he tight cluster of earthquakes was moderate compared with others in Yellowstone's past, including one in April 2004 in which more than 400 earthquakes were recorded over three days.

"It piques our curiosity, but it's not out of the range of normal behavior," Henry Heasler, Yellowstone's principal geologist, said of the Oct. 14 activities.

Park officials said the earthquakes were more likely caused by the underground movement of hot water and gas, rather than the migration of magma.

The largest swarm recorded in Yellowstone was in the fall of 1985 when about 1,800 earthquakes were registered, ranging in magnitude from 1 to 4.9. Around the same time, the huge Yellowstone caldera stopped slowly rising and began slowly falling.

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Yellowstone Volcano Observatory: http://volcanoes.usgs.gov/yvo/

There has been no word about any victims or damage.

According to forecasts made by Japan's Meteorological Agency, there is no tsunami (devastating oceanic wave) threat.

It struck at 11:03 a.m. (03:03 GMT) and was the most powerful of six quakes to hit the same region in the last two days.

Local officials said they had no immediate reports of damage or casualties on the remote, sparsely populated island.

Indonesia, the world's largest archipelago, is prone to seismic upheaval due to its location on the so-called Pacific "Ring of Fire," a string of volcanos and fault lines encircling the Pacific Basin.

Current thinking is that the Chicxulub meteor wiped out the final era of dinosaurs. But lead researcher Gerta Keller thinks that was only the beginning of Earth's spiral into chaos.

"The Chicxulub impact could not have caused the mass extinction," says Keller in a statement. "Because this impact predates the mass extinction and apparently didn't cause any extinction."

Researchers drilled at the Mexico crater location and removed marine sediments. These reveal the meteor hit Earth 300,000 years before the mass extinction in question, researchers say. Fossils found in the same area, at about the same age, seem to be undamaged by the impact.

After Chicxulub, a series of meteors assaulted Earth's surface over the next 300,000 years. At the same time, super-volcanoes in India erupted and released a massive amount of greenhouse gases into the air - rapidly raising Earth's temperature and putting life on the brink.

Finally, a massive meteor impact delivered the knock-out punch and drove the dinosaurs to extinction. The evidence it left behind in the fossil record is the anomalous spike in iridium, an alien material that was most likely delivered to Earth by meteor.

Keller will present her new theory at the Annual Meeting of the Geological Society of America in Philadelphia this week.

In the case of the Oracle at Delphi, the focus has been on the nature of the fumes that may have influenced the prophecies. For 10 centuries, successive Pythias issued their oracles to the thousands of pilgrims who made their way to Apollo's shrine at Delphi.

The Pythias were real enough, although their prophecies were often ambiguous. But could their trance-like states have had a basis in geological reality? Could there really have been a gas released from under Apollo's shrine that induced transcendental states in someone sitting on a tripod above a fissure in the ground?

An archaeological excavation early in the 20th century found no signs of a real chasm or fissure under the temple at Delphi, but studies over the past decade have revealed the presence of two geological faults that cross each other directly under the shrine.

Luigi Piccardi, a geologist at the Institute for Geosciences in Florence, says recent investigations have revealed that there could indeed have been a gas-exhaling chasm at the oracle site.

If this chasm existed, it has long since sealed itself, Piccardi says. "The oracle site is positioned directly across the surface trace of a seismic fault that could rupture during earthquakes, thus creating a fissure in the ground from which gases such as carbon dioxide, hydrogen sulphate or methane could originate," he says.

Other scientists found traces of ethylene, a central nervous system stimulant, in a nearby spring. Ethylene is known to induce euphoria when inhaled in large enough doses. Was this the source of the Pythias' mystical powers?

This is one of several myths analysed scientifically in a book, Geology and Myths, to be published early next year by the Geological Society of London. Co-edited by Piccardi and Bruce Masse of Los Alamos National Laboratory in New Mexico, it will be the first set of peer-reviewed scientific papers discussing the geological reality behind some myths and legends.

The volume is an attempt to give the field of geomythology a sound academic grounding, with the aim of providing "a panorama on the study of the geological foundation to human myths".

The details of a legend may also help scientists to learn something new about geology. Piccardi's investigation of one Italian legend has helped geologists to see something they had missed.

The story is the supposed apparition of the Archangel Michael at the sanctuary of Monte Sant'Angelo. The legend, traditionally dated AD493, talks of the ground shaking when Michael appeared. According to the story, God's heavenly guardian left behind "footprints" in the rocks.

Seismologists had not thought this part of Italy to be particularly active, but Piccardi found ample evidence of a major seismic event, including a fault scarp in the floor of the shrine to the apparition - the "footprint", perhaps.

Another ancient myth on the other side of the world has led to fresh insights into a previously unknown seismic risk. The Duwamish people, native Americans who live in the Seattle area of the north- western United States and Canada, have a spirit with the body of serpent and the forelegs and antlers of a deer - an a'yahos. Old folk tell children not to look in the direction of an a'ya-hos because it could shake the ground or turn you to stone. Distinctive boulders and other stone markers at sites around the Seattle area are said to be haunted by a'yahos spirits.

Normally such superstition would not interest scientists, but that changed when images and excavations from a geophysical survey in the early 1990s revealed a hidden fault crossing Seattle and Puget Sound. Studies showed that the fault generated a powerful earthquake 1,100 years ago. But what was really intriguing was the discovery that many of the a'yahos stones were sited either on the fault line itself or at sites where there had been a major landslide.

Ruth Ludwin, a seismologist at the University of Washington, Seattle, published the findings in the journal Seismological Research Letters. She points out that there are dozens of native stories about great waves carrying away coastal villages in this region, often told as tales of mythical battles between thunderbirds and whales. But the reality behind the myth may lie in the actual occurrence of mega-tsunamis generated by undersea earthquakes.

Patrick Nunn, a geoscientist at the University of South Pacific in Suva, Fiji, is one of the growing band of geologists who believe that analysis of some myths may lead to new scientific discoveries. He points to the legend of the people on the island of Kadavu, in Fiji. The inhabitants have a story of a mountain that comes out of the sea - a description, perhaps, of a seabed volcanic eruption.

Nunn investigated the island's volcano in 1998. He first concluded that it had not erupted for 50,000 years, long before the island was first inhabited in about 2000BC. The legend, he believed, must have been imported from another Pacific volcanic region.

Months later, however, excavations for a new road revealed ancient pieces of pottery buried under a metre-deep layer of volcanic ash. Evidently, there had been a big eruption since the island became inhabited. The legend may easily have been homegrown - and taking it more seriously may have provided a vital clue to the island's recent volcanism. "The myth was right, and we were wrong," Nunn says.

The reality behind the folklore

Homer's description of Ithaca, the home of Odysseus in the Odyssey, baffles scholars. It bears little resemblance to the modern Greek island of Ithaki. Some geologists now believe that Ithaca is in fact Paliki, the western peninsula of Kefalonia, which may have been separated by a sea channel that was filled in more than 2,000 years ago. Geologists are testing to see whether Paliki could have been a proper island in the recent past, and so meet all the descriptions laid down in the Odyssey.

There are many legends in West Africa about haunted lakes that rise, sink or blow up despite there being no active volcanism in the region. Some scientists believe the tales may originate from real events similar to that which occurred in 1986 at Lake Nyos in Cameroon ( above). Carbon dioxide bubbling from deep rocks built up in the water over decades before it was released suddenly as a massive eruption that suffocated anyone living near by on lower ground; carbon dioxide is heavier than air and sinks. This could explain local taboos about living close to lakes or on the lower slopes of a mountain.

The biblical flood may have a basis in a real flood that occurred when rising sea levels in the Mediterranean after the last Ice Age topped the Bosporus Strait and poured into the lowlands of what is now the Black Sea. Walter Pitman and William Ryan of Columbia University amassed evidence that the Black Sea may have been created by just such a cataclysmic event that led to the flooding of many towns and villages over a vast area - giving rise to the legend of a vast deluge.