One way in which the Earth differs from all other
planets is the presence of abundant water on and within its surface. Water
in the three forms of matter (liquid, gas, and solid) make this planet
alive, both geologically and biologically.
Liquid water can cause massive changes to the Earth’s
surface through weathering and erosion of rock. It transports loose
material, wearing down mountains and filling in lakes and valleys. Liquid
water also helps plants grow, which may in term enhance erosion and
reshaping of the Earth’s surface.
Ice, in the form of glaciers and ice caps, is also a
powerful force of erosion and transportation. Ice is restricted to colder
areas (high altitudes and high latitudes), but it can cut through just about
anything. A glacier can carve its way through a mountain.
Wind is not as strong as water, but over a long period
of time it can also erode. In combination with water, wind can be more
destructive.
|
A close up of ice flowing downhill.
the dirty color is from sediment in the ice
|
A U-shaped ice cut valley. The ice is
flowing into the ocean
|
|
A V-shaped stream valley in Colorado, USA
|
This lab compares the two different ways that water
erosion works, as a solid (ice) and as a liquid. There are two parts in this
activity.
First, the students
compare a landscape created by snow and ice with one formed by running
water. This part of the activity uses portions of topographic maps.
Topographic maps record precise information about elevations on the Earth’s
surface. This appears on the map in the form of brown contour lines. These
are imaginary lines of equal elevation. Your students are unlikely to be
able to grasp the full concept of contour maps at this point. However, you
should explain to them that when contour lines are close together, the
landscape is steep (this is typical for glacial landscapes), and when
contour lines are far apart, the landscape is flatter. This is more common
in landscapes carved by liquid water.
In the second part of this lab students will explore
how ice acts as a cutting agent. They will see that ice can cut clay but
water cannot. Although this may seem obvious to you, it is often not to
students. Landforms created by glaciers tend to be U shaped, while landforms
created by rivers tend to be V shaped. The river concentrates its energy
just where the river is cutting, whereas a glacier cuts all areas that it
covers.
PROCEDURE:
|
Water flowing downhill in this stream
transports much material |
- Show the class pictures of the landforms created by
ice or running water. The web sites recommended below contain
many good examples. Alternatively, if they are available, show the class
models of different landscapes. These three dimensional tools are very
effective in explaining landscapes to children.
- http://geogweb.berkeley.edu/GeoImages.html/
- The Geo_Images Project at UC Berkeley. Contains abundant land and
aerial photographs of regions around the world.
- Gemorphology from Space, a NASA publication
featuring satellite and astronaut photographs. Clearly arranged by
process, with good global coverage.
The link is:
http://daac.gsfc.nasa.gov/DAAC_DOCS/geomorphology/GEO_HOME_PAGE.html/
- First, have them examine the maps. They should be
able to distinguish the glacial landscape by the presence of white areas
of ice and snow. This landscape should look steeper; there are many
places where the contour lines are very close together. The other map
shows a landscape carved by liquid water, shown by blue lakes and
streams. The landscape here should seem flatter to the students.
- Have the students set up the lab materials for
Exercise 2. They should work in pairs again. Make sure each student gets
a chance to experiment with the water and ice. Have them record their
observations.
Niagara Falls. An example of erosion by water |
-
Go over the student’s observations as a group.
You can also complete the conclusion as a group. The main point is for
the students to realize that ice is an important erosional force in cold
climates.
- You may want to describe frost wedging to the
students. In areas where it gets cold and then warms up during summer
you can "mechanically" weather rocks or roads. Water gets into
cracks in the road or rock. It freezes in the winter which expands the
crack (remember that water expands when it freezes). When the warm
weather comes and the ice melts, the crack is larger. As this process
repeats, the road or rock is gradually broken into pieces. Remind
students that when a can of soda freezes it can burst the can!
