring several concentric ovals surrounded by a complex network of radial fractures similar to those of a nova. It is not known whether the 250 or so features identified as arachnoids actually share a common origin, or are the result of different geological processes.
List of Volcanoes
The Earth's Moon has no large volcanoes. However, vast plains of basaltic lavas cover much of the lunar surface. The earliest astronomers thought, wrongly, that these 'Plains were seas of lunar water'. Thus, they were called "mare " (pronounced "mahr-ay"). Mare means "sea" in Latin. In addition, other volcanic features also occur within the lunar mare. The most important are sinuous rilles , dark mantling deposits, and small volcanic domes and cones . Most of these features are fairly small, however. They form only a tiny fraction of the lunar volcanic record.
List of Volcanoes
Scientists have never recorded an active volcano eruption on the surface of Mars, however, the European Space Agency's Mars Express orbiter photographed lava flows that must have occurred within the past two million years, suggesting a relatively recent geologic activity.
Volcanic activity, or volcanism, has played a significant role in the geologic evolution of Mars. Scientists have known since the Mariner 9 mission in 1972 that volcanic features cover large portions of the Martian surface. These features include extensive lava flows, vast volcanic plains, and the largest known volcanoes in the Solar System. Martian volcanic features range in age from Noachian (>3.7 billion years) to late Amazonian (< 500 million years), indicating that the planet has been volcanically active throughout its history and probably still is so today.
Volcanic plains are widespread on Mars. Two types of plains are commonly recognized: those where lava flow features are common, and those where flow features are generally absent but a volcanic origin is inferred by other characteristics.
Plains with abundant lava flow features occur in and around the large volcanic provinces of Tharsis and Elysium.
Flow features include both sheet flow and tube- and channel-fed flow morphologies. Sheet flows show complex, overlapping flow lobes and may extend for many hundreds of kilometers from their source areas.
Lava flows can form a lava tube when the exposed upper layers of lava cool and solidify to form a roof while the lava underneath continues flowing. Often, when all the remaining lava leaves the tube, the roof collapses to make a channel or line of pit craters (catena).
An unusual type of flow feature occurs in the Cerberus plains south of Elysium and in Amazonis. These flows have a broken platey texture, consisting of dark, kilometer-scale slabs embedded in a light-toned matrix. They have been attributed to rafted slabs of solidified lava floating on a still-molten subsurface. Others have claimed the broken slabs represent pack ice that froze over a sea that pooled in the area after massive releases of groundwater from the Cerberus Fossae area.
Both Earth and Mars are large, differentiated planets built from similar chondritic materials. Many of the same magmatic processes that occur on Earth also occur on Mars, and both planets are similar enough compositionally that the same names can be applied to their igneous rocks and minerals.
Volcanism is a process in which magma from a planet¹s interior rises through the crust and erupts on the surface. The erupted materials consist of molten rock (lava), hot fragmental debris (tephra or ash), and gases. Volcanism is a principal way that planets release their internal heat. Volcanic eruptions produce distinctive landforms, rock types, and terrains that provide a window on the chemical composition, thermal state, and history of a planet's interior.
Magma is a complex, high-temperature mixture of molten silicates, suspended crystals, and dissolved gases. Magma on Mars likely ascends in a similar manner to that on Earth. It rises through the lower crust in diapiric bodies that are less dense than the surrounding material. As the magma rises, it eventually reaches regions of lower density.
When the magma density matches that of the host rock, buoyancy is neutralized and the magma body stalls. At this point, it may form a magma chamber and spread out laterally into a network of dikes and sills. Subsequently, the magma may cool and solidify to form intrusive igneous bodies (plutons). Geologists estimate that about 80% of the magma generated on Earth stalls in the crust and never reaches the surface.
As magma rises and cools, it undergoes many complex and dynamic compositional changes. Heavier minerals may crystallize and settle to the bottom of the magma chamber. The magma may also assimilate portions of host rock or mix with other batches of magma. These processes alter the composition of the remaining melt, so that any magma reaching the surface may be chemically quite different from its parent melt.
Magmas that have been so altered are said to be "evolved" to distinguish them from "primitive" magmas that more closely resemble the composition of their mantle source. (See igneous differentiation and fractional crystallization.) More highly evolved magmas are usually felsic, that is enriched in silica, volatiles, and other light elements compared to iron- and magnesium-rich (mafic) primitive magmas.
The degree and extent to which magmas evolve over time is an indication of a planet's level of internal heat and tectonic activity. The Earth's continental crust is made up of evolved granitic rocks that developed through many episodes of magmatic reprocessing. Evolved igneous rocks are much less common on cold, dead bodies such as the Moon. Mars, being intermediate in size between the Earth and the Moon, is thought to be intermediate is its level of magmatic activity.
At shallower depths in the crust, the lithostatic pressure on the magma body decreases. The reduced pressure can cause gases (volatiles), such as carbon dioxide and water vapor, to exsolve from the melt into a froth of gas bubbles. The nucleation of bubbles causes a rapid expansion and cooling of the surrounding melt, producing glassy shards that may erupt explosively as tephra (also called pyroclastics).
Fine-grained tephra is commonly referred to as volcanic ash. Whether a volcano erupts explosively or effusively as fluid lava depends on the composition of the melt. Felsic magmas of andesitic and rhyolitic composition tend to erupt explosively. They are very viscous (thick and sticky) and rich in dissolved gases. Mafic magmas, on the other hand, are low in volatiles and commonly erupt effusively as basaltic lava flows.
However, these are only generalizations. For example, magma that comes into sudden contact with groundwater or surface water may erupt violently in steam explosions called hydromagmatic (phreatomagmatic or phreatic) eruptions. Also, erupting magmas may behave differently on planets with different interior compositions, atmospheres, and gravity fields.
The most common form of volcanism on the Earth is basaltic. Basalts are extrusive igneous rocks derived from the partial melting of the upper mantle. They are rich in iron and magnesium (mafic) minerals and commonly dark gray in color. The principal type of volcanism on Mars is almost certainly basaltic too.
On Earth, basaltic magmas commonly erupt as highly fluid flows, which either emerge directly from vents or form by the coalescence of molten clots at the base of fire fountains (Hawaiian eruption). These styles are also common on Mars, but the lower gravity and atmospheric pressure on Mars allow nucleation of gas bubbles to occur more readily and at greater depths than on Earth.
As a consequence, Martian basaltic volcanoes are also capable of erupting large quantities of ash in Plinian-style eruptions. In a Plinian eruption, hot ash is incorporated into the atmosphere, forming a huge convective column (cloud). If insufficient atmosphere is incorporated, the column may collapse to form pyroclastic flows. Plinian eruptions are rare in basaltic volcanoes on Earth where such eruptions are most commonly associated with silica-rich andesitic or rhyolitic magmas (e.g., Mount St. Helens).
Because the lower gravity of Mars generates less buoyancy forces on magma rising through the crust, the magma chambers that feed volcanoes on Mars are thought to be deeper and much larger than those on Earth. If a magma body on Mars is to reach close enough to the surface to erupt before solidifying, it must be big. Consequently, eruptions on Mars are less frequent than on Earth, but are of enormous scale and eruptive rate when they do occur. Somewhat paradoxically, the lower gravity of Mars also allows for longer and more widespread lava flows. Lava eruptions on Mars may be unimaginably huge. A vast lava flow the size of the state of Oregon has recently been described in western Elysium Planitia. The flow is believed to have been emplaced turbulently over the span of several weeks and thought to be one of the youngest lava flows on Mars.
The tectonic settings of volcanoes on Earth and Mars are very different. Most active volcanoes on Earth occur in long, linear chains along plate boundaries, either in zones where the lithosphere is spreading apart (divergent boundaries) or being subducted back into the mantle (convergent boundaries).
Because Mars currently lacks plate tectonics, volcanoes there do not show the same global pattern as on Earth. Martian volcanoes are more analogous to terrestrial mid-plate volcanoes, such as those in the Hawaiian Islands, which are thought to have formed over a stationary mantle plume.
The largest and most conspicuous volcanoes on Mars occur in Tharsis and Elysium regions. These volcanoes are strikingly similar to shield volcanoes on Earth. Both have shallow-sloping flanks and summit calderas. The main difference between Martian shield volcanoes and those on Earth is in size: Martian shield volcanoes are truly colossal. For example, the tallest volcano on Mars, Olympus Mons, is 550 km across and 21 km high.
It is nearly 100 times greater in volume than Mauna Loa in Hawaii, the largest shield volcano on Earth. Geologists think one of the reasons that volcanoes on Mars are able to grow so large is because Mars lacks plate tectonics. The Martian lithosphere does not slide over the upper mantle (asthenosphere) as on Earth, so lava from a stationary hot spot is able to accumulate at one location on the surface for a billion years or longer.
Olympus Mons is the youngest and tallest large volcano on Mars. It is located 1200 km northwest of of the Tharsis Montes, just off the western edge of the Tharsis bulge. Its summit is 21 km above datum (Mars "sea" level) and has a central caldera complex consisting of six nested calderas that together form a depression 72 x 91 km wide and 3.2 km deep.
As a shield volcano, it has an extremely low profile with shallow slopes averaging between 4-5 degrees. The volcano was built up by many thousands of individual flows of highly fluid lava. An irregular escarpment, in places up to 8 km tall, lies at the base of the volcano, forming a kind of pedestal on which the volcano sits. At various locations around the volcano, immense lava flows can be seen extending into the adjacent plains, burying the escarpment. In medium resolution images (100 m/pixel), the surface of the volcano has a fine radial texture due to the innumerable flows and leveed lava channels that line its flanks.
Volcanoes on Mars
Interesting Images
Neighboring volcanoes on Mars PhysOrg - April 4, 2011
ESA¹s Mars Express has returned images of mist-capped volcanoes located in the northern hemisphere of the red planet. Long after volcanic activity ceased, the area was transformed by meteor impacts that deposited ejected material over the lower flanks of the volcanoes.
Volcanism on Io, a moon of Jupiter, produces lava flows, volcanic pits, and plumes of sulfur and sulfur dioxide hundreds of kilometres high. This volcanic activity was discovered in 1979 by Voyager 1 imaging scientists.
Observations of Io by passing spacecraft (the Voyagers, Galileo, Cassini, and New Horizons) and Earth-based astronomers have revealed more than 150 active volcanoes. Up to 400 such volcanoes are predicted to exist based on these observations. Io's volcanism makes the satellite one of only five known currently volcanically active worlds in the solar system (the other four being Earth, Venus, Saturn's moon Enceladus, and Neptune's moon Triton).
First predicted shortly before the Voyager 1 flyby, the heat source for Io's volcanism comes from tidal heating produced by its forced orbital eccentricity. This differs from Earth's internal heating, which is derived primarily from radioactive isotope decay.
Io's eccentric orbit leads to a slight difference in Jupiter's gravitational pull on the satellite between its closest and farthest points on its orbit, causing a varying tidal bulge. This variation in the shape of Io causes frictional heating in its interior. Without this tidal heating, Io might have been similar to the Earth's moon, a world of similar size and mass, geologically dead and covered with numerous impact craters.
Io's volcanism has led to the formation of hundreds of volcanic centres and extensive lava formations, making the moon the most volcanically active body in the Solar System. Three different types of volcanic eruptions have been identified, differing in duration, intensity, lava effusion rate, and whether the eruption occurs within a volcanic pit (known as a patera). Lava flows on Io, tens or hundreds of kilometres long, have primarily basaltic composition, similar to lavas seen on Earth at shield volcanoes such as Kilauea in Hawaii.
While most lavas on Io are made of basalt, a few lava flows consisting of sulfur and sulfur dioxide have been seen. In addition, eruption temperatures as high as 1,600 K (1,300 °C; 2,400 °F) were detected, which can be explained by the eruption of high-temperature ultramafic silicate lavas.
As a result of the presence of significant quantities of sulfurous materials in Io's crust and on its surface, some eruptions propel sulfur, sulfur dioxide gas, and pyroclastic material up to 500 kilometres (310 mi) into space, producing large, umbrella-shaped volcanic plumes.
This material paints the surrounding terrain in red, black, and/or white, and provides material for Io's patchy atmosphere and Jupiter's extensive magnetosphere. Spacecraft that have flown by Io since 1979 have observed numerous surface changes as a result of Io's volcanic activity.
Volcanoes on Io, a moon of the planet Jupiter, are believed to eject sulfur or possibly sulfur dioxide.
Saturn's moon Enceladus has geysers that spew water which have been photographed erupting by NASA's Cassini-Huygens spacecraft.
Another moon of Saturn, Titan, may also be volcanic (which would explain the satellite's dense atmosphere), as may be Neptune's moon, Triton.
'Ice volcano' identified on Saturn's moon Titan BBC - December 15, 2010
Scientists think they now have the best evidence yet for an ice volcano on Titan, the largest moon of Saturn. The Cassini probe has spotted a 1,500m-high mountain with a deep pit in it, and what looks like a flow of material on the surrounding surface. The new feature, which has been dubbed "The Rose", was seen with the probe's radar and infrared instruments. Titan has long been speculated to have cryovolcanoes but its hazy atmosphere makes all observations very difficult.
Ice Volcano Found on Saturn Moon Titan Space.com - April 1, 2011
For the first time, scientists now have solid evidence for an ice volcano on Saturn's moon Titan, according to a new study.
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