February 3, 1999

Recent Lava Flows on Mars

1. The Elysium Basin on Mars as viewed by NASA's Viking Orbiter 1 in 1978. Geologic features in the white box are shown in figure 2. For an image of Mars showing where the Elysium Basin is located relative to other Martian features, click here.

2. Enlarged Viking view of the white box of image 1.

3. Enlarged view of area identified as 21905 in images 1 and 2, as seen by NASA's Mars Global Surveyor in April 1998.

Click on images for enlarged views and more detailed descriptions.

Image Credits: Jet Propulsion Laboratory (JPL) and NASA (images 1 and 2). Malin Space Science Systems (image 3).

The close-up images of the Elysium Basin sent back to Earth by NASA's Mars Global Surveyor suggest repeated episodes of lava flows less than 250 million years ago or, more likely, less than 100 million years ago. This is rather recent by geological standards. If this interpretation is correct, these flows represent the youngest known, large-scale volcanic activities on Mars.

During each episode of volcanic outbursts, the lava followed the shallow gradients of the Elysium Basin toward lower elevations, spread out across the landscape, and formed temporary lava ponds in local depressions. The lava of one episode hardened well before the occurrence of the next episode; and, almost certainly, there are today lava beds on top of lava beds. Gradually, the lava flows leveled the original, much more rugged, topography.

Figure 2 shows the extreme flatness of the Elysium Basin landscape, which is interrupted only by occasional ridges a few dozen feet in height and some sparsely scattered impact craters. The Sun shines from the right in this image, casting dark shadows at the steeper ridge slopes and crater rims.

The strongest evidence for repeated volcanism and lava flows in the Elysium Basin is the pattern of the gray fragments and the bright cracks between them seen in images 2 and 3. These features are thought to have formed when the surface layers of molten lava flows cooled and hardened into solid crusts. The still-moving molten lava underneath broke up the crust into fragments, some miles across, and opened cracks between them. Eventually, as a volcanic episode ended, the entire lava stream cooled and hardened down to the bedrock.

This process of repeated lava flows and the formation of crusted fragments separated by cracks, which probably went on for millions of years, created the landscape seen today. The brightness variations between the fragments and cracks are probably due to differences in surface roughness and the degree to which windblown dust and sand have settled on their surfaces.

Interestingly, the number of impact craters in the Elysium Basin is much lower than in some other areas of Mars, such as in the planet's southern highlands. This is additional evidence that the floor of the Elysium Basin has been resurfaced in relatively recent times, most likely by lava flows as we discussed, wiping out craters from earlier times.

More Cool Stuff

For more information on NASA's Mars missions and images of Mars, go to:

http://mars.jpl.nasa.gov/
http://nssdc.gsfc.nasa.gov/planetary/marsurv.html

We obtained the global map of Mars at a site of the Planetary Data System (PDS) and US Geological Survey (USGS). By clicking anywhere on the map at the PDS/USGS site, you obtain an enlarged Viking view of the clicked area with the option of zooming in and out:

http://www-pdsimage.wr.usgs.gov/PDS/public/mapmaker/mapmkr.htm

The Planetary Data System (PDS), which is sponsored by NASA's Office of Space Science, archives and distributes digital data from past and present NASA planetary missions, astronomical observations, and laboratory measurements. The site offers authoritative information and many useful links for both the professional and amateur astronomer:

http://pds.jpl.nasa.gov/pds_home.html

We have featured Mars regularly on our Observatorium site. Our most recent Mars articles are:

"Ancient Hydrothermal Activity on Mars," November 18, 1998
http://observe.ivv.nasa.gov/nasa/ootw/1998/ootw_981118/ob981118.html

"Mars Global Surveyor Arrived at the Red Planet," September 3, 1997
http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_970903/ob970903.html

"Mystic Mars"
http://observe.ivv.nasa.gov/nasa/mars/mystic_mars.html

As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the space sciences:

The University of Washington has developed and disseminates educational materials based on real-time and retrospective atmospheric science and space sciences data with "Live From Earth & Mars."

http://www-k12.atmos.washington.edu/k12/

Windows to the Universe is a site created by the University of Michigan that offers access to information about Mars and the other planets of the solar system.

http://www.windows.umich.edu/

Other LTP sites that are dedicated to space science can be found at:

http://learn.ivv.nasa.gov/education/topics/space_sci.html