Mountain Orogeny. Three types of plate boundary. ORIGIN OF MOUNTAINS. Orogeny = process of mountain building, takes tens of millions of years; usually produces long linear structures, known as orogenic belts. Two main processes: 1) Deformation : continental collisions, resulting in
ORIGIN OF MOUNTAINS • Orogeny = process of mountain building, takes tens of millions of years; usually produces long linear structures, known as orogenic belts • Two main processes: • 1) Deformation: continental collisions, resulting in • folding and thrust-faulting • 2) Volcanic Activity • Other processes: • Metamorphism, intrusions: batholiths, etc.
TYPES OF MOUNTAINS(according to their origin) • Fault-block: tension, normal faulting ex. Sierra Nevada, Wasatch, Grant Tetons • Folded: compression, reverse faulting ex. Appalachians, Alps, Himalayas, Urals, Atlas, Andes • Volcanic: Shield and composite ex. Cascades, Mid-Ocean Ridges, Oceanic Hot Spots * Dome Mts: similar to volcanic, Adirondacks, Black Hills • Complex: mixture of most of the above ex. Rockies, Alps, Himalayas
Organization of Mountains • Every mountain is part of a Mountain Range (ie. Green Mountains, Great Smoky, Blue Ridge, the Cumberland, White Mountains) • groups of ranges make up a Mountain System(ie. Northern Appalachian Mts.) • groups of systems make up Mountain Belts (ie. Appalachian Belt)
1. Fault-block mountains large areas widely broken up by faults Normal fault • Force: TENSION • Footwall moves up • relative to hanging • wall HANGING WALL
Tilted fault-block range: Sierra Nevada from east, Steep side of block fault; Ansel Adams photo
Tilted Fault-block Sierra Nevada from west Side, low angle Yosemite valley the result Of glaciation on low-angle relief Central cores consists of intrusive igneous rocks (granite). Half Dome is a core (batholith) that was exposed by erosion, Batholith
Wasatch Range From Salt Lake City Typically fault- Block system
Horst and graben Alternating normal faults lead to a characteristic pattern called a “horst and graben” system. An area under tension will often have multiple mountain ranges as a result.
Horst and Graben Landscapes Figure 12.14
Basin and Range province: • tilted fault-block • mountains in Nevada • result of a horst and • graben system • Nevada is under tension • because of rising magma • which is unzipping the • system, all the way from • Baja California Sierra Nevada and Wasatch Ranges part of this system
Reverse faults can also form Fault Block Mts. • Force: COMPRESSION • Hanging wall moves up • relative to footwall • Two types: • -low angle • -high angle Individual layers can move 100’s of kilometers Alps are a great example
Flatirons (Boulder, CO) Classic example of high-angle reverse faults -> Form “Sawtooth Mtns” due to differential erosion Seal rock
SAWTOOTH RANGE, IDAHO Alice Lake White Cloud peak
Folded mountains • Thrust (reverse) faults main • cause of folded mountains • Where rock does not fault it folds, • either symmetrically or asymmetrically. upfolds: anticlines downfolds: synclines
Zagros Crush Zone (Iran/Iraq) Alternating Anticlines and Synclines
Volcanic mountains • Shield • Gradual slope, very tall to ocean floor, slow flowing eruptions, composed of layers of lava • Composite (Strato-) • Explosive, made of pyroclastic material and lava. steep • Cinder cone • Very steep slopes, made of pyroclastic material,
Types of Volcanic Material • Pyroclastic material: rock fragments ejected from volcano • Ash: less than 2 mm in diameter • Dust: less than .25 mm diameter • Bombs: spinning cooling large blocks of material, cool to circular shape • Blocks: very large, as big as houses
Mafic Lava • Dark colored (when hardened) • Rich in Mg (magnesium) and Fe (iron) • Forms oceanic crust. • Mafic lava has a low viscosity and flows easily. • Seen in slow erupting Shield Volcanoes and hardening into Basalt (extrusive) or Gabbro (instrusive) • Dominant at Mid-Ocean ridges, Oceanic Hot Spots (Shield Volcanoes of Hawaii), Island Arcs and can be found at Rift Valleys, Continental Hot Spots (Yellowstone).
Shield volcanoes • gentle-sloping • basaltic lava flows At hot spots -Compressive forces -Mafic lava
Mauna Loa in Background Kilaeua is Behind Mauna Loa Mauna Kea Shield volcano Hot Spot Basalt
Felsic Lava • lighter colored (when hardened), rich in Si (silica). Forms continental crust. • Felsic lava has a high viscosity and DOES NOT FLOW EASILY. • Seen in continental Composite or Stratovolcanoes and result in EXPLOSIVE eruptions. Ex. Cascade Mts. and Mt. St. Helens. Can harden into granite (intrustive) and less likely rhyolite (extrusive). • Dominant at Oceanic: Continental Convergent plate boundaries/subduction zones and can be found at Continental Hot Spots (Yellowstone).
Composite (Strato-) volcanoes Encountered at subduction zones -andesitic composition -felsic lava -steep cones, explosive
Mt Rainier: example of composite volcano
Guagua Pichincha, Ecuador Quito in foreground Composite volcanoes explosive
Why do shield and composite volcanoes differ in composition? Mafic magmas rise along fractures through the basaltic layer. Due to the absence of granitic crustal layer, magmas are not changed in composition and they form basaltic volcanoes. Mountainous belts have thick roots of Felsic rise slowly or intermittently along fractures in the crust; during passage through the granite layer, magmas are commonly modified or changed in composition and erupt on the surface to form volcanoes constructed of granitic rocks.
Cinder Cones • Made of only pyroclastic rocks • Build cone-shaped hill • Most erupt only once • Low level eruptions • Paricutin, Mexico
Volcanism at Mid-Ocean Ridges • Majority of Earth’s volcanism • Hydrothermal vents • Chimney-like structures “Black Smokers” • Sulfur-bearing minerals or Sulfides • Incredibly diverse ecosystems, chemosynthesis
Importance of Volcanism • Eruptions can affect climate ex. Mt. Tambora eruption 1816 The Year Without Summer • Origin of life on earth Some theories suggest life began at mid-ocean ridges in chemosynthetic environments
Complex Mountains • continental-continental collision • tend to have a little of everything: volcanoes,folds, thrust faults, normal • faults
ALPS HIMALAYAS View of Everest and Khumbu ice fall from Kala Patar, Nepal Himalayas
Mountain orogeny summary • Orogeny = mountain building event • Plate tectonics used to explain mountain building • Plate collisions- 3 types: • Forces: tension, compression, shear • Mountain types: faulted, folded, volcanic, complex • Examples of each type • Types of volcanoes • Types of Lava • Importance of volcanism