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The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in 1998 confirmed that a vast region of Mars south of the Elysium volcanoes is covered by a relatively young lava surface that was very fluid when it erupted--so fluid that it ran more than a thousand kilometers (more than 600 miles) across a region known as the Elysium Basin and a channel named Marte Vallis. MOC image 38804 (above) shows a portion of Marte Vallis ( 7.1 N latitude and 182.7 W). When it was forming, the lava flowed from the lower left, toward the center right, then curved to the left and flowed toward the top-center of the frame. The center of the lava flow in image 38804 has a wide, shallow channel bounded by steep, discontinuous walls--also known as levees. Such leveed channels are commonly the conduit through which some of the later stages of molten rock are transported along a lava flow. The margins of the lava flow are broken into plates--some of them several kilometers across. These plates were once part of a hard, rock crust that floated on molten lava. As the lava flowed down Marte Vallis, huge chunks of this crust broke off at the margins of the flow and floated a few kilometers away from where they had originated. Long after the lava had cooled and hardened, a distant meteorite impact splashed ejecta across the martian surface such that a field of small craters--known as secondary craters--formed on top of the lava flow shown here. Researchers working with MOC data discovered that there were lava flows that could be even younger that this one in the Elysium reigon and Amazonis. Some of them display so few superimposed impact craters that they are believed to be contemporary, or even possibly current, leaving the possibility open that there is still some active volcanism on Mars.
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