How the Great Lakes were formed.
About a billion years ago, a fracture in the earth running from
what is now Oklahoma to Lake Superior generated volcanic activity
that almost split North America. Over a period of 20 million years,
lava intermittently flowed from the fracture. This geomorphic age
created mountains covering the regions now known as northern
Wisconsin and Minnesota, and the Laurentian Mountains were formed
in eastern Canada. Over time these mountains eroded, while
occasional volcanic activity continued. Eventually the fracture
stabilized and, over time, the rock tilted down from north to
south.
The region went from fire to ice with the arrival of the glaciers,
which advanced and retreated several times over the last 5 million
years. During the periods of glaciation, giant sheets of ice flowed
across the land, leveling mountains and carving out massive
valleys. Where they encountered more resistant bedrock in the
north, only the overlying layers were removed. To the south, the
softer sandstones and shales were more affected. As the glaciers
melted and began receding, some lakes were created. Though the
original name of this glacial lake was Lake Algonquin. Over time
Lake Algonquin became Lake Huron and Georgian Bay.
Since the retreat of the glaciers, water levels continued to
undergo dramatic fluctuations, some in the magnitude of hundreds of
feet. These extremes were caused by changing climates, crustal
rebound and natural opening and closing of outlet channels. Within
the last 1,000 years, evidence suggests that lake levels exceeded
the range of levels recorded since 1865 by an additional five feet
on lakes Michigan and Huron. Many dune formations-some hundreds of
feet thick-were established during glacial periods. The tops of
these dunes have been continuously sculpted by winds to form the
majestic structures now visible.
Today, rebounding of the earth's crust, erosion, and changes in
climate continue to alter the shapes and sizes of the Great Lakes.
As one of the youngest natural features on the North American
continent, the lakes remain a dynamic, evolving system.
Lake Huron water level is more than 20 feet below that of Lake
Superior. There is an 8 foot difference between Lake Huron and Lake
Erie, Huron being the higher of the two. Lakes Michigan and Huron
are connected by the deep Straits of Mackinac and are considered to
be one lake hydraulically with lake levels rising and falling
together. Lake Huron is the third largest of the Great Lakes by
volume, holding nearly 850 cubic miles of water. The shores of
Huron extend more than 3,800 miles and are characterized by
shallow, sandy beaches and the rocky coasts of Georgian Bay. Lake
Huron is 206 miles wide and approximately 183 miles from north to
south. Home to many ship wrecks, the lake averages a depth of 195
feet. This lake is also the third largest fresh water lake on
earth.
This cache will take you to the beach in Port Sanilac. This will be
a nice place to visit and learn a little more about this
lake.
1. You will need a clear jar for a water sample. You will need to
cap and allow the water to settle at home for 3 days undisturbed.
Then e-mail a detailed description of has settled in the jar. You
are doing this to better understand the water of this lake. The
lake has a retention time of 22 years.
2. Being a deep glacial lake it will be interesting to see what the
changes in the temparture of the water. We can then chart the
change through out the year.
3. Very near the co-ordinance you will find a very large man made
structure. E-mail me what is there. 4. Post a photo of yourself
with this Great Lake in the back ground.
Thank you to
Beenhere for your help with the development of this
cache.
Be sure to e-mail me within 7 days of logging the cache to
get credit for your work. If the rules of finding an Earthcache and
e-mailing the owner is not followed your log will be deleted
without notice!