Before, during, and after avalanches on Mars

NASA / JPL / U. Arizona

Active avalanches on Mars

On February 19, 2008, while monitoring the edge of Mars' north polar cap for changes as the spring thaw arrives, Mars Reconnaissance Orbiter was fortunate to catch several avalanches in the act of spilling down the steep slope at the edge of the cap. Two avalanches are visible in this image, one large one near the top and a smaller one near the bottom. The cap is to the left; its steep cliff, running across the center of the image from top to bottom, is approximately 700 meters tall and reaches slopes as steep as 60 degrees. The steep part of the cliff is composed of layered material (the layers are difficult to see in this image) made mostly of water ice with atmospheric dust mixed in. To the right of the image, the cliff flattens out into a still moderate slope of about 20 degrees; this part of the cliff probably has a higher proportion of sand and dust in layers interspersed with ice-rich layers. The avalanches kicked up billowing clouds of dust that rise high into the air, casting shadows to their lower left.

NASA / JPL / U. Arizona / animation by Emily Lakdawalla

Before, during, and after avalanches on Mars

This animation flips back and forth between two images captured two weeks apart of the edge of Mars' northern polar cap by the HiRISE camera on Mars Reconnaissance Orbiter. Active avalanches -- or their immediate aftermath, visible as billowing clouds of dust -- are actually visible in both images. The image is about 500 meters wide. The shift in surface features between the two images is because Mars Reconnaissance Orbiter had to look off to one side of its orbital position in order to image the same area twice. The cliff is more foreshortened in the February 3 image than in the February 19 image.