Download Mountain Building - Hicksville Public Schools

Isostasy
– Isostasy (Greek ísos "equal", stásis
"standstill") is a term used in geology to
refer to the state of gravitational
equilibrium between the earth's
lithosphere and asthenosphere such that
the tectonic plates "float" at an elevation
which depends on their thickness and
density.
– Parts of the crust will rise or subside (sink)
until stability is achieved
• For example:
– As a mountain erodes, mass is removed and
the crust beneath the mountain rises to
maintain equilibrium
– As sediment is deposited, the crust
subsides (sinks) beneath its weight
• The weight of the ice
pushes down on the
crust. When the ice melts
the crust “pop” back up
as the mantle rebounds
• This is an example of
isostasy.
The same thing happens
when a mountain erodes.
There is less weight
pushing down on the
mantle, so it rebounds.
Mountain Building
Orogony
• Cycle of processes that form mountain
ranges
• Mostly associated with converging plate
boundaries
Mountains
Most commonly form at
converging plate boundaries
• Ocean-Ocean
– Island arcs such as Japan and Indonesia
• Ocean-Continent
– Volcanic mountains such as the Andes
• Continent-Continent
– Folded and Faulted mountains such as the
Himalayas
Folded Mountains
Orogenies can also happen
far from plate boundaries
• Fault-Block Mts.
– Crust is broken up due to tensional forces
– Grand Tetons in Wyoming
Grand Teton Mt.
Dome Mountains
• Nearly circular folded mountain
• Individual isolated structures that
occur in areas of horizontal strata
Adirondack Mts.
Mt. Marcy, NY
(5344 ft. highest peak in the Adirondacks)
• Dome Mountains can also be formed from hot
molten material (magma) rising from the
Earth's mantle into the crust that pushes
overlying sedimentary rock layers upward to
form a "dome" shape.
• Unlike a volcano, the magma typically does not
reach the Earth's surface. Instead, the
magma cools underneath the surface and
forms the core of the mountains.
• Laccoliths
Algonquin Peak, 5115 ft.
2nd highest peak in the
Adirondacks
An example of a domeshaped mountain is Half
Dome in the Sierra
Nevada range in
California. It's made of
granite, and was once a
large blob of magma
pushed up through the
Earth. Granite is much
harder than other rock,
and so it doesn't erode
as easily as the rest of
the mountain. The
softer layers of
sedimentary rock were
washed away, leaving
the hard granite dome.