Curious gaps in clouds may provide early warning of an earthquake, scientists believe.

Researchers spotted unusual cloud formations above an active fault in Iran before two large earthquakes struck the region.

It appeared to be more than coincidence, and now scientists are investigating whether clouds can predict major quakes.

Two geophysicists in China noticed a peculiar gap in the clouds covering southern Iran in satellite images from December 2004.

The gap stretched for hundreds of kilometres, and precisely matched the position of a main fault line. It was visible for several hours and remained in the same place, even though the surrounding clouds were moving.

At the same time, thermal images of the ground showed that the temperature had risen along the fault.

Sixty-nine days later, on February 22 2005, a 6.4 magnitude earthquake hit the area killing more than 600 people.

In December 2005 the phenomenon was seen again at the same location, a gap once again appearing in the clouds for a few hours. Sixty-four days later a magnitude six earthquake shook the region, New Scientist magazine reported.
The scientists, Guangmeng Guo and Bin Wang, suggested that an eruption of hot gases from within the fault may have caused water in the clouds to evaporate.
They believe if recognisable cloud formations precede large quakes they could be used as an early warning system.

Other experts are sceptical. Dr Mike Blanpied, from the US Geological Survey's Earthquake Hazards Program told New Scientist: "There is no physical model that explains why something would suddenly occur two months before an earthquake, and then shut off and not occur again."