Earthscapes
The Northshore
The Geology of
a Waterfall
by Bob Dvorak
Click on underlined words
for more information
 Crashing waterfalls. One of most beautiful features of nature
is caused when gravity takes its effect on water and pulls it down a cliff.
When someone thinks of waterfalls, images of tropical rain forests, hidden
valleys, and Niagara Falls comes
to mind, usually not Northeastern Minnesota. On the contrary, the Northshore
is home to many spectacular falls, most notably Gooseberry Falls.
Gooseberry Falls in located on the Gooseberry River. The falls run through
Gooseberry State Park forming an upper and lower falls. The river then runs
its course and ends up emptying into Lake Superior. 
The river varies in size and speed throughout the year. Heavy rains in
the spring and summer months can increase the discharge
of the river.
How are waterfalls formed?
Waterfalls occur at places in the river where the topography or height
changes. Water runs over a ledge and falls usually vertically to the next
level of the river. The ledges are usually made of a more resistant bedrock
layer, different from the rest of the river's parent material. In the case
of the Gooseberry, this parent material is gas-bubble basalt. The water running over the ledge cuts into the basalt
under the ledge  producing the falls and grade to the waterfall.
Eventually the erosional forces will undermine the ledge and cause it the
break off. This is what causes the upstream retreat of a waterfall. As this
action continues, eventually after many years, the waterfall will disappear
leaving only rapids as the trace it ever existed.
Chernicoff, Stanley, Fox, Haydn, and Venkatakrishnan,
Ramesh. "Essentials of Geology". Worth Publishers: New York, 1997.
 Back to the Northshore Earthscape
 
Disclaimer and Copyright
 Niagara Falls is one of the most renown regions
in the United States. It is commonly referred to the honeymoon capital of
the world. Niagara Falls divides the U.S. and Canada, each country having
their own city with the same name on either side of the Niagara River. The
falls stand 180 ft. high and 2200 ft. wide. Formed after the last ice sheet,
these falls have be eroding away rock for 12,000 years at a current rate
of 2 feet a year.
Picture courtesy of Rohit
Halbe
Back
 The discharge of a river is the
volume of water passing a given point per unit of time. As discharge increases
so does the velocity of the river. In this picture of the Gooseberry River,
the discharge is very high after a summer storm. Normally the island in
the middle of the river pictured here would protruding from the water by
about 8 to 10 feet. As discharge increases and levels rise, different rocks
are exposed to erosion for the first time.
Back
 Volcanic action millions of years
ago left the Northshore with a great amount of geologic sites. Large areas
of basalt from lava flows cover the landscape, materials are present in
many areas, especially rhyolite and taconite. The basalt seen here on the
Gooseberry River is very subseptible to erosion and allows for the great
falls one can view in the park.
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