Plate Tectonics

Continental Drift

Historical Landmass Locations

Fossil Evidence Supporting Plate Tectonics

Developing the Theory

• (1) demonstration of the ruggedness and youth of the ocean floor;

• (2) confirmation of repeated reversals of the Earth magnetic field in the geologic past;

• (3) emergence of the seafloor-spreading hypothesis and associated recycling of oceanic crust; and

• (4) precise documentation that the world's earthquake and volcanic activity is concentrated along oceanic trenches and submarine mountain ranges.

Developing the Theory (continued)

• (1) demonstration of the ruggedness and youth of the ocean floor.

• (See next slide)

Computer-generated topographic map of

Mid-Oceanic Ridge.

Mid-Ocean Ridge

Magnetic striping and polar reversals

Concentration of Earthquakes

Plate Motions

• There are four types of plate boundaries: • Divergent boundaries -- where new crust is generated as

the plates pull away from each other. • Convergent boundaries -- where crust is destroyed as one

plate dives under another. • Transform boundaries -- where crust is neither produced

nor destroyed as the plates slide horizontally past each other.

• Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.

Types of Plate Boundaries

Divergent Boundaries

Mid-Atlantic Ridge Example

Red triangles denote active volcanoes

Aerial view of the area around Thingvellir, Iceland, showing a

fissure zone (in shadow) that is the on-land

exposure of the Mid-Atlantic Ridge.

Divergent Boundary – East Africa

Map of East Africa showing some of the historically active volcanoes(red triangles) and the Afar Triangle (shaded, center) -- a so-called triple junction (or triple point), where three plates are pulling away from one another

Summit Crater of 'Erta 'Ale (Ethiopia)

Oldoinyo Lengai, erupts in 1966

Convergent BoundariesOceanic-continental convergence

Convergent Boundaries (example)

Oceanic-oceanic convergence

Continental-continental convergence

Continental-continental convergence

The collision between the Indian and Eurasian plates has pushed up the Himalayas and the Tibetan Plateau

Continental-continental convergenceIndian – Eurasian Plates

The Himalayas: Two Continents Collide

The 6,000-km-plus journey of the India landmass (Indian Plate) before its collision with Asia

(Eurasian Plate) about 40 to 50 million years ago. India was once

situated well south of the Equator, near the continent of

Australia.

Transform Boundaries

The Blanco, Mendocino, Murray, and Molokai fracture zones are some of the many fracture zones (transform faults) that scar the ocean floor and offset ridges (see text). The San Andreas is one of the few transform faults exposed on land.

San Andreas fault

Aerial view of the San Andreas fault slicing through the Carrizo Plain in the Temblor Range east of the city of San Luis Obispo.

Plate-boundary Zones

Rates of Motion

• The Arctic Ridge has the slowest rate (less than 2.5 cm/yr)

• The East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate (more than 15 cm/yr).

Hotspots: Mantle Thermal Plumes

Prominent Thermal Hotspots

The Long Trail of the Hawaiian Hotspot

Map of part of the Pacific basin showing the volcanic trail of the Hawaiian hotspot-- 6,000-km-long Hawaiian Ridge-Emperor Seamounts chain.

Plate Tectonics & People

• Natural hazards– Earthquakes

– Volcanic eruptions

– Tsunamis

• Natural resources – Fertile soils

– Ore deposits

– Fossil fuels

– Geothermal energy

Earthquakes

Aerial view, looking north toward San Francisco, of Crystal Springs Reservoir, which follows the San Andreas fault zone.

Earthquakes (continued)

Map of the San Andreas and a few of the other faults in California, segments of which display different behavior: locked or creeping

Fault Creeping

Left: Creeping along the Calaveras fault has bent the retaining wall and offset the sidewalk along 5th Street in Hollister, California (about 75 km south-southeast of San Jose). Right: Close-up of the offset

of the curb.

Earthquakes & Volcanoes

• Christopherson TextChapter 12 pp 375-end-of-chapter

What Causes Earthquakes?

Epicenter and Focus

• Focus  – Location within the earth where fault rupture

actually occurs 

• Epicenter  – Location on the surface above the focus

Types of Faults

Faults are classified on the basis of the kind of motion that occurs on them

• Joints - no movement

• Strike-slip - horizontal motion (wrench faults)

Types of Faults

•Joints - No Movement

•Strike-Slip - Horizontal Motion (Wrench Faults)

Joints - No Movement

Left Lateral Strike Slip

Right Lateral Strike Slip

San Andreas21 feet in 1906

Dip-Slip - Vertical MotionNormal Fault (Extension)

Alaska, 1964 - up to 150 Ft

Reverse or Thrust Fault (compression)

Eastern North America Earthquakes 1534-1994

U.S. Earthquakes, 1973-2002

Seismic Risk Level Maps for the U.S.Probable ground acceleration in 50 years.

Blue = small, red = large

Seismic Risk Level Maps for the U.S.Probability of Damage in 100 Years.

Blue = Negligible, Green = Low, Red = High.

M 7.9 Earthquake on November 3, 2002

• The largest earthquake known to occur in the world this year struck central Alaska on Sunday, November 3. The epicenter of the Nov. 3 temblor was located approximately 75 miles south of Fairbanks and 176 miles north of Anchorage. It struck at 1:12 PM local time, causing countless landslides and road closures, but minimal structural damage and amazingly few injuries and no deaths.

M 7.9 Earthquake on November 3, 2002

• Overall, the geologists found that measurable scarps indicate that the north side of the Denali fault moved to the east and vertically up relative to the south. Maximum offsets on the Denali fault were 22 feet at the Tok Highway cutoff, a road that goes from Tok to Glenallen and intersects with the Alaska Highway, and were 6.5 feet on the Totschunda fault.

• This earthquake is one of the largest ever recorded on U.S. soil and the largest seismic event ever recorded on the Denali fault system.

Denali Fault Earthquake

Rock Avalanches Across Black Rapids Glacier

Alaska Earthquake Pictures Taken by Local Resident

Alaska Earthquake Pictures Taken by Local Resident

Alaska Earthquake Pictures Taken by Local Resident

Alaska Earthquake Pictures Taken by Local Resident

Alaskan Pipeline

Northway Road - 4th of

November 2002

Road Offset, Richardson Hwy

Volcanoes

Two expressions of volcanic activity.

Volcanic fountaining in Hawaii.

Kilauea landscape.

Mt.Etna, Sicily – July 2001

Mt.Etna, Sicily – July 2001

Mt.Etna, Sicily – July 2001

Mt.Etna, Sicily – July 2001

Mt.Etna, Sicily July 2001

Mt.Etna, Sicily – July 2001

Mt.Etna, Sicily – July 2001