Volcanic Activity on the Planet Venus

In fact, there is evidence both that there has been in the past considerable volcanic activity, and that there continues to be such activity. Pioneer Venus, the spacecraft which has been orbiting that planet since 1978, has been able to create a map of the geologic features of Venus with the use of radio waves and microwaves , and that map has clearly revealed "volcano-like structures" (Prinn, 1985, p. 46).

In addition, there is evidence that not only has there been volcanic action in the past, but that there is ongoing volcanic activity on the planet. That evidence comes in the form of a "thick, permanent layer of clouds" hanging over the planet, a cloud layer which prevented the direct camera sighting of the surface of the planet by instruments aboard Pioneer Venus. As Prinn writes, "the very permanence of the opaque clouds is strong, albeit indirect, evidence of active volcanism" (Prinn, 1985, p. 46).

There are two other pieces of evidence for the ongoing activity of volcanoes on Venus --- the presence of radioactive decay on the planet, and the presence of gasses on the planet which indicate such activity.

Both of the latter sources of evidence give us strong indications that volcanic activity is, indeed, contemporary. The evidence requires more immediate study of the planet than is available from radar studies, and that more immediate data comes from three landers: "Equ

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spreading and recycling may have occurred on Venus in the past or may even be occurring at limited rates at present . . . " (Saunders, et al., 1991, p. 251, 259). Not only have the differences and similarities between the volcanic activity of Earth and the volcanic activity of Venus been well-established, but the causes for such differences are also being clarified. In that context, Trego writes, "Shield volcanoes on Venus have overall diameters similar to those on Earth and Mars; however, the height of these volcanoes is much less than shield volcanoes on Earth and Mars. The highest shield volcanoes can be found on Mars. The best example of large Martian shield volcanoes are those found in the Tharsis region. The reason for low elevations of Venusian shield volcanoes [compared to those on Earth and Mars] is a shallow magma source in the crust of Venus" (Trego, 1991, p. 95). Trego also importantly clarifies some of the features of the relationship between volcanic activity on Venus and the nature of tectonics on that planet: "Ishtar Terra is an area of crustal thickening on Venus where compression tectonics and underthrusting processes have taken place. The thicker crust at Ishtar Terra creates a higher than normal topog
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Approximate Pages = 9 (250 words per page)