FORMATION OF MARS' SURFACE FEATURES BY LAVA AND WATER

Volcanism has been the primary mechanism for the initial formation and modification of the crust on Mars for billions of years.Much of the planet's surface bears traces of volcanic activity to varying degrees.Volcanic activity has also played a key role in creating some of the largest features of the Martian landscape.For example, the Elysium and Tharsis regions are vast topographical uplifts [2, 5, 9] that dominate much of the surface of Mars.They were formed over several billion years by the accumulation of lava and other materials erupted from the planet's interior.Modern lava flows are the result of repeated outpourings of molten basaltic rock that occurred during non-explosive eruptions.In this case, the flows moved downward from the site of the eruption.Moving over the newly formed surface, each subsequent time such flows expanded, creating new side branches.Therefore, they were able to extend for many hundreds of kilometers.Usually eruptions occur at a temperature of lava material of 1400-1500 K. Inside such lava flows, so-called lava tubes are usually formed, which look like peculiar pipelines through which lava flows with a fairly low viscosity.When such a lava flow spreads from the source of the eruption from the volcanic vent, the material on its surface slowly cools and hardens; and under the hardened layer, the lava inside still remains quite hot.When the entire flow finally stops, the lava can only partially fill the space of the tube under the hardened layer, or it will drain completely down, leaving the tube empty.If the lava tube passes close enough to the surface, the roof can partially or completely collapse (Fig. 1, a).Moreover, the lines of the edges of such pits can repeat the course of the entire lava tube.Sometimes only a small part of the ceiling of the lava tube can collapse.In this case, only small openings similar to cave entrances or a "light window" will be visible on the surface (Fig. 1, b).Significant areas of the surface, and especially in the northern hemisphere of the planet, are covered with fairly smooth plains, which were formed during the outpouring of fairly fluid lava.The lava material on such plains filled older eruption craters and impact basins and depressions, leveling the overall relief [3,4,6,10,16].