By David Rosenberg

Riyadh, Saudi Arabia

Saudi Arabia's Harrat Lunayyir lava field doesn't seem the kind of place that would generate much concern from anyone. Rocky where it isn't covered by sand, the area is bereft of vegetation and human habitation. Summer temperatures can exceed 100 degrees Fahrenheit. True, it is pockmarked with cones formed by eruptions, but those were formed quite a long time ago.

But, correctly or not, many Saudis worry about Harrat Lunayyir. Two years ago the area was shaken by a so-called swarm of more than 30,000 mini-earthquakes, which geologists say was caused by magma flows deep underground. The swarm left a 5-mile-long fissure and forced some 40,000 people to evacuate their homes.

The incident might have been forgotten, except that a Saudi news agency last week cited Professor Ali Adnan Eshky of King Abdulaziz University as warning of a "volcanic eruption" between the holy cities of Mekkah and Medinah sometime in the next two years. He based his forecast on U.S. and Saudi geological survey reports. That prompted a denial from the Saudi Geological Survey (SGS)

"The reports in the media appear to have misquoted or misinterpreted what has happened and are somewhat alarmist (which is not all that unusual)," Hani M. Zahran, director of the SGS's National Centre for Earthquakes and Volcanoes, told The Media Line. "At no time has SGS stated that an eruption is likely."

In fact, predicting earthquakes is a very inexact science, especially in the case of Saudi Arabia, which didn't begin monitoring seismic activity closely until the mid-1980s. That deprived geologists of the historical record they need to improve their understanding of the forces at work deep beneath the kingdom's surface.

Nevertheless, the 2009 incident made them more aware how much Saudi Arabia's west coast is vulnerable to tremors and volcanic activity.

The Saudi earth is better known for its bounties than its dangers. In the country's northeast, oil-soaked sedimentary rocks provide 20 percent of the world's proven petroleum reserves. In the west, there are few mineral resources but known earthquake hazards. While they present no danger to interrupting the world's oil supply, earthquakes and volcanic activity are a problem.

Not far from the Harrat Lunayyir lava field a much bigger one called Harrat Rahat exhibits many of the same characteristics and poses more risk to human life and property. At its southern end lie the key port of Jedda and Mekkah, Islam's holiest city. In the north lies Medinah, a city of about 1.4 million people, whose urban sprawl in recent years has encroached on the lava field itself.

The area has seen many eruptions over the past 20 million years, the source of which is underwater volcanic activity in the nearby Red Sea. The sea is the boundary between two tectonic plates, the Africa and Arabian and is a known source of earthquake hazard.

But, after studying the 2009 earthquake swarm in Harrat Lunayyir, geologists concluded that it was magma moving deep underground that caused the tremors. Where it came from - deep beneath the earth or flowing laterally from the Red Sea - is a matter of debate, but either way it set off a series of tremors between April and June of 2009, including one of 5.7 on the Richter scale.

When a similar event occurred in the year 1256, the magma forced its way out from under the ground near Medinah.

"The brilliant light of the volcano made the face of the country as bright as day; and the interior of the harim [the sacred area of the city] was as if the sun shone upon it," according to an account at the time. As the lava approached the city over a 50-day period, its inhabitants prayed at the Prophet Muhammad's tomb. The lava changed direction, saving the city.

In 2009, the molten rock never got closer than two kilometers from the surface. Nevertheless, it did establish what John Pallister, an American geologist who led a team that studied the swarm, calls a "pathway" for it to take the next time around. "That's the type of thing that tends to get reactivated," he told Nature News after publishing a detailed study of the event in the journal Nature Geosciences.

Eshky, who was quoted as warning that Harrat Lunayyir posed "dangers no less than a nuclear reactor," didn't respond to phone calls or e-mails from The Media Line.

Sigurjon Jonsson, an associate professor at King Abdullah University of Science and Technology and a co-author of the Nature Geosciences article, agrees that there is a "moderate sized" risk. But he doesn't think it is either imminent or poses a serious danger to Saudis.

"An eruption like in 1256 could occur again," he told The Media Line. "There's no reason to believe it is coming soon, but it didn't happen very long ago on the geological timescale. An eruption like the one in 1256 is fed from a magma intrusion like the one in 2009. The difference is that in 1256 it made it to the surface and started a volcanic eruption."

Earthquakes caused directly by the shifting of tectonic plates are a more serious risk in the kingdom's northwest. But in Harrat Lunayyir, even with the added volcanic danger, the worst case scenario won't lead to a Krakatoa: East of Jeddah kind of event, said Jonsson.

"They are more of a Hawaii-type of eruption. They typically do not emit of lot of ash or explode. They are lava flows that flow away from fissures that open," he said. "They don't pose an immediate danger to people. Unless the fissure opens right in the middle of a population center, people will have enough time to leave."


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