count of 7 continents. This theory is called Continental Drift and it was
suggested by Alfred Wegener in 1912.
Convection currents is how heat moves in liquids. We find convection
currents inside the moho but we can also find convection currents in a pot of
boilling water. Convection currents are circles of heat side by side moving in
opposite directions.
When these happen inside the moho, many things can happen. At some
points on the earth parts of the crust can be sucked underground make cracks
on the ground. At other places on earth, the currents can push up the crust,
thus making a hill. Convection currents are what causes tectonic plates to
move. With out convection currents, there probably wouldn`t be any
continental drift.
As you learnt in the previous paragraph, convection currents take place
in the Moho. The Mohorovicic discontinuity is the boundary between the
crust and the mantle. The material inside the moho are smi molten rocks.
Most volcanic activity on the earth`s surface originate from the moho.
Laccoliths are a type of ignious formation. This means that these
mountains were formed as magma cooled beneath the surface, causing the
overlying rock layers to fold upwards. After the magma becomes rock, the
less durable rock above it erodes away leaving what we see today as
mountains. Mount Royal is a good example of Laccolith. People for a long
time thought that Mount Royal was an extinct volcano.
The Monteregian Hills extend for about 200 kilometres across the
St.Lawrence Plain and a part of the Appalachians. The hills are more
resistant rocks that stand above the sedimentary rocks forming the flat plain
of the Saint Lawrence Lowlands. Two of the Monteregian Hills are of
interest to mineralogists and mineral collectors, Oka Hills ans Mont St.
Hillaire. Contrary to popular belief, Mount Royal is not an ancient volcano
now extinct. This mistake is made because of the shape of the hill. Mont
Royal and some other monteregian hills have central depressions. A lot of
these depressions are occupied by a lake like Lac des castors on Mount
Royal and Hertel lake on Mont St. Hillaire. But these lakes are not crater
lakes and the rock that forms these hills is not volcanic! The Monteregian
Hills are examples of Laccolith.
Glacial Erosion is when several kilometres of ice melt, carving the rocks
around it often leaving lakes or valleys. Or even valleys in between
mountains. The Champlain sea was and example of Glacial erosion. About
450 million years ago, the Montreal, Ottawa area was part of a shallow
tropical seas with warm waters and coral reefs. As the earth changed and
continents collided, giant mountain ranges rose on each side of the region
and a valley was formed between them. Over time, the land rose and the
muck and mud became limestone. About five million years ago, climate
changes cause glaciers to move into the valley. These glaciers may have had
depths of a mile or more, filling the surface of the valley, their incredible
weight, increasing the valley`s depth. When the glaciers melted about 20 000
years ago, the melting ice left behing Lake Vermont, a big freshwater lake.
The glaciers to the north, wich were holding back the sea, melted enough for
the salty water to once again flood the region and the Champlain seas was
reformed. Around 11 000 years ago, with the giant weight of the glaciers
gone. The earth`s surface came back up and the champlain sea became
locked into the land, with no contact with the ocean. The salt water was
replaced with fresh water from the regions many streams. Eventually the
geography changed into what we know today as Lake Champlain and
Champlain Valley.
Isostatic adjustment is where earth`s shape is modified in response to
large scale changes in weight at certain places on the earth. The moho moves
around trying to relocate the magma that has been moved. 808 words
