Underground Volcanic Activity Unleashed Martian Floods, Geologists Say

Underground Volcanic Activity Unleashed Martian Floods, Geologists Say

January 20, 1999

(AP) -- Underground volcanic action on ancient Mars sculpted gorges far larger than the Grand Canyon and melted enough water to feed floods of biblical proportions, two geologists theorize.

Most scientists have attributed Mars' gorges to the bowing and stretching of the terrain from surface forces. Under the new theory, such features were instead shaped from below by rising wedges of molten rock known as dikes.

Under the new theory, the dikes also would have melted vast quantities of ice. This would explain the colossal floods that scientists generally believe scoured Mars 2 billion to 3 billion years ago.

The theory, which appears Thursday in the journal Nature, was devised by geologists Dan McKenzie and Francis Nimmo at the University of Cambridge in England.

Under their scenario, dikes pushed up to within several miles of the surface, forcing the rock above to jut upward and outward. The area in the middle sagged, forming a canyon.

Meanwhile, the molten rock melted ice in the frozen ground, underground pools formed and spread, and the rock above -- as if afloat -- shifted into the broken, chaotic pattern characteristic of Mars.

The water trapped underground could have offered the sort of warm, moist oases where some have suggested that life could have survived. When the water ultimately found its way to the surface, it collected in the canyons. The two geologists calculated that such a process could have let loose floods of 400 trillion gallons or more.

McKenzie argued that a gigantic dike larger than any on Earth, or a series of smaller ones, could run beneath the canyon network known as the Valles Marineris, the planet's best-known landmark.

The Valles Marineris stretches about 2,500 miles -- roughly the distance from New York to San Francisco -- and runs as deep as 6 miles. Its walls tower more than five times as high as those of the Grand Canyon.

Alfred McEwen, a geologist at the University of Arizona, challenged the molten dike theory as the explanation for Mars' canyons. He said there is scant evidence that there was full-scale volcanic activity, such as volcanoes or lava flow, at the time the gorges took shape.