Transcript Chapter 11 Mountain Building

Chapter 11 Mountain
Building
Section 11.1 Forces in Earth’s Crust
• Earth has 14 mountains over 8000 meters (~14,250 ft.)
Mt. Everest and K2 of the
Himalayan Mountains
Deformation of Rock
• Deformation – any change in the original shape and/or size of
a rock body. Every rock, no matter how strong, has a point
which it will bend or break.
• Most deformation occurs at plate boundaries where rocks are
subjected to stress and strain.
• Stress – the force per unit area acting on a solid. Rocks begin
to fold, flow, or fracture when subjected to stress greater
than their own strength.
• Strain – the change in shape or volume or a rock due to stress.
Types of Stress
Tensional
Compressional
Shearing
Principle of Isostasy
• Isostasy – concept of floating crust in
gravitational balance.
• Isostatic Adjustment – the process of establishing
a new level of gravitational balance.
• Newly formed mountains sink deep into the crust
due to their weight. As mountains weather and
erode away they become lighter, and the crust
rises in response. This is an example of an
isostatic adjustment.
Section 11.2 Folds, Faults, and Mountains
• During mountain building, compressional stresses
often bend flat-lying sedimentary and volcanic
rocks into wavelike ripples called folds.
• There are three types of folds – anticlines,
synclines, and monoclines.
• The Appalachian and Himalayan Mountains are
folded mountains.
Types of Folds
Anticlines
Upward fold of rock – an arch
Synclines
Downward fold in rock – a trough
Monoclines
Step-like Fold
Types of Faults
• Hanging Wall – rock surface immediately above
the fault.
• Footwall – the rock surface below the fault.
• The major types of faults are normal faults,
reverse faults, thrust faults, and strike-slip faults.
Types of Faults
• Normal Faults – occur due to tensional stress. The hanging wall
block moves down relative to the footwall. Found at divergent
boundaries. Angles are often 600
Types of Faults
• Reverse Faults – result from compressional stress. The hanging
wall block moves up relative to the footwall. High angle
faults > 450. Convergent boundary
Types of Faults
• Thrust Faults – reverse faults with angles less than 450. The
hanging wall goes up an over the footwall.Convergent boundary
Types of Faults
• Strike-slip faults – produced by shearing stress at transform
boundaries. The movement is horizontal and parallel to the
trend, or strike, of the fault.
Types of Mountains
• The major types of mountains include volcanic mountains,
folded mountains, fault-block mountains, and dome
mountains.
• Orogenesis – processes involved in mountain building.
• Mountain Range – several mountains of similar shape, age,
and structure. The Clinch Mountain Range is in this area.
• Mountain System – group of mountain ranges in the same
region. We live in the Appalachian system.
Types of Mountains
• Folded Mountains – caused by compressional forces found at
convergent boundaries that fold rock at reverse and thrust
faults. The Appalachian Mountains, the Himalayan Mountains,
and the Alps are some examples of folded mountains.
Types of Mountains
• Volcanic Mountains – vents in the Earth’s crust
that allow magma to come to the surface.
Types of Mountains
• Fault-Block Mountains – form as large blocks of crust are
uplifted and tilted along normal faults.
• Graben – block of crust that drops down due to normal faulting.
It creates the valley floor.
• Horst – blocks of crust that border the graben that stay uplifted
creating the mountains.
Landforms
• Up-and-down movements of the crust can produce a variety of
landforms, including plateaus, domes, and basins.
• Plateaus – broad, flat area of land uplifted to a relatively high
elevation. The Colorado Plateau is cut by the Grand Canyon.
• Domes – broad upwarped areas of land caused by laccoliths.
The Black Hills of South Dakota are an example.
• Basins – downwarped structures in the crust caused by plate
motions causing the crust to bend downward.
Section 11.3 Mountains and Plates
Convergent Boundary Mountains
• Convergent Boundary Mountains
• Oceanic-Oceanic convergence – when two oceanic plates collide, one
will subduct beneath the other resulting in a deep ocean trench and a
volcanic island arc. An example is the Aleutian Islands of Alaska.
Convergent Boundary Mountains
Oceanic-Continental Convergence – when they converge it can
produce inland volcanic mountains along with some folded
mountains.
Examples include the
Cascade Range, the
Andes of South America,
and the Coastal Range on
the West Coast of the
United States.
Convergent Boundary Mountains
• Continental-Continental Convergence – when two continental
plates collide folded mountains are formed. Examples include
the Appalachians and the Himalayas.
Divergent Boundary Mountains
• Most mountains are formed at convergent boundaries, but some
are formed at divergent boundaries along the mid-ocean ridges.
They are fault-block mountains made of volcanic rock.
Non-Boundary Mountains
• Some mountains do not form at plate boundaries. These are
volcanic mountains that form at a hot spot, a weak area in the
Earth’s crust. Fault-block mountains and upwarped(domed)
mountains can also form a long way from plate boundaries
Continental Accretion
• Accretion – this process enlarges continental landmasses and
forms mountains along the edges of continents. Pieces of crust
that collide with the continent become stuck or embedded in
the continental crust.
• Terrane – accreted crustal blocks.