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 Synclines Monoclines Upward fold of rock – an arch Downward fold in rock – a trough 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 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.