Giant Shield Volcanoes
Overview
The giant shield volcanoes on Mars are truly huge. The largest are three
times as high as the biggest Earth volcanoes. They also are bigger in
diameter. Thus, the biggest volcano on Mars is comparable to a pile of
nearly 100 Hawaiian volcanoes. Despite this difference in size, the Mars
shields look a lot like shield volcanoes on Earth. Both have the same
broad flat profiles, large central calderas, and similar lava flow
features. The giant martian shields are also much older than any Earth
volcano. The youngest lavas on the martian shields are about 20 to 200
million years old. The oldest lavas are near 2.5 billion years old. Thus,
these giant volcanoes were active for billions of years. This may explain
their large size. On Earth, plate tectonics is always moving volcanoes
away from their magma sources. Such movements are very slow, but they mean
that most Earth volcanoes have distinct lifetimes. In the Hawaiian
islands, for instance, volcanism lasts fo only a few million years on
any given island. In contrast, the lack of plate tectonics on Mars allowed
volcanoes to just keep growing. The only limit on their final size was the
volume of lavas available.
Size Comparison
Olympus Mons from Orbit
Olympus Mons 3D View
Olympus Mons Caldera
Tharsis Montes
Elysium Mons
Olympus Mons