Chapter 11. Volcanoes on Venus and Mars

11.1 Introduction

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Author: Janelle M. Bailey, University of Nevada, Las Vegas

Editor: Beth Hufnagel, Anne Arundel Community College

Venus
Venus, in false-color, from the Galileo spacecraft in 1990. Photo courtesy NASA/JPL-Caltech.
Mars
Mars as viewed by the Hubble Space Telescope in 2003. Courtesy of NASA, J. Bell (Cornell U.) and M. Wolff (SSI)

The goals of this module: At the end, you should be able to:

  1. Identify similarities and differences between the volcanic features of Earth, Venus, and Mars.
  2. Explain how these differences probably came about.

In this module you will explore:

  1. Topographical maps showing the tectonic surface features of Earth, Venus and Mars.
  2. Models of how the interior of a planet affects these surface features.

Why you are doing it: Comparison of other planets' volcanic features with those on Earth will help us understand not only how their surfaces differ, but also how the interiors of other planets are different from Earth's interior.

11.2 Background

Earth
Earth as it would appear without the oceans

Venus and Mars are our nearest planetary neighbors. Venus is sometimes called Earth's 'sister' planet, because of its similar size. Mars is the subject of intense robotic (and, in the future, manned) exploration. Like Earth, these two planets are small (compared to Jupiter!) and rocky. They all also orbit close to the Sun, but with Venus closer than Earth and Mars further away from Earth.

Earth has an active tectonic plate system, marked by volcanic mountain ranges where plates are colliding, such as the Cascades on the West Coast of North America, and the Himalayas of Asia. The Mid-Atlantic Ridge, stretching from Iceland to Antarctica, is a chain of underwater volcanoes resulting from oceanic plates spreading apart. When plates spread apart, rift valleys form, though volcanoes don't form there.

Plate Separation
The separation of two plates

Volcanoes are also seen in the middle of plates. Molten rock, magma, wells upward from a stationary hot spot in a planet's mantle and flows out to build a flattened volcano with sloping sides. This is called a shield volcano. As the plates move over the hot spot, a long chain of volcanoes is produced. The Emperor Seamount Chain, formed about 70 million years ago, is so eroded that none of it can be seen from the surface of the ocean.

Volcanoes are important, since they are clues to the nature of a planet's crust and mantle. Since volcanic activity changes the surface features over time, it also helps us determine the history of a planet. In this activity, you will examine volcanoes on Venus and Mars and how these features came about.

Volcanoes
Hot-spot volcanoes on Earth

11.3 A Look at the Surface of Venus

This topographic map, taken by the Magellan spacecraft's radar altimeter, shows details of the surface of Venus.

Topographic Map

Notice that the color shows elevations both above and below the planet's average surface height. The majority of the surface is blue-green, indicating that it has very little variation in its elevation. In fact, most of the surface is within 5 kilometers (km) of the average planetary radius, the distance from the center of the planet. Venus is too hot to have liquid water, so the blue does not mean seas or oceans! (Magellan did not map the gray areas - we have no information about the elevations in those regions.)

Question Sequence

Question 11.1

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3
Try again.
Correct. Venus's surface is much flatter on average than Earth's surface.
Incorrect. Venus's surface is much flatter on average than Earth's surface.

Question 11.2

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3
Try again.
Correct. There are a number of chasma on the surface of Venus that look like rifts on the Earth. You may also have noticed that this is the only significant type of tectonic feature on Venus!
Incorrect. There are a number of chasma on the surface of Venus that look like rifts on the Earth. You may also have noticed that this is the only significant type of tectonic feature on Venus!

11.4 A Look at the Surface of Mars

When you look over the entire surface, Venus is, overall, quite smooth. Not so the surface of Mars! Topographic maps of Mars, like this animation made from data from the Mars Global Surveyor spacecraft's laser altimeter, show that a greater amount of the surface varies from the planetary average.

This animation shows the topography of the Martian surface as measured by the Mars Orbiter Laser Altimeter (MOLA), an instrument on board the Mars Global Surveyor spacecraft. The colors indicate elevation: white is highest, followed by red, yellow, green, light blue, and dark blue (lowest). North is at the top.

Figure Caption
Mars Topography

Although there are more Martian surface features that stand above or below the planetary average, individual elevation differences are smaller than that of Venus. Notice that the highest points on Mars are only about 8 km above the average, as opposed to about 12 km on Venus. There is also a striking rift valley called the Valles Marineris, which runs parallel to the equator, colored in blue.

Rotate the Martian globe until you find the point where the features are colored white.

Question 11.3

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3
Reread the animation's caption for a key to reading the colors assigned to different elevations. Try again.
Correct. This area is called the Tharsis rise, and it contains several shield volcanoes. Near this region is Olympus Mons, the tallest volcano in the entire solar system.
Incorrect. This area is called the Tharsis rise, and it contains several shield volcanoes. Near this region is Olympus Mons, the tallest volcano in the entire solar system.

11.5 Under Venus's Crust

Like Earth, Venus has convection currents in its hot, liquid mantle. However, the crust of Venus is thinner than that of Earth and it is not broken into large plates. Rather than having plate tectonics, like Earth, Venus has flake tectonics that influence its surface features.

The Crust of Venus
Adapted from T. Grotzinger, T.H. Jordan, F. Press, and R. Siever, Understanding Earth, 5th ed., W.H. Freeman, 2007

The strong convection currents on Venus keep the crust from thickening. Instead, the currents cause the thin crust to crumple, creating 'flakes' in some areas. Between the currents, magma rises to the surface and creates mountains and other volcanic deposits.

From the resulting surface features and the low number of uniformly scattered impact craters, we know that Venus's entire surface must be about the same age. By calculating the time needed to create the observed density of craters, the volcanic activity that shaped the surface that we observe now is thought to have occurred about a half billion years ago.

Question 11.4

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3
Lava flows and new mountains cover up the old surface, including craters. Try again.
Correct. The flow of fresh magma over the surface covers up the old surface and any features like craters. Since Mars is densely cratered, this implies that Mars' volcanic activity ended billions of years ago. Since Venus has much fewer craters, this implies that it has a young surface.
Incorrect. The flow of fresh magma over the surface covers up the old surface and any features like craters. Since Mars is densely cratered, this implies that Mars' volcanic activity ended billions of years ago. Since Venus has much fewer craters, this implies that it has a young surface.

11.6 Hot Spots on Venus and Mars

Neither Venus nor Mars show evidence of plate tectonics like those that are observed on Earth. With the animation below, we can see what happens as the result of a hot spot with and without plate tectonics.

The animation will begin playing with plate tectonics. To view the opposite, click the button on the animation that says "Without plate tectonics"

Volcanoes on Venus and Mars

On this animation, select the "with plate tectonics" option and run the animation.

Question Sequence

Question 11.5

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3
Try again.
Correct. These chains of hot-spot volcanoes are seen on Earth, but not on Venus or Mars. Go on to the next option on the animation.
Incorrect. These chains of hot-spot volcanoes are seen on Earth, but not on Venus or Mars. Go on to the next option on the animation.

Question 11.6

Now select the "without plate tectonics" option and run the animation.

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3
Try again.
Correct. The hot spot gets 'stuck' in one place and the shield volcano keeps getting bigger until the crust gets too thick to let liquid through. This type of enormous shield volcano is seen on Venus and Mars.
Incorrect. The hot spot gets 'stuck' in one place and the shield volcano keeps getting bigger until the crust gets too thick to let liquid through. This type of enormous shield volcano is seen on Venus and Mars.

11.7 Quick Check Quiz

Indepth Activity: Volcanoes on Venus and Mars

Question 11.7

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Correct. This implies that the tectonic plates, if any, on Venus or Mars, are not moving.
Incorrect. This implies that the tectonic plates, if any, on Venus or Mars, are not moving.

Question 11.8

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Correct. There is an enormous rift valley on the surface of Mars.
Incorrect. There is an enormous rift valley on the surface of Mars.

Question 11.9

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Correct. Mars has the thickest crust since it has the biggest and oldest shield volcanoes. Earth still has moving plates and active volcanic features, but Venus's crust is flaked and crumpled due to the action of the mantle on the thin crust.
Incorrect. Mars has the thickest crust since it has the biggest and oldest shield volcanoes. Earth still has moving plates and active volcanic features, but Venus's crust is flaked and crumpled due to the action of the mantle on the thin crust.

Question 11.10

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Correct. Rather than having plate tectonics, Venus has flake tectonics that influence its surface features. The strong convection currents on Venus keep the crust from thickening, and the currents cause the thin crust to crumple, creating “flakes.’”
Incorrect. Rather than having plate tectonics, Venus has flake tectonics that influence its surface features. The strong convection currents on Venus keep the crust from thickening, and the currents cause the thin crust to crumple, creating “flakes.’”

Question 11.11

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Correct. Neither Venus nor Mars show evidence of plate tectonics like those that are observed on Earth. Hot spots on Venus and Mars have created huge shield volcanoes while on Earth shield volcanoes are smaller and are found in chains.
Incorrect. Neither Venus nor Mars show evidence of plate tectonics like those that are observed on Earth. Hot spots on Venus and Mars have created huge shield volcanoes while on Earth shield volcanoes are smaller and are found in chains.

Question 11.12

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Correct. Most of the surface of Venus is within 5 kilometers of the center of the planet.
Incorrect. Most of the surface of Venus is within 5 kilometers of the center of the planet.

Question 11.13

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Correct. Venus is only a half billion years old with a low number of uniformly scattered impact craters. Mars has many impact craters.
Incorrect. Venus is only a half billion years old with a low number of uniformly scattered impact craters. Mars has many impact craters.

Question 11.14

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Correct. Like Earth, Venus has convection currents in its hot, liquid mantle.
Incorrect. Like Earth, Venus has convection currents in its hot, liquid mantle.

Question 11.15

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Correct. The crumpling and flaking indicate that the crust is thin enough to be pushed and stretched.
Incorrect. The crumpling and flaking indicate that the crust is thin enough to be pushed and stretched.

Question 11.16

DVcaNcAo80tWLn3gv5lZjS7omZY6FyFQlOB/+8ro6eBXwVWfEpH4QAg0OZAi80FAPUdXEmStbOAKoJgcCDo7JHUxk31tubdc8Z18DrWt+rGy8mxVsyzRxR8h/K8qIKtnJzuC3KwXAP66xKuu0+WiO9/F/rY+8SrFAE63wWlir/A99ZjcJK4zZ3IytUp/cgAqeuNpSNmHTddhSnJoAxkfp1jGxOW1jm4ZPd2dscCzXVhJe9CV1JcnTgI7g7MSoDawuuYBEHQRaC1r+739iFryIXugtPa3V6SQ
Correct.
Incorrect.