Courtesy of Geosciences Department These three-year old images were taken by the Mars Orbital Camera on the Mars Global Surveyor Spacecraft. They show geological evidence of catastrophic flooding.

How did the Tucson Mountains form? Inch by inch.

Over millions of years, the Earth's plates slid around at a rate of 2 inches a year, colliding and slowly pushing up land to form the range we see today.

Though much of Earth's topography was formed at this snail-like pace, some events were geologically instantaneous, energetic and often violent floods that drastically changed the surface of the planet. These are called "superfloods."

Unlike floods that result from heavy rainfall, like those during monsoon season, superfloods are sudden, rare and extremely powerful. They are usually associated with ice caps, not climate.

Victor Baker, a University of Arizona hydrology and geosciences professor, has been studying the phenomenon of superfloods, both on this planet and on Mars, for 35 years.

"It's basically a detective story," he said. "We look for clues and how they fit together. We're interested in not just the culprit but the whole context surrounding it."

While most of geology is a study of the present, analyzing the current topography and applying it to the past and future, the study of superfloods is all history.

"I'm the oddball because I study the past," Baker said. "And at 4.6 billion years old, the Earth has a lot of past."

Although the biggest superfloods occurred during Earth's ice age, which peaked about 20,000 years ago, these floods - also called catastrophic or cataclysmic floods - can still occur today.

One occurred in 1996 in Iceland, when an eruption under the glacier Vatnajškull released thousands of tons of water and ice.

Devon Burr, a UA geosciences doctoral candidate, studies Iceland as a "terrestrial analog" - or earthly example - of what flooding might have been like on Mars.

"We look for features that we think might be similar to features on Mars," she said. "Then, we can examine it close up and get more ideas about its geological significance, which we can then extrapolate to Mars."

Just like Iceland, Mars has a very volcanically active past and possibly is still volcanically active.

However, the superfloods on Earth tend to come out of glaciers, as did the one in Iceland in 1996. But on Mars, Burr said, the floods come out of fissures, deep cracks in the ground formed from volcanic eruptions.

"The mechanism of these floods is different, but the flow processes and the characteristics of the floods themselves are similar," she said.

"It has to do with our exploration of Mars," Burr said. "We're just trying to understand the water story there."

Robert Webb, a research hydrologist at the U.S. Geological Survey and an adjunct professor in the hydrology and geosciences departments, has studied large floods caused by rainfall and superfloods caused by glaciation events.

Trying to determine the Southwest's flood risk, Webb often looks to the past for information on the future, studying superfloods that occurred in the region more than 100,000 years ago.

"It's remarkable that we have found what we have already found" from floods that occurred so long ago, he said.

Though the largest floods can't be predicted, "understanding these floods is paramount to how we should estimate flood frequency," Webb said.

"The study of superfloods had a big unknown," Baker said. "You could not predict what you would find. And we have developed a whole science of looking at floods of the past. We embark upon a scientific investigation, and we don't know where it's going to go."