Polar Wandering On Mars
Certain areas of Mars have eroded at a very low rate (less than a millimeter in a million years). Yet elsewhere at the same latitudes there are regions that have been heavily stripped and etched by the wind. Ancient networks of narrow valleys, once cut into the surface by flowing water and mud, suggest a warm climate, and yet such features are found within 10 degrees latitude of the southern polar ice cap. The polar ice caps, themselves, appear to be much younger than the other Martian surfaces. These paradoxes and many others can be resolved by one simple hypothesis, namely that the orientation in space of the Martian crust has shifted with respect to the planet's axis of spin. This "Polar Wandering" is caused by instabilities due to the redistribution of mass within the planet or on its surface. Possibly Olympus Mons' massive weight and Valles Mareneris' lack there of has caused this wandering. The image to the right shows what are believed to be polar deposits. Except these deposits were found near the equator. They beat a striking similarity to similar ones found at the poles.
The grazing impacts (left), the ages and locations of the layered equatorial deposits and the distribution of the features that seem to indicate polar or near-polar locations make it possible to trace the path the poles may have followed as they wandered across the Martian surface. They seem to not have wandered steadily but to have changed place in rapid spurts followed by long pauses. Keeping in mind that Mars' surface is believed to float as one surface because it has no plate tectonics perhaps several catastrophic events such as asteroids smashing into the surface caused the crust to shift.
The north pole's most recent stable position (before its present one) seems to have been at 160 degrees west longitude and 45 degrees north latitude, an area to the northwest of Olympus Mons. This orientation would place the south pole near the southwestern part of an enormous impact crater called the Hellas Impact Basin. It has been expressed that this impact crater may have been the cause of a mass planetary extinction, capable of changing a whole planet's environment.
About 2 to 3 billion years farther back in time, the North pole seems to have paused at 150 degrees west longitude and 5 degrees latitude, a location south of Olympus Mons near the Tharsis volcanoes. Dates based on comparisons of crater statistics indicate that the volcanoes may have begun their massive eruptions just before the pole shifted to the north. Such volcanic activity may well have contributed to the pole's shift to the later position northwest of Olympus Mons. Eventually, continued activity on the Tharisis region probably caused the pole to shift to its current position.