Perilous Times
30,000 earthquakes reawaken Ancient volcanic field in Saudi Arabia
In 2009, more than 30,000 earthquakes struck an ancient lava field,
opening up a five-mile long crevice. Sensors shoow that magma has risen
to roughly a mile below the surface of the Earth, and eruptions remain
possible.
The view of one of several volcanos in the area of Al-Aayiss near the
Saudi city Madina, west of the oil-rich kingdom. Several earthquakes
were registered in the area including one on May 20, 2009 with a
magnitude of 5,4,
By Charles Q. Choi, Our AmazingPlanet Contributor / September 26, 2010
A swarm of thousands of earthquakes that struck the corner of Saudi
Arabia nearest to Egypt in 2009 helped reveal that the area is
unexpectedly volcanically active, scientists now report.
The seismic readings that researchers managed to collect from these
quakes could help predict when volcanoes might erupt in the future,
investigators added.
Scientists had largely thought northwest Saudi Arabia was quiet,
geologically speaking. Few earthquakes and few volcanic eruptions have
been recorded there in the past millennium.
IN PICTURES: Volcanoes around the world
However, between April and June 2009, more than 30,000 earthquakes
struck an ancient lava field there named Harrat Lunayyir, with 19
earthquakes of magnitude 4 or greater striking at the swarm's peak on
May 19, including a magnitude 5.4 quake that fractured walls in the
town of Al Ays. Sensors even suggested that a volcanic eruption was
possible. Alarmed, the Saudi Arabian government then evacuated 40,000
people from the region.
Part of Red Sea Parting
The lava field of Harrat Lunayyir is part of a "lava province" roughly
70,000 square miles (180,000 square kilometers) in size that began
forming 30 million years ago when Arabia split from Africa, rifting
that helped create the Red Sea. Harrat Lunayyir was previously
considered inactive because of its location on the margins of the
continental rift, nearly 120 miles (200 kilometers) away from the
active center of spreading beneath the Red Sea.
Still, "the Red Sea rift is a very active place to start with, with a
chain of volcanoes down the middle of it that we're rarely aware of
because they are underwater," said researcher John Pallister, a
volcanologist and chief of the U.S. Geological Survey's volcano
disaster assistance program. "When continents are being pulled apart as
you have there, you'll often see intrusions of magma on the shoulders
of the rift."
The researchers discovered a roughly 2-mile-long (3-km-long) rupture
had opened up in the area and widened to 5 miles (8 km) long during the
most powerful quake. Satellite radar images suggested the most likely
cause of this fault was magma intruding upward over a 6-mile-long
(10-km-long) stretch.
Based on these findings, on June 19, 2009, the researchers forecast a
moderate chance of a volcanic eruption and a low probability of
magnitude 5 or greater earthquakes in the two months following. A
decline of seismic activity by August 2009 led the scientists to
conclude the crisis had ended, allowing evacuees to return to their
homes and daily lives.
Magma rises
Still, now that magma has risen to shallow levels roughly a mile (2
kilometers) below the surface of the Earth, eruptions remain possible,
and the authorities have to remain vigilant, the researchers said.
"It is more likely that we'll get additional intrusions of magma and
potentially even an eruption in this area — the pathway is prepared,"
Pallister told Our Amazing Planet.
The highly detailed readings the Saudi Geological Survey collected from
these quakes might be able to help scientists forecast volcanic
eruptions in the future, Pallister added.
Volcanic quakes often generate a mix of high- and low-frequency seismic
waves that could yield clues as to when an eruption might occur. These
signals are often dulled by the nature of the earth they pass through,
but when it came to the Arabian quakes, they were detected through the
crystalline rocks of the area quite clearly. The low-frequency seismic
waves detected during the quakes seemed to show magma flowing under the
earth, while the high-frequency waves indicated fracturing of
crystalline rocks as magma crept toward the surface.
"Understanding what these signals mean could prove instrumental to
forecasting what can be deadly events worldwide," Pallister said.
The scientists detailed their findings online Sept. 26 in the journal
Nature Geoscience.