Subsurface volcanic activity and more than 30,000 earthquakes struck northwest Saudi Arabia in May 2009, according to a study published online this week in Nature Geoscience. The margins of continents that neighbour active oceanic spreading centres were previously considered to be seismically and volcanically inactive. But this finding indicates that the region is at risk from significant geohazards.

John Pallister and colleagues used field, satellite and seismic data to monitor the seismic activity observed in an ancient lava field, Harrat Lunayyir, in Saudi Arabia. During the volcano crisis, the ground surface ruptured into an 8-km-long fault, while magma was emplaced beneath the surface. Harrat Lunayyir was previously thought to be inactive because it is located on the continental margin, almost 200 km away from the active oceanic spreading centre beneath the Red Sea.

The unexpected volcano and earthquake crisis resulted in the evacuation of 40,000 people from the region and calls for the re-evaluation of our understanding of continental rift margins.