Harrat Khaybar, a major volcanic field in Saudi Arabia, showcases a diverse range of volcanoes and eruptions, reflecting millions of years of geological activity. The contrasting colors of lava and ash reveal the geologic origins of Harrat Khaybar’s volcanic cones.
While the Arabian Peninsula is known for its vast deserts of sand, the area also contains extensive fields of lava. At least 12 volcanic fields, known as harrats, are contained in the western half of the peninsula. One such field is the 14,000-square-kilometer (5,400-square-mile) Harrat Khaybar, one of the largest in Saudi Arabia.
Geological Formation of Harrat Khaybar
Harrat Khaybar was formed by eruptions over the past 5 million years along a 100-kilometer (60-mile) vent system that runs north-south. According to the Smithsonian’s Global Volcanism Program, the volcanic field is still active, and eight lava flows are less than 1,500 years old. The last known eruption was reported in Harrat Khaybar in the 7th century.
Recent Volcanic Activity
Three of the youngest volcanic vents in Harrat Khaybar can be seen in this image, acquired by the OLI-2 (Operational Land Imager-2) on Landsat 9. These volcanoes resulted from different eruptive styles: Jabal Qidr is a stratovolcano (or composite cone); Jabal Abyad is a felsic dome; and Jabal Bayda is a tuff cone.
Unique Features of Jabal Qidr, Jabal Abyad, and Jabal Bayda
Jabal Qidr, in the northern part of the volcanic field, is built from several generations of dark, basaltic lava flows. Qidr has a 400-meter-diameter summit crater and exhibits the textbook cone shape of a stratovolcano. This is the only stratovolcano in the harrats of western Saudi Arabia.
Jabal Abyad, in the center of the image, was formed from a more viscous, silica-rich lava classified as rhyolite. While Jabal Qidr exhibits the cone shape of a stratovolcano, Jabal Abyad is a lava dome—a rounded mass of thicker, more solidified lava flows. Abyad’s dome reaches over 2,090 meters above sea level, the highest elevation amongst all the surrounding harrats.
To the west of Jabal Abyad is Jabal Bayda, a tuff cone volcano with a much larger summit crater measuring 1,400 meters in diameter. Tuff cones form from the interaction of rising magma with water. When heated rapidly by lava, water turns to steam and expands violently, fragmenting the lava into plumes of very fine grains of ash.
Volcanic Colors and Naming
Abyad and bayda are the masculine and feminine words for “white” in Arabic. The lighter color of these mountains comes from the ash of comenditic lavas that are rich with silica. The white and beige colors stand out against the darker basaltic lava of Qidr.
NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey.
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1 Comment
Being composed of basalt, I would expect Jabal Qidr to be a shield volcano such as is found in the Hawaiian Islands. Stratovolcanoes are more commonly composed of andesite, diorite, or other rocks varying in composition over time, which are intermediate in composition between mafic and acidic. It appears that the lighter-colored felsic (acidic) rocks overlie the dark basalts (mafic), making them younger. It is common for the composition of mafic magmas to become acidic over time. I don’t have personal experience with the rocks found in this harrat; however, I suspect that Ms. Cassidy is mistaken in her nomenclature.