The Solar System

470 PART 4^ |^ THE SOLAR SYSTEM

Volcanism on Venus

Volcanism seems to dominate the surface of Venus. Much of
Venus is covered by lava fl ows such as those photographed by the
Venera landers (Figure 22-2). Also, volcanic peaks and other
volcanic features are evident in radar maps.
As usual, you can learn more about other worlds by compar-
ing them with each other and with Earth. Read Volcanoes on
pages 472–473 and notice three important ideas and two new
terms:

Th ere are two main types of volcanoes found on Earth.

Composite volcanoes tend to be associated with plate motion

and located near the edges of plates, whereas shield volcanoes

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APHRODITE TERRA

Artemis

Chasma

Alpha

Regio

Atla

Regio

Atalanta

Planita

Themis

Regio

Phoebe

Regio

Beta

Regio

ISHTAR TERRA

Lakshmi

Planum

Maxwell

Montes

Lowlands are colored blue, and

highlands yellow and red.

The old lava plains of Lakshmi

Planum are smooth and marked

by two large volcanic caldera.

The top of this volcano is

coated with a mineral that is

not stable on the lower slopes.

Maxwell Montes

is very rough.

■ Figure 22-5

Notice how these three radar maps show different things. The main map here shows elevation over most of the surface of Venus. Only

the polar areas are not shown. The inset map at left shows an electrical property of surface minerals related to chemical composition.

The detailed map of Maxwell Montes and Lakshmi Planum at right is color coded to show degree of roughness, with purple smooth

and orange rough. (Maxwell and Lakshmi Planum map: USGS; other maps: NASA)

are associated with hot spots caused by columns of magma

rising from deep in the mantle, and not by plate motion.

Notice that you can recognize the volcanoes on Venus and

Mars by their shapes, even when the images are manipulated

in computer mapping. Th e volcanoes found on Venus and

Mars are shield volcanoes, produced by hot-spot volcanism

and not by plate tectonics.

Also notice the large size of volcanoes on Venus and Mars.

Th ey have grown very large because of repeated eruptions at

the same place in the crust. Th is is also evidence that, unlike

Earth, neither Venus nor Mars has been dominated by plate

tectonics and horizontal crust motions.

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