Live From Mars was a precursor to Mars Team Online.
Activity 1.3: Follow that
Water--Investigations with Stream Tables
Water is essential to life on Earth: its abundant presence on our world
drives the weather and shapes the land by rain, runoff and erosion. Whenever
we see what looks like evidence of liquid water elsewhere in the Universe,
we become especially interested, since water is a requisite for life.
In the late 19th Century astronomers peered at Mars through telescopes
and saw lines stretching across its surface: Giovanni Schiaparelli, an
Italian, called them "canali" meaning "channels" or "grooves", which was
translated into English as "canals." Some interpreted these "canals"as
evidence of intelligent life, and even an advanced Martian civilization
capable of massive, planet-wide engineering projects. Now spacecraft have
looked close-up at Mars, and we know there are no canals built by a Martian
Corps of Engineers. But some of the channels do have shapes which look
much like those we see on Earth. While it's tempting to think of them
as dried-up river beds, most scientists think many of the channels resulted
from sudden releases of underground water or sudden melting of underground
ice, rather than from sustained rainfall and enduring rivers. How do we
know we're not fooling ourselves, or misinterpreting the data, as did
some of those 19th century observers?
Scientists use different methods to understand the conditions under
which the channels may have been formed. One method involves the use of
stream tables, to simulate different rates of flow, from gentle rivers
flowing for a long time, to sudden, massive floods. In this Activity,
students will have the chance to discover for themselves some of the characteristic
shapes created by differing volumes of water, flowing at different rates
("volume over time"). With "educated eyes"they can then turn to study
images of Mars and recognize the features and discuss the mechanisms which
might have caused them.
Teams of students will build simple stream tables and other needed
Students will vary the angle of the stream tables in order to
simulate different flow rates and compare the results.
Students will observe various features formed in a stream table
by flowing water and compare these model features to photos of real
features on Mars in order to make inferences about the possibility
of water channeling on Mars.
Materials: for each team of students
Please note: if these materials are difficult to secure, consider
using only one set for the entire class, and assigning a different
Planetary Geologist team per angle, and emphasizing the Image
Processing and Data Analysis process for those who must watch.
Although there will be less student hands-on time, it might be
better to do the Activity in this way rather than foregoing it
altogether, so important is the issue of water to Martian science
and mission planning.
Activity 1.3 Student Work Sheet
1 wallpaper tray (poke hole about size of a quarter in one end
so water can drain into a bucket)
two buckets of clean play sand
a third empty (catch) bucket
a one gallon plastic water jug
2 plastic funnels: one with a 1/4 in. opening and one with a
1/2 in. opening
several blocks of wood cut from 2 x 4s, each about 6 in.
a piece of string and a small weight
several stones that are flat on top and bottom, about1/2 to 1
inch in diameter and 1/2 to 1 inch high
plastic lids from 1-liter soda bottles
selected images of Martian surface features: 1, 2, 3
selected images of Earth, featuring dry river beds 1
(Note: The Live From Mars videos will feature such
images. More may be found in the slide set and the Explorer's
Guide to Mars poster, included in the LFM Teacher's Kit.)
Show students pictures or video of rivers and floods on Earth
(perhaps local occurrences in your region). Do they think such conditions
could exist on Mars today? Ask if they think Mars could ever have
had liquid water. Or consider the question of water on Mars through
a discussion on the possibility of life on Mars today in contrast
to the distant past. Discuss conditions that seem necessary for
life to develop. Cite the August 1996 announcement of the possible
discovery of ancient Martian life in a meteorite.
Explore / Explain
Please note: some details are provided on the Student Work Sheet
and its diagram, which you should review along with this procedure.
1. Distribute materials to each student team. Explain that each
team is going to work as Planetary Geologists to investigate what
can happen to a surface when water flows across it, and that they
will share their data to come up with some principles by which water
shapes landforms in specific ways.
2. Demonstrate stream table set up and use of the protractor to
align the stream table at a given angle. This table should initially
be set at an angle of 5 degrees.
Students will see that at angles of about 15 degrees and higher,
the sand will wash out. Larger volumes of water over shorter time
periods (e.g. flood conditions) carve deeper channels with steeper
sides. Only at angles of around 5 degrees, simulating gentler processes
(e.g. slower flow over longer times) does the water begin to create
curves and meanders more typical of terrestrial rivers. Remind students
that most stream beds have slopes that are typically 5 degrees or
less but that in this simulation the angle stands for flow rate,
not the underlying topography of the planet. Also note that, as
in most simulations, you can't replicate all aspects of the original
condition you're trying to understand: for example, results obtained
by using sand do not perfectly model rivers running through soil
or over rock. But varying the angle does simulate flow rate, one
key variable scientists think important for Mars.
Pour 1 quart of water into the 1/4 inch funnel and allow the water
to run down the tray through the groove as the teams watch. Have
students describe and sketch the flow pattern which results, carefully
noting such things as the shape of the flow pattern including
- whether the channel cut by the water was straight or curved
- how wide the channel became
- how deep the channel became
- how long it took for the jug to empty
- was a small or large amount of sand carried down stream by
- whether or not avalanching occurred
- whether or not a delta was formed
3. Assign each team a slant angle (from 5 to 25 degrees) and allow
time for basic set up. For the first set of trials, each team should
use the plastic funnel with the 1/4 in. opening. Teams should complete
Trial # 1 and record results on the Student Worksheet.
4. Before continuing, allow time for teams to contrast and compare
results from the stream tables set at different angles. Discuss.
5. Smooth the damp sand back to a uniform layer. Then repeat the
same experiment at the same tray angle, but this time using the
funnel with the 1/2 inch opening. Repeat Steps 3-4.
6. Again, smooth the sand. Repeat the experiments, but this time
tell students to place the stones and the small bottle lids in the
tray in such a position that the stream of water will encounter
them, working them into the sand and adding a thin layer on top.
(This simulates what happens when flowing water meets the elevated
rim of an impact crater.) Have students carefully observe and record
the appearance of the patterns in the vicinity of the bottle caps
and stones at the end of the experiments.
7. Challenge students to answer the following questions:
At what slope angles (flow rates) do meanders and deltas occur?
At which slope angles (flow rates) does the sand wash out completely?
How does the slope angle (flow rate) affect the amount of sediment
deposited down stream?
What happens to the sand immediately after the water starts flowing?
What happens to the sand after the water has flowed for awhile?
What effect does the volume of water that flows per second have
on all of the above?
8. As a last activity, simulate a large scale catastrophic flood
by filling the gallon jug with water and carefully creating a uniform
"waterfall" along the top of the stream table. Have students try
with and without the stones and bottle lids in the flow. Again record
and discuss results.
9. Finally, refer to Viking images of Mars. Ask students to
look carefully at each one and challenge them to compare examples
of the different types of patterns they created in their stream
table experiments with what they see in the actual images of Mars.
Ask them to draw conclusions about the presence of water on Mars
in the past and to draw general conclusions about the differing
amount and rate of flow of water in the various areas on Mars
seen in the images. Ask them to search for signs of liquid water
on Mars in the Viking images (i.e., on Mars today). Challenge
them to hypothesize where they think all the water went.
Research the various theories as to how water was released onto
the Martian landscape at various times in the past and where scientists
think it is today.
Have students examine a map showing the geological surface features
over the entire surface of Mars. Have them mark the location of
outflow channels. Have them do the same with the location of valley
networks. Ask them to describe the differences in their geographical
distribution and challenge them to explain the reasons for this.
Provide students with the prime landing site for Pathfinder as
well as the coordinates of the Viking 1 and 2 landing sites. Ask
students to describe these locations relative to the location of
outflow channels and valley networks. Challenge them to hypothesize
why scientists chose these particular locations to put spacecraft
down on the surface of Mars.
Research meandering streams. What is an oxbow lake and how is
it formed? Why does a river bed change over time? Compare and contrast
each terrestrial feature to landforms on Mars.
Go on-line and download Mars images. Create a visual display illustrating
the various landforms on Mars. If you or your students have documented
the flow table experiments, prepare poster displays relating flow
rate to surface feature (and submit to Passport to Knowledge on-line
or in hard copy!)
Read about Giovanni Schiaparelli. Compose a letter he might have
written (or e-mailed) to NASA regarding his concerns about the veracity
of new data coming from Mars.
Write a news article about the stream bed simulations and report
on your data.
Noting the scale of the map, have students measure and calculate
the area of some prominent Martian outflow channels. Compare these
areas to related places on Earth such as the Nile River Valley,
the channeled Scablands region of Washington State or an area of
their home state.
Research the Scablands region of Washington State.
Note: this Activity and Activity 2.2 are adapted in part
from materials and concepts developed during workshops held by JPL's
Mars Exploration Directorate as part of its Education and Outreach
Initiative (Meredith Olson, Project Educator.) Related Activities
may be found in the series of Student and Teacher Publications created
by JPL: to order, contact TERC at 617-547-0430. The first two JPL-TERC
modules and a set of Mars and Earth images are part of the LFM
Teacher's Kit. LFM thanks Dr. Olson for her review of the
adaptations of the original activities.