Mountains and VolcanoesMountains and Volcanoes

MountainsMountains• Mountains are over 300 m in height and have

sloping sides.• Orogeny is the process of mountain building• Takes tens of millions of years; usually produces

long linear structures, known as orogenic belts

Two main processes that form mountains:1) Deformation: continental collisions resulting in folding and faulting.2) Volcanic Activity: opening in crust which allows magma to escape from below

Types of MountainsTypes of Mountains• Types are based according to their origin

• Fault-block: tension, normal faulting• Folded: compression, reverse faulting• Dome: magma pushing up on Earth’s crust• Volcanic: Shield and stratovolcano• Complex: mixture of most of the above

Fault-Block MountainsFault-Block Mountains

• Form at faults (plates slipping by).

• Edges of plates catch and push, which generates pressure.

• Pressure can cause earthquakes, or push parts of plate upward to form mountains.

Tilted fault-block range: Sierra Nevada from east,Steep side of block fault; Ansel Adams photo

•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

Folded MountainsFolded Mountains

• Form at convergent boundaries (continental-continental).

• One plate plunges into the mantle, while the other folds under pressure.

• ex) Rocky Mountains

and Himalayas.

http://www.geography.info/images/coco.gif

Rocky Mountains, BC.North American plate collides with Juan de Fuca plate

The Himalayas, Asia.Eurasian plate collides With Indian-Australian plate

Dome MountainsDome Mountains

• Form when magma from mantle rises and interacts with parts of the crust that won’t crack.

• Magma pushes section of crust up to form a dome.

• ex) Mount Royal, Quebec

http://www.montrealbb.ca/img/mont_royal.jpg

Volcanic MountainsVolcanic Mountains

Three types:

a) Shield volcanoes

b) Stratovolcanoes

c) Cinder cones

Shield VolcanoesShield Volcanoes• Found anywhere in a plate, not just

edges.• Form above hot spots in the mantle.• Magma collects in large pools and

eventually melts the rock above it and pours out through a hole in the crust.

Mauna Loa, Hawaii

Shield VolcanoesShield Volcanoes

• Magma that flows out is called lava.

• Lava is runny and flows like rivers.

• Hardens to form basalt rock.

• Hardens more quickly if occurs in ocean and forms cones.

• Shield volcanoes do not explode.

Mauna Kea

Mauna Loa inBackground

Kilaeua is Behind MaunaLoa

StratovolcanoesStratovolcanoes• Volcanoes that explode and blow ash and

rock everywhere!• Forms where two plates collide, one plate

slides under the other (subduction).• The descending plate heats up and melts,

magma rises and escapes through a hole in the top plate.

StratovolcanoesStratovolcanoes• Magma is thick and sticky.

• Water from descending plate heats up and forms steam.

• Steam increases pressure in volcano, which causes it to explode.

• ex) Mount St. Helens, Washington

Mount St Helens, 1980

Cinder ConesCinder Cones

• Built from lava fragments called cinders. 

• The lava fragments are ejected from a single vent and accumulate around the vent when they fall back to earth.

Status of VolcanoesStatus of Volcanoes

• Active – currently erupting or has erupted within the last 200 years

• Dormant – has not erupted recently (within the past few thousand years) but is considered likely to do so in the future

• Extinct – has not erupted for a very long time (tens of thousands of years) and is considered unlikely to do. Truly extinct volcanoes are no longer fueled by a magma source.

•Continental-continental collision•Tend to have a little of everything: volcanoes, folds, and faults

Complex Mountains

Orogenic BeltOrogenic Belt

• Long tracts of highly deformed rock

• Parallel strips of rock exhibiting similar characteristics along the length of the belt

ANATOMY OF AN OROGENIC BELT

Anatomy of an Orgogenic BeltAnatomy of an Orgogenic Belt

• Oceanic Plate: plate containing the ocean floor• Accretionary Prism: sediment collected at a

subduction zone• Igneous Arc: collection of igenous rock where

lava is cooling• Foreland: land that develops next to a

mountain/volcano• Craton: stable part of a tectonic plate found near

the middle of the plate