From http://www.jpl.nasa.gov/galileo/

   
                       Geologic Landforms on Io (Area 5)
                                       
   
   
   NOTE: This JPEG image is made available in order to share with the
   public the excitement of new discoveries being made via the NASA/JPL
   Galileo spacecraft. Galileo scientists are in the process of
   calibrating and validating this data. The full digital image necessary
   for scientific analysis will be released within one year of receipt of
   this orbit's last data.
   
   This image is available only on the WWW; it is not available in
   hardcopy or other forms.
   
   
     _________________________________________________________________
   
   
   
Geologic Landforms on Io (Area 5)

   
   
   Shown here is one of the topographic mapping images of Jupiter's moon
   Io (Latitude: -40 to +90 degrees, Longitude: 210-320 degrees) acquired
   by NASA's Galileo spacecraft, revealing a great variety of landforms.
   There are rugged mountains several miles high, layered materials
   forming plateaus, and many irregular depressions called volcanic
   calderas. There are also dark lava flows and bright deposits of SO2
   frost or other sulfurous materials, which have no discernable
   topographic relief at this scale. Several of the dark, flow-like
   features correspond to hot spots, and may be active lava flows. There
   are no landforms resembling impact craters, as the volcanism covers
   the surface with new deposits much more rapidly than the flux of
   comets and asteroids can create large impact craters. The volcano Ra
   Patera, seen to have an active plume 75 km high during Galileo's first
   orbit in June 1996, is located on the bright limb of this image but
   no plume can be seen, so it is now (5 months later) inactive.
   
   North is to the top of the picture and the sun illuminates the surface
   from the left. The image covers an area about 2800 kilometers wide and
   the smallest features that can be discerned are 4.1 kilometers in
   size. This image was taken on November 6th, 1996, at a range of
   403,100 kilometers by the Solid State Imaging (CCD) system on the
   Galileo Spacecraft.
   
   Launched in October 1989, Galileo entered orbit around Jupiter on
   December 7, 1995. The spacecraft's mission is to conduct detailed
   studies of the giant planet, its largest moons and the Jovian magnetic
   environment. The Jet Propulsion Laboratory, Pasadena, CA manages the
   mission for NASA's Office of Space Science, Washington, DC.
   
   This image and other images and data received from Galileo are posted
   on the World Wide Web, on the Galileo mission home page at URL
   http://www.jpl.nasa.gov/galileo.