A One-Day Field Excursion to Northern Harrat Rahat

SGS-DF-2004-8 M. John Roobol
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ABSTRACT

As a contribution to the growing awareness of geohazard problems within Saudi Arabia, a one-day field excursion onto northern Harrat Rahat is described. The Toyota Landcruiser trip commences and finishes at Madinah International Airport, with a total driving distance of 103 km. The cars will cross the flanks of Harrat Rahat into the central vent zone. The 1256 A.D./654 A.H. lava flow and its vent zone will be visited, and the historic accounts discussed. A late prehistoric 11-km-long fissure system with vents will be visited next. Open fissures trending parallel to the vent zones and up to 1.4 km long, 100 cm wide, and open to a depth of 21 m, will be visited and their seismic implications discussed. Within the central vent zone, the trachyte dome complex of Jabal Matan will be visited. Finally, the permanent geohazard camp of the SGS will be visited and the operation of the telemetered microseismic network around the city of Al Madinah inspected. The operating seismographs can be seen recording local microseismic activity as well as regional events. A discussion of the volcanoseismic problems of the area will follow, including the problem of distinguishing shallow tectonic events from city noises.

 

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Roobol, M.J., 2004, A one-day field excursion to northern Harrat Rahat: Saudi Geological Survey Data-File Report SGS-DF-2004-8, 15 p., 6 figs., 5 maps.