Dunes and Dust in Arabia Terra

The battered region of Arabia Terra is among the oldest terrain on Mars. A dense patchwork of craters from countless impacts testifies to the landscape's ancient age, dating back billions of years.

In eastern Arabia lies an anonymous crater, 120 kilometers (75 miles) across. The floor of this crater contains a large exposure of rocky material, a field of dark sand dunes, and numerous patches of finer-grain material, probably dust. The shape of the dunes hints that prevailing winds have come from different directions over the years.

This false-color image, made from frames taken by the Thermal Emission Imaging System (THEMIS) aboard NASA's Mars Odyssey orbiter, shows the center of the crater's floor. The image combines a daytime view at visible wavelengths with a nighttime view at infrared (heat-sensing) wavelengths, thus giving scientists clues to the physical nature of the surface.

Fine-grain materials, such as dust and the smallest sand particles, heat up quickly by day and cool off equally quickly at night. However, coarser materials - bigger sand particles, gravel, and rocks - respond more slowly to the same daily cycle.

This means that when THEMIS views these late in the martian night, they appear warmer than the pools and patches of dust. In the image here, areas that are cold at night appear in blue tints, while the warmer areas show in yellows, oranges, and reds.

Location: 26.7N, 63.0E Released: 2006/02/07 Instrument: VIS Image Size: 37.7x34.2 km, 23.4x21.3mi, 2092x1907 pixels Resolution: 18m (59ft.)

Eruption of Augustine Volcano, Alaska

The Augustine Volcano was continuing to erupt, spewing ash, steam, and gases high into the atmosphere, when this image was acquired on January 30, 2006. The eruption began on Friday, January 27.

The volcano is located on an uninhabited island (of the same name, Augustine), located at roughly the center of the image; the plume that its eruption caused begins in the center of the image and trails towards the upper right corner.

This volcano is very active, and combined with its proximity to Anchorage, is one of the more serious natural hazards in the state of Alaska. Ash poses a health risk as well as a danger to navigation, hence the closure of local airports earlier in the week.

Previous major eruptions of the Augustine Volcano occurred in 1976 and 1986; the latter eruption blew ash into the air upwards of 14.5 kilometers (9 miles). The series of islands for which Alaska is famous is a part of an island arc, a string of volcanoes that form above what geologists call a "hot spot". The plate (on which the islands currently rest) moved over a column of hot magma or liquid rock and the islands were formed as the magma cooled into volcanic rock.

Augustine is a "stratovolcano", a large, conical mountain formed from lava flow and volcanic ash. Just under half of all volcanic eruptions in the last 10,000 years have been from stratovolcanoes -- including Mt. St. Helens in 1980 and 2004-2005.

Credit: Jeff Schmaltz; MODIS team; NASA

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