Historic volcanic activity around Al Madinah
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The areas of Tertiary volcanism in western Saudi Arabia appear to be largely inactive at present. However, the Cenozoic volcanic lava field of Harrat Rahat, which is about 310 km long and lies between Makkah and Al Madinah, has experienced volcanism in historic times.The total volume of lava in this harrat is about 2000 km3, and volcanism
commenced about 10 million years ago, with the more recent flows toward the northern end of the harrat.
The oldest lavas near Madinah are geologically very young, only about 2 million years old. In this area the youngest “Post-Neolithic” lavas (less than 6000 years old) resulted from 11 eruptions, with 2 historic eruptions in AD 641 and AD 1256. The 641 AD eruption resulted in a small line of cinder cones to the southwest of the city. The last well-documented eruption in Saudi Arabia occurred in the northern end of Harrat Rahat near Al Madinah in 1256 AD/ 654 AH, and was preceded by significant earthquake activity for several days. Fountains of basalt lava were then seen 19 km to the southeast of the city, and lava advanced toward the city. The eruption continued for 52 days, and the lava flow reached to within 12 km of the city before activity ceased. About half a cubic kilometer of alkali olivine basalt was extruded from a 2.25 km-long fissure during this eruption. Three large scoria cones and three low spatter cones were produced at the vent zone, and the lava flowed a maximum distance of 23 km. The area continues to be of some concern, especially since the city is now expanding into the area of the flow, and SGS maintains a local seismograph network around this end of the harrat and the city to warn of any impending risk from an eruption, although there is a very low probability of this happening.
NASA World Wind Geocover2000 false color image of northern Harrat Rahat, derived from 2 infrared and 1 visible green spectral bands. The city of Al Madinah occupies the left side of the image, and the harrat lava flows are the black regions, with the most recent flows showing as the darkest areas. The volcanic cones or eruption centers are red/orange in this image. It can be seen that the flows from the 1256 AD eruption reached almost to the city, and are close to the present airport, part of which can be seen near the top edge of the image. Note that development is now taking place within the area of this historic lava flow, which increases the risk in the very unlikely event of any further volcanic activity in the area.