Olympus Mons the -diameter Pangboche crater (). The craters are notable for being two of several suspected source areas for shergottites, the most abundant class of Martian meteorites. As a shield volcano, Olympus Mons resembles the shape of the large volcanoes making up the Hawaiian Islands. The edifice is about wide. Because the mountain is so large, with complex structure at its edges, allocating a height to it is difficult. Olympus Mons stands above the Mars global datum, and its local relief, from the foot of the cliffs which form its northwest margin to its peak, is nearly (a little over twice
Olympus Mons gradient and residual heat from the volcano's magma chamber. Potential springs or seeps around the volcano would offer exciting possibilities for detecting microbial life. Olympus Mons and a few other volcanoes in the Tharsis region stand high enough to reach above the frequent Martian dust-storms recorded by telescopic observers as early as the 19th century. The astronomer Patrick Moore pointed out that Schiaparelli (1835–1910) "had found that his "Nodus Gordis" and "Olympic Snow" [Nix Olympica] were almost the only features to be seen" during dust storms, and "guessed correctly that they must be high". The Mariner 9 spacecraft arrived in