Wednesday, July 13, 2011
A Trip to the Moon and a Trip to the Mantle (well, sort of...)
Today's discovery was on what I consider the real "loneliest highway in America", Highway 6 from Tonopah to Ely, Nevada. Not a single gas station or business for 170 miles. Along the way is a really interesting volcanic area, the Lunar Crater Volcanic Field, an area of 100 square miles or so of basaltic cinder cones and lava flows dating from the last million years or so, with the most recent activity in the last 20,000 years. Astronauts trained in the area during the Apollo missions.
About 7 miles off the highway about 75 miles east of Tonopah, Lunar Crater is a big hole, about 3,800 feet across and 430 feet deep. It is not a cinder cone or anything like one. It is a pit caused by the explosion of groundwater when magma came close to the surface. These craters are called maars. Similar features are seen at Death Valley (Ubehebe Crater), and at Mammoth (Inyo Craters).
The other interesting item of the day was an olivine crystal that came to the earth's surface from the deep mantle, via a lava flow near Lunar Crater. It's the biggest I've ever found (note the penny for scale). Chunks of mantle that are carried in lava like this are called xenoliths.