Volcanoes and Geology
Volcanoes and Geology
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Mars is roughly half
the size of Earth, despite the fact that it contains several volcanoes that
are many times larger than the ones on Earth. On Earth volcanoes are created
during the process of plate tectonics. Mars has no current plate tectonics,
which suggests that Mars' volcanoes are ancient. The lack of plate tectonics
explains why Mars is |
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The paterae (patera means "saucer" in Latin) are widely varied in form. In general they have very shallow slopes and scalloped, complex edges in their summit calderas; many have radial channels on their flanks. Some of the paterae (for example, Apollinaris Patera) have been extensively modified by collapse and erosion; others (Biblis Patera, for example) have a fairly symmetric structure with collapsed caldera walls. The speculation is that, because of their susceptibility to erosion and collapse, they are composed of loose materials such as ash flows. The extreme state of erosion on some of the paterae leads to the conclusion that these are the oldest of the volcanic constructs. |
The Tharsis Region: | |
The cluster of four large spots found in the northern
hemisphere of Mars are referred to as the Tharsis Ridge The most amazing of these giant
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The Elysium Plains: | |
The Elysium area of Mars
seems to contain some of the oldest volcanoes on Mars. We can tell this
because the lava flows in these plains are heavily cratered, meaning that
they have had more time on the surface or have been exposed longer.
The two larget volcanoes in this area are Hecates Tholus and
Elysium Mons. They are about the size of our Earth's  volcanoes. On the bottom right is a computer generated view of
Elysium Mons from the base of the volcano. Elysium Mons is one of the steepest
sloping montes on Mars. This volcano is much smaller than the Tharsis volcanoes.
It is only 9 km tall, and is about 240 km in diameter. So, it is nearly
the same size as the largest Hawaiian volcano. Like the Tharsis Montes,
however, Elysium Mons sits on a large pile of lava flows. This lets it rise
12 km above the mean planetary elevation. It grades so smoothly into the
surrounding lava plains that its base is hard to see. Above, on the left
is a view of the Elysium volcanic region. Click here
to see a larger version, and here to see an even
larger version. The top volcano is Hecates Tholus, the middle one is
Elysium Mons, and the bottom one is Albor Tholus. |
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Slit Volcano In Tempe Terra (Top) | |
Slit Volcano with Dunes (Left) | |
New Volcano Images from Mars Global Surveyor | |
only a little
more than half the size of Earth (see the 
The montes or large shields are likely
basaltic (like the volcanoes in Hawaii and Iceland), very large (
The tholi are smaller than the montes,
generally convex (dome-shaped), and have somewhat steeper sides, in some
cases greater than 8 degrees in slope. There are two possible explanations
for the difference between the tholi and the montes. It may be that the
material of the tholi was more fluid and flowing during the eruptions, or
it may be because the eruptions that formed the tholi were of small volume,
and hence the flows piled up closer to their source. 
or Bulge. It's called that because it is an area that
literally bulges out of the surrounding plains. Some scientists think this
was created by internal faults letting lava leak through to the surface
which created the numerous volcanoes in that region. It is an area of Mars
that was once bursting with volcanic activity. The area consists of four
massive volcanoes. The large volcano in upper left of the image is Olympus
Mons. The northern most volcano of the three aligned is Ascraeus Mons (11°N,
104°W). Moving south you will find Pavonis Mons (0° N, 133°W),
and then Arisa Mons (9°S, 120°W), in addition about 4 minor volcanoes:
Ulysses Patera, Biblis Patera, Ceranius Tholus, and Alba Patera. Tremendous
lava flow patterns can be seen at the base of the volcanoes, especially
Olympus Mons
volcanoes
is Olympus Mons (18°N, 133°W) which rises about 24km (15 miles)
above the surrounding plains. Its base is more than 500km (340 miles) in
diameter, and the north side is rimmed by a cliff 6km (4 miles) high. The
forces that caused abrupt cliff were glacial. About 3.8 billion years ago
it is estimated the the north pole of Mars was located to the south east
of Olympus Mons. Due to the shifting in the Martian crust that causes polar
wandering, the poles migrated they cut right through this volcano very easily.
On the north side of the base you can see glacial deposits at the base of
the cliff. At the caldera (peak or top) you can see several impact craters
that widened the mouth of the volcano. 
Alba Patera is unique among the
paterae on Mars and appears to be unlike any other feature in the solar
system. It is very large (over 1600 kilometers across), has a central caldera,
but rises no more than 3 km from the surrounding plains. Alba Patera appears
to have been formed by numerous flow events that were either much higher
in rate or much longer in duration than flows seen elsewhere. Alba Patera
is comparable to Olympus in size, horizontally, But, this volcano has been
so eroded over time no one will ever know if it was once comparable to the
great Olympus Mons.
