A
pancake dome is an unusual type of
volcano found on the planet
Venus. They are widely scattered on that planet and often form groups or clusters, though with smaller numbers of pancake domes in each group than is typical for the more common
shield volcanos. They are commonly found near
coronae and
tesserae (large regions of highly deformed terrain, folded and fractured in two or three dimensions, believed to be unique to Venus) in the lowland plains. Pancake domes are between 10 and 100 times larger than volcanic domes formed on Earth.
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| Fotla Coronea |
Pancake domes have a broad, flat profile similar to shield volcanoes and are thought to form from one large, slow eruption of viscous
silica-rich
lava. They usually have a central pit- or bowl-like feature similar to a
volcanic crater, but it is thought that these pits form after the eruption as the lava cools and emits gas rather than being a
vent from which the lava originated. The surface of pancake domes are covered with patterns of small cracks and faults.
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Radar mosaic of two 65-km-wide (and less than 1-km-high)
pancake domes in Venus's Eistla region
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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
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Computer-generated perspective view of
pancake domes in Venus's Alpha Regio |
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 kilometers (9 mi) in diameter and less than 1 kilometer (0.6 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.
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 of the shield type. Nevertheless, the morphology of the volcanos of Venus is different: on the Earth, shield volcanoes can be a few tens of kilometres wide and up to 10 kilometres high (6.2 mi) in the case of
Mauna Kea, measured from the sea floor. On Venus, these volcanos can cover hundreds of kilometres in area, but they are relatively flat, with an average height of 1.5 kilometres (0.9 mi).
