CHAPTER 22 | COMPARATIVE PLANETOLOGY OF VENUS AND MARS 471
Remember that the colors in this image are artifi cial; if you
could walk across these lava fl ows and shine your spacesuit’s
white headlight on them, you would fi nd them solid, dark gray
stone. Sapas Mons and other nearby volcanoes are located along
a system of faults where rising magma evidently broke through
the crust.
In addition to the volcanoes, radar images reveal other
volcanic features on the surface of Venus. Lava channels are
common, and they appear similar to the sinuous rilles visible
on Earth’s moon. Th e longest channel on Venus is also the
longest known lava channel in the solar system. It stretches
6800 km (4200 mi), roughly twice the distance from Chicago
to Los Angeles. Th ese channels are 1 to 2 km wide and can
sometimes be traced back to collapsed areas where lava appears
to have drained from beneath the crust.
For further evidence of volcanism on Venus, you can look
at features called coronae, circular bulges up to 2100 km in
diameter containing volcanic peaks and lava fl ows. Th e cor-
onae appear to be caused by rising currents of molten magma
below the crust that create an uplifted dome and then withdraw
to allow the surface to subside and fracture. Coronae are some-
times accompanied by circular outpourings of viscous lava called
pancake domes, and by domes and hills pushed up by molten■ Figure 22-7
(a) Volcano Sapas Mons, lying along a major fracture zone, is
topped by two lava-fi lled calderas and fl anked by rough lava
fl ows. The orange color of this radar map mimics the orange
light that fi lters through the thick atmosphere. (NASA) (b) Seen
by light typical of Earth’s surface, Sapas Mons might look more
like this computer-generated landscape. Volcano Maat Mons
rises in the background. The vertical scale has been exagger-
ated by a factor of 15 to reveal the shape of the volcanoes and
lava fl ows. (Copyright © 1992, David P. Anderson, Southern Methodist
University)Radar map■ Figure 22-6
Impact crater Howe in the foreground of this Magellan radar image is 37 km
(23 mi) in diameter. Craters in the background are 47 km (29 mi) and 63 km
(39 mi) in diameter. This radar map has been digitally modifi ed to represent
the view as if from a spacecraft fl ying over the craters. (NASA)
Radar mapaRadar map100 kmbTh e radar image of Sapas Mons in ■ Figure 22-7 shows a
dramatic overhead view of this volcano, which is 400 km (250 mi)
in diameter at its base and 1.5 km (0.9 mi) high. Many bright,
young lava fl ows radiate outward, covering older, darker fl ows.