Live From Mars was active July 1996-December 1997.
What Volcanoes tell us about a
All volcanoes are the result of heat and/or energy interacting with the stuff of which the planet is made. There are volcanoes both on Earth and Mars, but there are many differences as well as similarities. On Earth, volcanoes are a window through the planet's crust to the forces which move continents and raise mountains (plate tectonics). On Mars, they are windows on the past, evidence of a time when the Red Planet was unlike the world we see today.
The Volcanoes of Earth
On Earth, volcanoes occur either close to the boundary between plates (cone), or over hot spots under the crust (shield). These two types are characterized by very different eruptions and distinctive features, including shape, size, and slope angle.
The Volcanoes of Mars|
The Tharsis Bulge, located in Mars' northern hemisphere, is a huge dome, rising 10 km above the average elevation, and extending 4000 km from North to South, and 3000 km from East to West. It was probably created more than one billion years ago by the enormous pressure of molten material pushing up on the thin Martian crust. This also caused the giant cracks in the crust which can be seen around the Tharsis Bulge, the most impressive being Valles Marineris, Mars' "Grand Canyon."
There are a number of extinct volcanoes sitting on top of the Tharsis Bulge. They are all shield volcanoes, the largest of which is Olympus Mons. It is the largest volcano in the solar system, 3 times higher than Mount Everest, 2.7 times higher than Mauna Kea (from ocean floor to summit)--all this on a planet about half the diameter of Earth. Its huge size indicates two very important facts. First, the Martian volcanoes must have been active for a very long time (at least hundreds of millions of years). Second, they kept growing bigger and bigger, evidence that the Martian crust did not move much during all that time, indicating an absence of plate tectonics. In contrast, the chain of a hundred Hawaiian Islands shows us that Earth's crust kept moving over a hot spot under the Pacific. Instead of a single large volcano, we find a succession of volcanic mountains in a curving line which traces the motion of the plates.
Martian volcanoes provide important geologic data, but they also offer evidence used in the formulation of hypotheses on the past climate and atmosphere of Mars, and the controversial subject of life. If Martian volcanoes were active for a very long time, a great deal of gas would have been released into the atmosphere. This is part of the evidence that leads scientists to infer that Mars, in the past, had a thicker, warmer atmosphere. Now its thin atmosphere and the planet's deep freeze mean that liquid water cannot exist on the surface. But once, during that time when volcanoes were active, the planet could have been warm enough for liquid water.
For Each Team of Students|
and thick chocolate and butterscotch syrup
weighing at least several ounces
large Martian volcanoes
For Teacher Demonstration|
with a medium-large hole, one without a hole
general science or Earth science textbook)
Explain that students are going to investigate volcanic processes by modeling the formation of two types of volcanoes and measuring the resulting slopes. Procedure
1. Divide students into teams of "Planetary Geologists" and distribute a couple of large paper plates, protractor, string and a weight, and some sand, salt, dry rice and kitty litter to each team. Using a folded piece of stiff paper as a scoop, have students carefully drop sand from a height of 6 inches into the center of the paper plate (to simulate material forming a volcanic cone). Have students record what happens to the sand as they continue to pour.
Instruct students on how to connect their protractors, string and weights to measure angles. Have students measure the slope angle of the sand volcano they have just created. Record the results of each team on the board and have students calculate the average. Challenge students to predict what would happen to the slope angle of their volcanoes if they used more sand and made the pile higher. Have them do so and again record and average the results. Discuss.
Next, have students repeat their experiment using salt, rice and kitty litter. In each case, record and average the results and discuss. (Note: In all cases, the slope angles will probably average between 30 and 35 degrees and not be affected by the height of the cone or the materials used in the Activity.)
2. Show students pictures of cone-shaped volcanoes and have them measure the slope angles using their protractors. Record, average and discuss results.
3. Next, lead students in a discussion of shield or basaltic flow volcanoes and how they are formed. Stress that these volcanoes do not result from large quantities of material being shot high into the sky but instead gradually build up when "pahoehoe", a semi-fluid kind of lava, oozes out of the earth.
Using a clean paper plate, have students simulate this kind of volcanic formation by slowly pouring chocolate syrup into the middle of the plate. After a minute or two, have them measure the slope angle of this volcano. Record and average the results. Repeat with the butterscotch. (Students will note that the slope angles here are much gentler, typically only a few degrees.)
4. Show students pictures of volcanoes on Earth (e.g. the Big Island of Hawaii), but don't characterize them. Have students measure the slope angles. Record, average and discuss. Ask them what they conclude about these volcanoes.
5. Show students cross-sections of Olympus Mons. Again have them measure the slope angle. Record, average and discuss. Tell them these are characteristic of all volcanoes found on Mars and ask, as "Planetary Geologists," what they conclude about the nature of Martian volcanoes.
Based on this, challenge them to draw conclusions about the presence or absence of plate tectonics on Mars. Challenge them to suggest why Mars shows no evidence of plate tectonics.
6. Finally, distribute cross-sections of Olympus Mons and the Hawaiian Islands. Ask them to describe the difference in size. Challenge younger students to compare the difference in heights and base widths of these volcanoes. Challenge older students to estimate by calculation the difference in volume of these volcanoes. Challenge students to explain why the Martian volcanoes are much larger than those in the Hawaiian Island chain.
The Hawaiian Islands resulted from a crustal plate slowly moving over a hot spot and thus, over time, creating a succession or chain of volcanoes. Due to the absence of plate movements on Mars, hot spots remained for long periods of time under the same point in the crust and thus allowed the Martian shield volcanoes to build to a greater and greater size until Mars' interior cooled. Indeed, Olympus Mons is the largest extinct volcano in the solar system.
Connect Turn the discussion back to the theme of plate movements and relate the Martian volcanoes and their internal sources of heat to the formation of the Tharsis Bulge. Have students measure the total height difference between the top of Olympus Mons and the region of the Pathfinder landing site. Have students compare this to the difference in height between the top of Mauna Kea in Hawaii and Mt. Everest to the bottom of the Marianas Trench. Which is the "lumpier" planet and why?
Study of the canyons and valleys on Mars is an obvious extension here. Hands-on activities are available from JPL's Mars Exploration and Public Outreach Program, which is part of NASA's Mars Exploration Directorate.
For further information contact:
Dr. Cheick Diarra/NASA JPL
Create a 3-dimensional contour map of Tharsis Bulge.
Read about famous volcanic eruptions. Write a "You are There" article for a publication appropriate to the time in history.
Review angle measurement.