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Storm in A Jar

written by:
Cam Tsujita
Department of Earth Sciences,
The University of Western Ontario


1 large (2 litre or more) plastic jar (such as a large peanut butter or pickle jar) or flat-bottomed plastic storage container
1 cup of sand
1 cup of mud (a well- mixed slurry of clay-rich soil and water will do)
1/2 cup seashells or pebbles
water to fill jar to about 5 cm from top

Place all ingredients in the jar.  Shake jar vigourously (this simulates turbulent conditions during a tropical storm).  Let contents settle (this simulates settling process as storm wanes) for about 1 hour.  After contents have settled, observe the sedimentation pattern in the jar.

After contents of the jar settle, you will hopefully note that the storm deposit is coarse-grained on the bottom (shells and gravel concentrated at base of deposit) and finer-grained on top (gravel overlain by sand and, in turn, by mud).  This sedimentation pattern, called "graded bedding" is evidence that can be used to recognize storms in ancient rocks.

Additional Comments:
Next time you see an outcrop of marine sedimentary rock containing fossils, look closely and see if you can recognize evidence of storms .