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| Maar on Harrat Shamah, northwest Saudi Arabia -- Hydrovolcanic eruptions associated with cylindrical intrusions of basaltic magma have generated numerous maars on the basalt volcanic field of Harrat Shamah. The maar shown here has a diameter of about 1 kilometer, which is typical of such hydrovolcanic craters on the harrat. Note the floor of the maar is excavated below the surface of the surrounding plateau, thus exposing underlying basement rocks. The ejecta blanket of composed of basalt fragments and phosphate-rich sediments are well exposed along the sides of the crater. Photo by Vic Camp. |