Victor Baker, a University of Arizona geologist and flood expert who was not involved in Tanaka's research, has been studying superfloods on Earth and Mars for years. Baker said the new study provides one more piece of the complex puzzle left by these catastrophic events, and the overall investigation will help scientists figure out how and why they occurred on both planets.

On Earth, superfloods are thought to have resulted when giant ice dams burst, particularly at the fringes of glacial ice. But volcanic eruptions on Earth may also have created superfloods similar to what Tanaka describes for Mars. Additionally, research that has yet to be published points to the possibility that Mars may have experienced ice-dam floods similar to those on Earth, Baker said.

Destruction from these events would not be countywide or even statewide in scope, but continental, Baker maintains. In past events on Earth, runoff altered ocean currents and changed the global climate, he said. Mars' climate may also have been altered throughout history by huge floods.

"The Mississippi River flood of 1993 was an extremely large flood for the upper part of the river," he began. The flood sent 30,000 cubic meters of water per second gurgling into the Gulf of Mexico. In the world's oceans, distinct currents each transport millions of cubic meters of water per second, he explained, typically 30 times more than the '93 flood. The flow of the Gulf Stream, along the Atlantic Seaboard, is even greater, shuttling 1,000 times more water per second than the Mississippi's best effort.

"Catastrophic floods discharge on the order of ocean currents," Baker finally said.

Yet that's not the worst of it. A superflood comes in a sudden burst. While ocean currents and even overflowing rivers move at speeds measured in feet or meters per second, superfloods rage at dozens of feet (or tens of meters) per second.

"The energy expenditure in catastrophic floods is immense," Baker said. He likened the effect to the difference between years and years of normal erosion versus the impact of an asteroid, which changes the landscape in an instant.

Because evidence of catastrophic flooding on Mars remains for billions of years, Baker said studying the Red Planet can fill gaps in knowledge about terrestrial superfloods, though the exact processes and mechanisms are not necessarily identical.

"We can see the evidence of these floods from very ancient times," he said. "Mars gives us something to study ... that we don't have on Earth."

Likewise, present-day Iceland, where volcanoes stew under sheets of glacial ice, is almost a mini- laboratory for studying what might have happened long ago on Mars. Eruptions melt the ice, and subglacial lakes form. Eventually enough water builds up that it bursts out. Iceland experiences huge floods every few years, Tanaka said.

Not exactly classic superfloods, these Icelandic events, but they are considered serious enough that the nation's highways and byways are dotted with alert stations to warn of impending torrents.