Volcanoes and/or lava flows are prominent features on all large rocky planetary bodies. Even some asteroid fragments show evidence of lava flows. Volcanism is one of the major geologic processes in the solar system. Mars has a long history of volcanic activity from the ancient volcanic areas of the southern highlands to the more recent major volcanoes of the Tharsis bulge. Olympus Mons is a volcanic mound on Mars that rises more than 20 km above the surrounding plains. This one volcano would cover the entire state of Arizona!

This topographic simulation shows Mars' Olympus Mons, the largest known volcano in the solar system. Image credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

Where volcanic heat and water interact here on Earth, scientists are finding life. In the hot springs of Yellowstone Park, for instance, they have found abundant life forms including some very small bacteria. There is a possibility that life may have found a place in the ancient volcanic terrain of Mars, too.

Some of the volcanoes on Mars are basaltic shield volcanoes like those on the Hawaiian Islands. Interpretations of photographs and soil analyses from the Viking and Pathfinder missions indicate that many of the lava flows on Mars are probably basalt. Scientists believe that basalt is a very common rock type on all the large bodies of the inner solar system, including Earth.

In addition to shield volcanoes, there are dark, flat layers of basaltic lava flows that cover most of the large basins of Mars and Earth’s moon. The eruption sources for most of the basin lava flows are difficult to identify because source areas have been buried by younger flows.

Generally, the overall slope of the surface, local topographic relief (small cliffs and depressions), and eruption direction influence the path of lava flows. Detailed maps of the geology of Mars and the moon from photographs reveal areas of complicated lava layering. The study of rock layering is called stratigraphy.

Older flows become covered by younger flows or become more pocked with impact craters on places with a thin or non-existent atmosphere, like the moon or Mars. Field geologists use differences in roughness, color and chemistry to differentiate between lava flows. Good orbital images allow them to follow the flow margins, channels and levees to try to trace lava flows back to the source area. Core samples, cylindrical sections that show various layers beneath an exposed layer, are obtained by drilling into the lava flows using special drill that has a hollow steel tube allowing for the extraction of subsurface matter.

Introduce volcanoes to students by explaining the various types of volcanoes and how eruptions occur. Show images of volcanoes and lava flows from ground-based, aerial, and  satellite perspectives. Examine recent activity using the Hawaiian Volcano Observatory and the USGS Volcano Hazards Program. Explain that volcanoes exist elsewhere in the solar system including the home of the largest known volcano in the solar system, Mars. Help students to understand the importance of learning geologic history to better comprehend the evolution of our planet and others. Also, point out that geologic processes involved in volcanic eruptions can dramatically influence the surrounding landscape and impact populations. Explain that in order to better understand these processes and the history of volcanoes students will create model shield volcanoes.

Part 1: Creating a Volcano

1. Cut the top of the small paper cup so that the cup is 2.5 cm high.


2. Place the small paper cup in the center of each piece of graph paper and trace around it with a pencil.


3. Secure the small paper cup (right-side up) onto the cardboard using a small loop of tape on the bottom of the cup. This short cup is your eruption source (eventual caldera) and the cardboard is the original land surface.


4. Mark north, south, east, and west on the edges of the cardboard and the graph paper, orienting them similarly on the table.


5. Fill about half of a large paper cup with baking soda.
   


6. Place one heaping spoonful of baking soda in the short cup.




7. Pour some vinegar into a second large paper cup.


8. You are now ready to create an eruption. Slowly pour a small amount of vinegar into the small, source cup and watch the eruption of simulated lava.




9. When the lava stops, quickly draw around the flow edge with a pencil.




10. Dab up the fluid with paper towels.




11. As best you can, use a thin layer of play dough to cover the entire area where lava flowed.




12. On one piece of graph paper, use a colored pencil that matches the play dough color to draw an outline representing the edge of the play dough, being sure to maintain the cardinal orientation (north, south, east, west) of the paper with the orientation of the volcano. Shade in this lava flow drawing. Make a note on the graph paper regarding the order of eruptions (which color came first).




13. Repeat steps 6 - 12 for each color of play dough available. Four to six flows show a good example of a shield volcano, but three flows will be adequate for a simple shield volcano model. Notes: The source cup may be cleaned out as needed. Be sure to mark the entire area of each lava flow – over previous flows and on the cardboard. On subsequent flows, you will need to dig into the underlying play dough with your pencil to mark the flow area. The result will resemble a strange layer cake with new flows overlapping old ones.




14. If time is short, cover each volcano with plastic wrap and return to the activity the following day.

1. Have teams trade volcanoes so that they can investigate and map a volcano with an unknown history. They may give the volcano a name if desired.


2. Explain to students that they are to act like planetary geologists who have just come upon this volcano and must determine its history and create an accurate map representing its formation.


3. Have students orient and label their blank piece of graph paper to match the cardinal (north, south, east, west) directions of their volcano.


4. Have students draw the visible layer(s) of the volcano to scale on the graph paper using a ruler and colored pencils.


5. Discuss that there is much detail that can't be seen from the surface. 


6. Answer the questions on the student worksheet. Note: Some volcanoes may be more complex than others. Each will be different! There may be flows that are completely covered, some flows that have two separate lobes, and some flows for which the sequential relationship cannot be determined at the surface.


7. Lead the students to question what they cannot see below the surface. Where do the flows extend under the exposed surface? Ask students to hypothesize how geologists investigate such hidden details. Then discuss various subsurface exposure techniques including core sampling, erosion cuts, road cuts, earthquakes, surface-penetrating radar, etc.
   


8. Have groups make a plan that shows on their map where they want to investigate the layers of their volcano using using the subsurface exposure techniques discussed above. They should indicate how the proposed cores and cuts will maximize the information they might gain from excavations. Limit the number of exposures each group may use, e.g., five drill cores and one road cut and one river erosion.


9. To make the cuts or cores on the volcano models:
   


• Remove a core sample by pushing a straw vertically into the play dough until encountering the cardboard surface, twisting if necessary, and withdrawing the straw. The various layers of play dough will be visible in the core sample inside the straw. Lay the straw containing the core sample next to the hole from which it was taken.




• River valleys may be made by cutting and removing a V-shape in the side of the volcano (open part of the "V" facing down slope).




• To make road cuts, use a plastic knife or dental floss to cut and remove a strip about 1-cm wide and as deep as you want from any part of the volcano.


• To make earthquake exposures, make a single cut and lift or drop one side of the fault line. Some support will be necessary.


10. Record cuts and cores on the map and in notes. Be sure to use location information, e.g., core No. 2 is located on the blue flow in the northeast quadrant of the volcano.


11. Observe hidden layers. Interpret data and draw dotted lines on the map indicating the approximate or inferred boundaries of the subsurface flows. Color in flow areas.


12. On a separate paper, have students write a short history of the volcano that relates sequence of flows and relative volumes of flows (or make a geologic column, a map key showing the history of the volcano with oldest geologic activity at the bottom and youngest at the top). Math classes may try to compute the volume of the various flows.


13. Compare the history developed through mapping in Part 2 with the original history from the group that made the volcano in Part 1. Have students write how they are similar or different.


14. Examine volcano maps created by geologists. How are these similar to and different from the maps students created for their volcano model?