The face of Venus, Earth's hellish sister planet, is unexpectedly alive with cataclysmic change, according to geologists' interpretation yesterday of dramatic new images of the planet provided by the robotic Magellan spacecraft.

Towering mountain ranges are thrusting up and collapsing. Sinuous rivers of volcanic lava have flowed 200 miles. Meteors have blasted the deepest known crater in the solar system -- twice as deep as the Grand Canyon.

Other craters are big enough to hold the entire Beltway on the bottom. And some mysterious force has created a region of fractures and faults, intersecting with graph-paper uniformity unlike anything seen before.

Close-ups of the cloud-veiled planet nearest Earth were made public at a briefing by delighted members of the Magellan science team. Their spacecraft, whose work was delayed by technical problems, began mapping the surface using advanced radar on Sept. 15.

Magellan "is giving us a revolutionary new view of Venus," said planetary geologist James Head of Brown University.

The four new photographs released included a giant mosaic of Magellan images that revealed startling variety within an area the size of Wyoming.

The mosaic revealed a region scientists dubbed the Crater Farm, featuring three large meteorite-impact craters ranging 23 to 30 miles in diameter, in a fractured volcanic landscape.

In the past, students of Venus have observed it myopically, through the obscuring veil of its hot, toxic atmosphere, a lethal mixture of carbon dioxide and sulfuric acid clouds.

Some 20 probes from Earth have visited Venus since 1961, but Magellan's advanced radar is yielding such startling detail compared with its predecessors that it is like having "a microscope on Venus," Head said.

He noted that the craft, which shows details as small as 400 feet across, has mapped only 1.5 percent of the surface so far on its mission, which is to last at least 243 Earth days, or one Venusian day.

Scientists have been hungry for these close-ups because they believe Venus holds answers to questions about how planets change and, perhaps, what fate awaits Earth. The sizzling climate -- Venus's surface temperature is almost 900 degrees Fahrenheit -- is the result of a runaway greenhouse effect caused by the abundance of carbon dioxide in its atmosphere, a severe version of the conditions scientists fear humans may be creating on Earth.

Until now it had not been clear whether the face of Venus had long ago hardened into a death mask resembling the geologically lifeless surfaces of Mars, Mercury and Earth's moon, or that it has a constantly changing countenance like that of Earth, freshened by flows of molten rock from its depths and resculptured by erosion.

"I think Venus is very much alive in the broad sense," Head said. Although Magellan is not designed specifically to detect it, he added, "There is an excellent possibility there is active vulcanism {volcanoes} somewhere on the planet."

Earth is "water damaged," the historic record on its surface constantly rewritten by erosion. But Venus offers what scientists called "double and triple exposures" of its history visible on its surface.

Among the other features revealed yesterday:

Evidence that Venus's dense atmosphere destroyed smaller meteorites, allowing only the largest, some possibly flattened by atmospheric resistance into the shape of pancakes, to strike the surface. The object that blasted out the huge Meteor Crater in Arizona, for example, would never have made it through the Venusian atmosphere.

A region of criss-crossing faults that meet almost at right angles, covering an area equal to the state of Rhode Island. "This is really something we've never seen before," Head said.