geology of mars volcanic image
  The Tharsis Bulge
Shield Volcanos
Lava Plains
Identifying Plains

How Are Lava Plains Identified?
Another sign indicating the volcanic origin of a plain is the existence of volcanic cones on the plain (Figure 6.17). In the middle of this image, there is a cone about 4 km across with an elongated caldera.

figure 6.17 figure 6.18

Small cones with a summit pit can also be found on other lava plains (Figure 6.18) . Most of the cones in this photo are about 500 m (or 1/3 mile) across. Their linear alignment may be related to the fault system of the area. Exactly how they formed is not known. Viscosity of the lava might also play a role in their formation.

Contrasts of surface smoothness can be diagnostic also (Figure 6.19) . Some experience may be required to delineate the origin of different smooth surfaces. The existence of wrinkle ridges may also be indicative because it takes a harder surface (such as the ones formed by lava flows) to buckle to produce wrinkle ridges (Figure 6.20) .

 figure 6.19 figure 6.20

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geology of mars