National Geographic : 1977 Jan
Gargantuan volcano.., plunging canyons Olympus Mons 15 miles high GIANT OLYMPUS MONS, its western flank wrapped in clouds (right), soars 15 miles above its plain. Along side it, earth's loftiest peaks (above) are mere foothills. The volcano's 45-mile wide caldera would extend from Baltimore to Washing ton, D. C., its 335-mile base from Montreal to New York City. How did it get so huge? According to Dr. Michael H. Carr of the Viking team, on Mars there appears to be no plate-tectonic activity the movement of great sec tions of planetary crust-as there is on earth. "Hence," he says, "the volcano could sit over the same plume of lava and grow forever and ever." Grand Canyon 18 miles wide, I mile deep AWESOME ABYSS: An 80 mile segment of Ius Chas ma (right) joins with other rifts to form Valles Marineris, the deepest canyons known in the solar system. As much as 150 miles wide and four miles deep, Valles Marineris would stretch across the continental United States. In comparison, the Grand Canyon of Arizona (above) is merely a ditch. Faulting createdtheseMar tian canyons; vast landslides and wind erosion enlarge them. Geologists believe that a series of episodes over a billion-year span shaped the canyon system. Despite such titanic geological events, Mars appears to be less active tectonically than the earth. No tremors jarred Viking's seismometer in the early weeks of monitoring.