Page 43 - (DK) Eyewitness - Mars
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180˚ 90˚ 0˚ 270˚ 180˚ LANDS OF VOLCANISM
The main volcanic regions,
65˚ Olympus Mons Alba Patera Northern Plains Tharsis and Elysium, are in
yellow. The third, much smaller
Tharsis region Elysium region of pateras is near Hellas
Planitia. Volcanoes termed
“patera”—saucer-like, because
30˚ they are flat—are much older
than the volcanoes of Tharsis
and Elysium. Alba Patera has
the largest base—930 miles
0˚ (1,500 km) across—but is less
than 4.3 miles (7 km) high. The
entire Tharsis region is 2,500
miles (4,000 km) across.
30˚
Hellas
Planitia
65˚
180˚ 90˚ 0˚ 270˚ 180˚
Large shield volcanoes Highland paterae Volcanic plains
Smaller shield volcanoes Lava flows Larger craters or basins
Dome produced by
successive lava eruptions
Cooler rock
of crust MAGMA’S RISE
The Tharsis region was created by
“mantle convection.” This is an upward
circulation of underground molten
rock, or magma, from a hotter zone
beneath the mantle. Rising magma
Magma creates a hot spot on the crust
rises into where lava erupts. Magma here is
mantle rock red; cooler mantle rock is blue,
green, and yellow.
Mantle rock
FLOW OF FIRE AND WATER
In a painting of early Mars an artist pictures a lake at the foot of an erupting
volcano. A great plume of ash rises from the cone as molten lava flows toward
an inlet. Rock formations were formed by previous lava flows.
Various volcanoes
Some volcanoes erupt in explosions that throw out ash, gases, and rock that build
steep slopes, termed “flanks.” These slopes may be eroded by weather and cut by
new rushes of lava. Other volcanoes steadily release lava that cools into gentle
slopes shaped like a flattened dome or a shield. Most Martian volcanoes, like
Olympus Mons, are the shield type.
CERAUNIUS THOLUS
This steep volcanic cone was
likely built up by explosive
eruptions of porous volcanic
ash, which is easily eroded.
Later streams of upwelling
molten lava cut channels in
the cone’s sides, and
meteorites pocked it with
impact craters. Ceraunius HELLAS MOUNDS TYRRHENA PATERA APOLLINARIUS PATERA
Tholus is in the northern Mounds near Hellas The shallow, eroded slopes An initial ash eruption
Tharsis region, between Planitia may have been of this patera volcano may created the steep sides of
Alba Patera and the three caused by superheated be composed of ash this volcano. Later, molten
great shield volcanoes of mud rising explosively deposits instead of lava formed a fan on the
Tharsis Montes. to the surface. repeated lava flows. south flank.
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