Introduction to Planetary Science

188 chapter 11
Figure 11.5. Lava flows extend for several hundred kilometers across a fractured plain of Venus from the crater at the summit
of Sapas mons which is located at 8 N and 188 E on the western edge of Atla regio (Figure 11.3). This volcano has a
diameter of 400 km and its summit rises to 4,500 m above the mean elevation of Venus. The vertical scale of this image has
been exaggerated 10 times. The view is to the southeast toward Maat mons visible on the horizon. The coloration is based
on images recorded by Verena 13 and 14 of the USSR. The image (PIA 00107:Venus was produced by the Solar System
Visualization project and by the Magellan science team at the Multimission Image Processing Laboratory of JPL/Caltech and
was released during a news conference on April 22, 1992.(Courtesy of NASA/JPL/Caltech)
revealthatthelavasthatflowedfromtheirsummits
are bright as a result of surface roughness (e.g.,
Sapas mons in Figure 11.5 and Maat mons in
Figure 11.6). However, none of the volcanoes on
Venus erupted during the Magellan mission or
during any of the missions that preceded it. (Prinn,
1985; Fegley and Prinn, 1989).
Maat mons at the eastern end of Aphrodite
terra is the second highest volcano on Venus with
an elevation of about 8 km and a diameter of
395 km at its base. It occupies an area of about
122 480 km 2 , which is 1.15 times the area of the
state of Ohio 106 760 km 2 , and the average
grade of its slope is 4.0% (i.e., a rise of 4 m
for a horizontal distance of 100 m). The slope
of Maat mons is covered by lava flows that
reflect radar waves efficiently, suggesting that
they are young (i.e., less than 10 million years;
Freedman and Kaufmann, 2002, p. 249). The
physical dimensions of Maat mons are similar to
those of the volcano Mauna Loa on the island of
Hawaii (Section 6.4.4). Although the elevation
of the summit of Mauna Loa above sealevel is
only 4.0 km, its height above the surrounding
sea floor is 8.84 km. The slope leading to the
summit of Mauna Loa has a grade of 7.3%
measured from the coast (Moore and Chadwick,
2000). Therefore, the slope of Maat mons is only