M MOUNTAIN BUILDING Orogeny The Mountain Building Process

M MOUNTAIN BUILDING

Orogeny: The Mountain Building Process • What processes build mountains? 1) Volcanic activity 2) Tectonic Activity - Folding: Bending of rock -Faulting: Breaking of rock

Mountain Building • Mountain building processes thicken the crust • Mountains can be twice as thick as the average continental crust ( 70 km VS. 35 km) • Elevation of crust depends on thickness and density • Mountains have deep roots that extend into the mantle • As erosion occurs, mass is lost from the mountain and these roots begin to rise

Isostasy: Crust-Mantle Relationships • What is it? ~ Displacement & rebounding of the mantle by Earth’s continental and oceanic crust • Crust and mantle in equilibrium when gravity is balanced by the upward force • Isostatic Rebound: slow process of crust rising as a result of the removal of overlying material

Convergent Boundary Mountains • Oceanic-Oceanic: 2 oceanic plates; one descends into mantle, melts, then magma forced upward forming island arc which thickens to form root, displaces the mantle, forming mountain peak

Convergent Boundary Mountains • Oceanic-Continental: Plates come together, create subduction zone, produce major mountain belts due to the descending ocean plate forcing continental plate up; as crust thickens, higher and higher mountains form

Convergent Boundary Mountains • Continental-Continental: Creates tallest mountains (Himalayas); it is the energy from the collision of these plates that causes the crust to fold and fault; can double thickness of the crust

Divergent Boundary Mountains • Ocean ridges formed from rising convection cells that form in mantle; the divergent boundary bulges upward to form a gently sloping mountain range (longest on Earth) Mid-Ocean Ridge

Non Boundary Mountains • Uplifted Mountains: form when large regions of Earth have been slowly forced upward as a unit. (this concept is not yet completely understood)