Another volcanic area is called the Elysium, close to the Viking II landing site (Figure 6.7) . This area is characterized by three large volcanos. Both the Tharsis and the Elysium regions are located on top of a crustal swell. This suggests that they might be a result of some thermal processes within the Martian interior that caused surface uplift in these areas and produced magma extrusions.

Mantle up-welling such as the illustration given in Figure 6.8 can be a plausible mechanism for the origin of these volcanos. Most of the shield volcanos in Elysium share similar morphological features with the Olympus Mons, except that they are smaller in size. Generally, they are relatively young features, as evidenced by the lack of impact craters. Olympus Mons is estimated to be as young as 200 million years. If it is true, when Olympus Mons last erupted, dinosaurs were still roaming on the surface of the Earth.

In addition to volcanos in these two areas, smaller volcanic shields are scattered all over the planet. Biblis (Figure 6.9) and Ulysses (Figure 6.10) are two examples. They are indeed smaller shields (both about 100 km across). On the other hand, because of their relatively large caldera, some scientists suggest that they could be the remnant of buried larger shield volcanos.

A 3-dimensional view of Ulysses has been reconstructed (Figure 6.11) . This 3D view clearly shows the low dooming profile of this volcano.