The Solar System

474 PART 4^ |^ THE SOLAR SYSTEM

occur on Venus as they do on Earth, the areas north and west of

Lakshmi Planum appear to be ranges of wrinkled mountains

where some type of horizontal crust motion has pushed up

against Ishtar Terra. Furthermore, faults and deep chasms are

widespread over the surface of Venus, and that suggests stretch-

ing of the crust in those areas. So, although no direct evidence of

plate motion is visible, there has certainly been compression and

wrinkling of the crust in some areas and stretching and faulting

in other areas, suggesting some limited crustal motion.

While Earth’s crust has broken into rigid moving plates, the

surface of Venus seems more pliable and does not break easily

into plates. Th e history of Venus has been a fi ery tale, dominated

by volcanism.

■ Figure 22-8

Volcanic features on Venus: (a) Arrows point to a 600-km (400-mi)

segment of Baltis Vallis, the longest lava-fl ow channel in the solar

system. It is at least 6800 km long. (b) Aine Corona, about 200 km

(120 mi) in diameter, is marked by faults, lava fl ows, small volcanic

domes, and pancake domes of solidifi ed lava. (c) This perspective

view shows a hill typical of those associated with a corona. Molten

lava below the surface appears to have pushed up the hill, causing

the network of radial faults. (d) Other regions of the crust appear to

have collapsed as subsurface magma drained away. (NASA)

Pancake

domes

Lava flows

a

Radar maps

Volcanic

domes

Coronae

b

50km (30mi)50km (30mi)

c

d

rock below the surface. All of these volcanic features are shown
in ■ Figure 22-8.
Th ere is no reason to suppose that all of the volcanoes found
on Venus are extinct, so volcanoes may be erupting on Venus
right now. However, the radar maps caught no evidence of actual
eruptions in progress.
If you want to learn more of the secrets of Venus, you will
want to visit the big land mass called Ishtar Terra. Western Ishtar
consists of a high volcanic plateau called Lakshmi Planum. It
rises 4 km (2.5 mi) above the rolling plains and appears to have
formed from lava fl ows originating in volcanic vents such as
Collette and Sacajawea (see Figure 22-5). Although folded
mountain ranges showing widespread plate tectonics do not