How Volcanoes Work

 Image Described in Caption
 Jabal Abyad, Saudi Arabia -- Two lava domes are exposed in this photo of the high central vent system of remote Harrat Khaybar, a large basalt plateau in western Saudi Arabia. The light-colored dome in the right background is composed of a felsic rock called comendite. Its name, Jabal Abyad, means white mountain. The lower portion of Jabal Abyad contains a previously unknown site of obsidian used to make Paleolithic tools. The dome in the foreground is composed of a more mafic rock type, called hawaiite. The flanks of the hawaiite dome are marked by neolithic stone walls. The basaltic lava in the foreground flowed over these stone monuments, indicating that the flow is younger than the neolithic walls. Photo by Vic Camp.