The western half of the Arabian Peninsula contains not only large expanses of sand and gravel, but extensive lava fields known as haraat (harrat for a named field). One such field is the 14,000-square-kilometer Harrat Khaybar, located approximately 137 kilometers to the northeast of the city of Al Madinah (Medina). The volcanic field was formed by eruptions along a 100-kilometer, north-south vent system over the past 5 million years. The most recent recorded eruption took place between 600–700 AD.
Harrat Khaybar contains a wide range of volcanic rock types and spectacular landforms, several of which are represented in this astronaut photograph. Jabal (“mountain” in Arabic) al Qidr is built from several generations of dark, fluid basalt lava flows. Jabal Abyad, in the center of the image, was formed from a more viscous, silica-rich lava classified as a rhyolite. While the 322-meter high Jabal al Qidr exhibits the textbook cone shape of a stratovolcano, Jabal Abyad is a lava dome—a rounded mass of thicker, more solidified lava flows. To the west (image top center) is the impressive Jabal Bayda’. This symmetric structure is a tuff cone, formed by eruption of lava in the presence of water. The combination produces wet, sticky pyroclastic deposits that can build a steep cone structure, particularly if the deposits consolidate quickly.
White deposits visible in the crater of Jabal Bayda’ and two other locations to the south are sand and silt that accumulate in shallow, protected depressions. The tuff cones in the Harrat Khaybar suggest that the local climate was much wetter during some periods of volcanic activity. Today, however, the regional climate is hyperarid—little to no yearly precipitation—leading to an almost total lack of vegetation.