Catastrophic Flow Experiment

Homework 1_The Water Underneath:Groundwater

Julia Kahmann-Robinson PhD and Marjorie Chan PhD, University of Utah Department of Geology & Geophysics

Purpose

Observe the surface effects of groundwater seepage and apply these concepts to gulley or catastrophic flow features on Mars.

Preparation

This can be a bit messy, so it is good to have an area where there are sinks and clean up facilities.

1. Acquire some large plastic tub containers and fill them with loose sand to create a mini sandbox.

2. Have a supply of plastic ziplock bags (could try both quart and gallon size dependent on the size of the plastic tub and the amount of sand.

Engage

Have students look up groundwater sapping images of Mars (e.g., Noachis Terra) on the internet and examples on Earth.

Explore (Experiment)

Using the sandbox let's try to see if we can duplicate some of the features seen in the Martian photographs.

1. First, fill a gallon-size zip-lock plastic bag with water. Try not to leave any air in the bag.
2. Next, create a long low slope of wet sand in the sandbox.
   

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   Figure 1 Experiment set-up

   Provenance: Adapted from J. Weller Cochise College, AZ (2008)
   Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.
3. At the top of the slope bury the plastic bag of water so that one corner of the bag slightly sticks out of the slope.
   

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   Figure 2 Burying the bag of water

   Provenance: Adapted from J. Weller Cochise College, AZ (2008)
   Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.
   
   
4. Cover the bag with about one inch of wet sand. The water in the bag sloshes around; so smooth the surface above the bag so that there are no cracks at the surface.
5. Dust the slope with a very thin layer of dark dirt. This will help show the flow channel better.
6. With a pair of good scissors, quickly cut off about one inch of the exposed corner of the water-filled plastic bag, setting off the flood and collapse.

Explain

1. Did the rate of water outflow change the surface expression? Why or why not?

2. Consider a liquid with higher viscosity then water, for example taffy or molasses, that might be used in the bag. Would the surface expression change?

3. This hypothesis of groundwater sapping is considered by many researchers on Mars to be the cause of extensive deep channels and canyons present on the surface of Mars (think of Valles Marineris). Does this seem plausible to you? Why or why not?

Elaborate

Direct students to look at more detailed simulations of erosion and sapping to further explain channel systems on Mars.

Possible resources:

http://erode.evsc.virginia.edu/marssap.htm

Evaluate

Researchers propose that gullies and channels might be formed by the groundwater sapping. However, there could be more recent dry flows within the same channels.

See this HiRISE flyover video: http://www.youtube.com/watch?v=mgzl3l9bS_g