ELEMENTARY
ROCKS GET BROKEN DOWN AND
MOVED AROUND
National Science Benchmark
Waves, wind, water, and ice shape and reshape the earth’s land surface by
eroding rock and soil in some areas and depositing them in other areas.
Change is something that happens to many things.
From Benchmarks for Literacy from the American Association for the Advancement of Science.
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II: ROCKS GET BROKEN DOWN AND MOVED AROUND
PRE-ASSESSMENT – Rock, Where Did You Come From?
Materials per Student
• Paper and pencil
• Rocks
Procedure
Give each student a rock. Tell them, the rocks they have on their desks began
as a part of a larger rock on top of _________ (put an area here that fits your
area such as Ester Dome, a Chugach Peak, etc) and was found thousands of
years later at the _______ (put in an area near the starting point such as a
creek at the base of Ester Dome, Blueberry Hill, etc). Ask the students to write
or draw, how they think the rock got from where it started to where it landed?
Look to see if they tell both how it broke away and how it moved.
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ROCKS GET BROKEN DOWN AND MOVED AROUND
ROCK GET BROKEN DOWN AND MOVED
AROUND
Main Concepts
• Rocks are broken down and moved around by water, wind,
and ice.
• The surface of the Earth is always changing.
Lessons
Gear Up: Smooth Rocks
Wave Cans
River Runners
Rain Drops Keep Falling on My Head
Blowing It Around
Heaving Ice
The Great Glacier Race
Weighing Snow
Glacier Grind
Crashing Ice
Assessment 1: Broken Down and Moved Around Rock Hunt
Assessment 2: Rock Books
National Science Benchmark
Waves, wind, water, and ice shape and reshape the earth’s land surface by
eroding rock and soil in some areas and depositing them in other areas.
Change is something that happens to many things.
From Benchmarks for Literacy from the American Association for the Advancement of Science.
43
TEACHER BACKGROUND, WEATHERING AND EROSION
Erosion and weathering are often used synonymously; however, they are 2
different processes.
Weathering is defined as the decomposition or
disintegration of rock in place. These are both physical and chemical such a s
wedging (as with a plant’s roots or ice breaking up a rock), abrasion (2 rocks
rubbing together), and oxidation (rusting). Erosion is the process by which rock
and soil are moved downhill, downstream, or downwind. Erosion includes
both weathering and transportation of the weathered materials. For instance
rain pouring on soil may dissolve it and at the same time, move it downhill.
Alaska has vast coastlines, towering mountains, and enormous rainfall. The
state is also dotted with endless lakes, rivers, and streams. All of these forms
of water cause both weathering and erosion. The water flowing through
streams or rivers can wear away the shores, making cutbanks (weathering)
and it can move sand, silt, pebbles, rocks and even boulders (erosion). The
water can also flood, eroding soil and rock from the river banks (erosion).
Oceans act in much the same way, but the addition of their powerful waves can
so dramatically wear away rock it can create caves, ragged cliffs, and arches
(weathering and erosion). Water can also erode away the Earth through rain. If
the rain breaks down the soil it is known as weathering. When it moves the
soil downhill it is erosion. Powerful rainstorms in Southeast and Southcentral
Alaska can be so forceful that they can wash away soil and cause enormous
landslides.
Wind breaks down and moves Earth materials at the same time; therefore,
wind is a form of erosion. In Alaska the Kobuk Sand Dunes and the thick loess
deposits of the Fairbanks and Delta areas are all products of wind erosion.
The third type of weathering and erosion in Alaska is ice. If the ice wears away
rock or soil in place it would be considered weathering. Moisture caught in a
rock will expand when freezing and be strong enough to actually break or crack
the rock. If this happens over and over again, the rock will eventually break
apart. Also frost heaves are sedentary weathering where ice within the soil
causes the ground to expand and break apart. This is evident in sidewalks,
roads, or yards. In the spring students can actually see the frozen ice crystals
trapped in the mud along the sides of the roads and see how the ice breaks
the mud apart. Dramatic frost heaves, called pingos, can be seen in the
northern parts of the state. Pingos are ice cored frost heaves. They form and
grow under the influence of hydrostatic pressure within the near surface
permafrost layer. Their life span is measured in years. Once the ice core
surfaces and is exposed to sunlight and air, the core melts and the pingo
collapses. This weathering process can have significant effects on the soil
and sub-surface layers around it.
Ice is also an erosion agent as seen in the ice flows of rivers, lakes, oceans,
and glaciers. The ice on lakes, rivers, or oceans can crash against the shore
during breakup or freeze up, not only altering the shore, but carrying debris with
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it. The on-shore movement of sea ice can cause major modification to the
shoreline as well as significant changes in the sea bottom. Glaciers are
predominant in Alaska. After thousands of years of snowfall in which very little
melts, snow compacts under the pressure and eventually turns into a large
sheet of ice. This sheet of ice moves as the bottom layers melt due to extreme
pressures from above. As this happens, the glacier carrying bits and pieces of
Earth as abrasion tools, scrapes the rock bed on which it is sitting and
deposits debris along the way. (For more information on glaciers see pages
81-86).
There are very few ways which weathering and erosion can be stopped.
However, soil erosion can be minimized by the root systems of plants and
trees. These serve as an underground netting, holding the soil in place. When
trying to conserve, preserve, or reclaim land and its surface soils, the planting
of vegetation is the first thing done to help keep the soils in place.
It is not important that elementary students understand all aspects of
weathering and erosion as these topics will be dealt with on an advanced level
in the middle school version of Alaska’s Geology. It is only important, however,
that they know that water, wind, and ice are forces which break up and move
Earth materials.
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