This material was developed for the Live From Mars project by Passport to Knowledge. Live From Mars was a precursor to Mars Team Online.

Teachers' Guide

Activity 2.2: Reading the Shapes of Volcanoes on Earth and Mars

What Volcanoes tell us about a Planet
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.
Cone-shaped volcanoes (such as Mt. Shasta or Mt. Rainier in Washington State's Cascade Range, or Mt. Fuji in Japan, one of Earth's most perfect cones) erupt close to the leading edge of a continental plate. The ash and rock particles spewed into the air by explosive eruptions form the cone which is characterized by a narrow base and steep sides which typically have slope angles of about 30 degrees.
Shield or basaltic flow volcanoes result from successive flows of very fluid lava over hot spots under the planet's crust. These create gently sloping domes and typically have slope angles of less than 7 degrees. The Hawaiian Islands are the best example of these. The angle of a volcano's slope is a clue to whether plate tectonics were involved in its formation.
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.

Objectives:

Students will model the different processes which create cone and shield volcanoes.

Students will identify the kind of volcanoes that exist on Mars (shield) and relate this to the presence or absence of plate tectonics.

Students will be able to explain why Olympus Mons is the largest volcano in the solar system, and what its size allows us to infer about conditions on early Mars.

Students will demonstrate the ability to compare and contrast the volcanoes of Earth and Mars.

Students will measure and compare the slope angles of cone and shield volcanoes to differentiate between the two types.

Materials

For Each Team of Students

several cups of clean play sand, kitty litter
and thick chocolate and butterscotch syrup

several large paper plates

a protractor

a piece of string

a metal bolt or other small object
weighing at least several ounces

cross-sections of Olympus Mons and
large Martian volcanoes

pictures of cone shaped volcanoes on Earth
For Teacher Demonstration

3 small Pyrex test tubes (app. 18 x 150 mm)

3 cork stoppers: one with a small hole, one
with a medium-large hole, one without a hole

safety goggles

a candle or burner

an insulated test tube holder

a small amount of water

several Alka-Seltzer tablets

world map

graphic showing plate boundaries (from
general science or Earth science textbook)

Engage

Perform the following series of demonstrations in front of the class. (Wear safety goggles and point the test tube away from students. Glass could shatter when heated--please take necessary safety precautions.) Ask students to write a brief description of what they observe in each demonstration.

First pour a small amount of water into a test tube and add a ground-up Alka-Seltzer tablet. Have students record their observations. (The chemical interaction of water and tablet releases gases.) Discuss what happened and challenge students to predict what would happen if the open end of the test tube were partially blocked.

Place a small amount of water in a second test tube, again add a ground-up Alka-Seltzer tablet, but this time quickly place the stopper with the larger hole in the tube. Have students record their observations and discuss. Challenge them to predict what will happen if the vent hole in the test tube is even smaller. Clean the test tube and repeat using the stopper with the smaller hole.
Have students predict what would happen if the end of the test tube were completely plugged and ask them to brainstorm and list the geological process being simulated in this demonstration.

Explain that a planet's internal heat can be a very significant source of pressure. Complete the demonstration: place a small amount of water in a test tube, plug it with the cork without a hole, and heat the test tube over the burner. (Move the tube through the flame to minimize possibility of cracking.) As the water temperature increases to the boiling point, challenge students to explain what's happening inside the test tube, and what will eventually happen to the cork.

After the cork flies off, discuss the results, and challenge students to relate this to explosive eruptions of volcanoes such as Mt. St. Helens or Mt. Vesuvius. Students should realize that the cones of such volcanoes build up when the erupted materials fall back to earth and gradually pile up around the vent hole.

Ask students to name famous volcanoes and mark them on a map. Discuss where such volcanoes are located and why. Encourage students to note the clusters of volcanoes and brainstorm why they are not randomly distributed. This should lead to a discussion of plate tectonics, and the formation of cone volcanoes relatively close to plate boundaries.
Vocabulary
angle
atmosphere
cone
dome
extinct
geology
plate tectonics
pahoehoe
pressure
shield
slope
topographical map
volcano

Explore/Explain
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.
Expand/Adapt/
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
Mail Stop 180-401
4800 Oak Grove Drive
Pasadena, CA 91109
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.
$math icon$ Review angle measurement.