Saudi Eruption that Never was
Tuesday, September 28, 2010 2:26:23 PM
Both geobloggers have of course duly commented the new findings here and here, which makes my job easy - just read their blogs, and you are up to date, that is what I highly recommend.
Nevertheless just briefly this:
In 2009 (between April and June), more than 30,000 earthquakes struck an ancient lava field in Saudi Arabia - the extensive Harrat Lunayyir lava province formed during the past 30 million years in response to Red Sea rifting and mantle upwelling. The area was so far regarded as seismically quiet.
The Red Sea rifting pushed the African and Arabian tectonic plates apart, and the rifting is still going on, so that within many million years the two continents will have a large oceans between them.
Here is a Google situation map:
Location of Harrat Lunayyir: Latitude: 25.17°N * Longitude: 37.75°E (if the map shouldn’t turn up!)
The authors used geologic, geodetic and seismic data to show that the earthquake swarm resulted from magmatic dyke intrusion. They documented a surface fault rupture that is 8 km long with 91 cm of offset. This deformation is best modelled by the shallow intrusion of a north-west trending dyke that is about 10 km long. Sensors show that magma has risen to roughly 2 km below the surface of the Earth, and eruptions remain possible. Rather than extension being accommodated entirely by the central Red Sea rift axis, the authors suggest that the broad deformation observed in Harrat Lunayyir indicates that rift margins can remain as active sites of extension throughout rifting. Their analyses allowed them to forecast the likelihood of a future eruption or large earthquake in the region.
The lava field of Harrat Lunayyir is part of a "lava province" roughly 180,000 square kilometres in size. Harrat Lunayyir is a basaltic volcanic field east of the Red Sea port of Umm Lajj. It contains about 50 volcanic cones. The hazard from these volcanoes is low, given the remoteness of the site and the type of eruption expected. Volcanic eruptions in Saudi Arabia are rare and only occur every few hundred years. According to contemporary accounts, the best known volcanic event in the region occurred in 1256, which sent flows of lava "like a red-blue boiling river" for 52 days into the holy city of Medina.