![]() ![]() When this magma surfaces along the fault, the crust above the chamber collapses, forming the patera.” Hi’iaka Montes. “When the stress environment changes,” McKinnon said, “a magma chamber can form at midlevel in the crust. The model might also explain why the mountains are associated with shallow, irregular depressions called patera. “When these faults breach the surface, those forces are released, and the entire stress environment around the fault changes, providing a pathway for magma to erupt.” “The compressive forces deep in the crust are incredibly high,” Mckinnon said. It might explain, for example, why there are often recent eruptions near mountains. “It’s a neat demonstration of how things might actually work,” McKinnon said. When it breaches the surface, it actually overshoots, forming a scarp, or cliff, and stretching the surface of the overhanging block. The simulations show that the strain localizes to a single fracture, or fault, that starts deep in the lithosphere and rips through the rock all the way to the surface. The stair-stepping is an artifact the simulation divides the crust into small elements so that simpler (solvable) functions can be used to describe the rock mechanics. The fault also provides a conduit for rising magma and collapsing magma chambers form “patera,” or depressions on the surface. As it breaches the surface, it pulls on the overhanging crustal block (to the left of the fault), and “extensional” features such as trenches called graben form there. A thrust fault rips to the surface of a numerical Io. We thought we could mimic this by beveling in the edges of a box, squeezing it as you might an accordion. “People have been squeezing planetary interiors forever to see what happens,” McKinnon said, “but we’re applying the squeeze differently, because on Io compression increases with depth the surface is not in compression. The numerical experiment described in Nature Geoscience tests this hypothesis through simulation. McKinnon and his former student, Paul Schenk, now at the Lunar and Planetary Institute in Houston, wrote a paper explaining this hypothesis in 2001. “All that lava spewed on the surfaces pushes downward and, as it descends, there’s a space problem because Io is a sphere, so you end up with compressive forces that increase with depth.” “The planetary community has thought for a while that Io’s mountains might be a function of the fact that it is continuously erupting lava over the entire sphere,” McKinnon said. Bland, a research space scientist at the USGS Astrogeology Science Center in Flagstaff, Ariz., publish a computer model that is able to make numerical mountains that look much like the jutting rock slabs on Io. ![]() In the May 16 online advance issue of Nature Geoscience, McKinnon and Michael T. Since Io buries the evidence of its tectonic processes under a continually refreshed coating of lava (adding 5 inches a decade), the scientists have turned increasingly to computer simulations to solve the problem. By what process consistent with everything that is known about Io could these bizarre mountains have formed? Louis, the mountains of Io are an intriguing puzzle. From space, they look rather like the blocky chips in the fancier kind of chocolate chip cookie.įor planetary geophysicists like William McKinnon, professor of earth and planetary science in Arts & Sciences at Washington University in St. ![]() ![]() While we favor majestic ranges stretching from horizon to horizon, the mountains on Io are isolated peaks of great height that jut up out of nowhere. They also don’t look like mountains on our home world. There are about 100 of them, and they don’t look anything like the low lying volcanoes. Io has no identified impact craters because massive volcanic eruptions continually resurface it. True color image of Jupiter’s moon Io made by the Galileo spacecraft. But once you absorb the fact that the moon is slathered in sulfurous lava erupted from 400 active volcanoes, you might turn your attention to scattered bumps and lumps that turn out, on closer inspection, to be Io’s version of mountains. Mountains aren’t the first thing that hit you when you look at images of Jupiter’s innermost moon, Io. ![]()
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