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Unlike most deep-sea basalt lavas, the rhyolitic lavas on the Alarcon Rise were very thick and pasty, like chunky peanut butter. As they emerged from the underwater volcano, they formed large, angular blocks, some of which tumbled down the sides of the volcano, eventually covering the sides of the dome in talus.
San Francisco - Scientists have discovered one of the world's weirdest volcanoes on the seafloor near the tip of Baja, Mexico.
The petite dome - about 165 feet tall (50 meters) and 4,000 feet long by 1,640 feet wide (1,200 m by 500 m) - lies along the Alarcón Rise, a
seafloor-spreading center. Tectonic forces are tearing the Earth's crust apart at the spreading center, creating a long rift where magma oozes toward the surface, cools and forms new ocean crust.
Circling the planet like baseball seams, seafloor-spreading centers (also called
midocean ridges) produce copious amounts of basalt, a low-silica content lava rock that makes up the ocean crust. (Silica, or silicon dioxide, is the main component of quartz, one of the most common minerals on Earth.)
But samples from the newly discovered volcano are strangely rhyolite lava, and have the highest silica content (up to 77 percent) of any rocks collected from a midocean ridge, said Brian Dreyer, a geochemist at the University of California, Santa Cruz. The results were presented last week at the annual meeting of the American Geophysical Union.
