1. Mountains and Volcanoes

2. Mountains 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

3. Types 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

4. Fault-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.

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

6. 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.

7. Folded Mountains
Form at convergent boundaries (continental-continental).
One plate plunges into the mantle, while the other folds under pressure.
ex) Rocky Mountains
and Himalayas.

8. Rocky Mountains, BC.
North American plate collides
with Juan de Fuca plate
The Himalayas, Asia.
Eurasian plate collides
With Indian-Australian plate

9. Dome 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

10. Volcanic Mountains Three types: a) Shield volcanoes b) Stratovolcanoes
c) Cinder cones

11. Shield 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

12. Shield 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.

13. Mauna Loa in
Background
Kilaeua is
Behind Mauna
Loa
Mauna Kea

14. Stratovolcanoes
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.

15. Stratovolcanoes 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

16. Cinder 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.

18. Status 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.

19. Complex Mountains Continental-continental collision
Tend to have a little of everything: volcanoes, folds, and faults

20. Orogenic Belt Long tracts of highly deformed rock
Parallel strips of rock exhibiting similar characteristics along the length of the belt

21. ANATOMY OF AN OROGENIC BELT

22. Anatomy 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