Focus for Wednesday: Interpreting the Landscape of the Grand Canyon

Look at Landscape through different lenses—with different concepts

Geology, art, and geography interpret landscapes.

Art links geologic reasoning to place.

Grand Canyon by Thomas Moran

Vivid experience

Universal inthe particular

Place is a very important concept in geography.

The Strata of Place:Interpretation as Layers of Story

On Wednesday share your concepts for interpreting landscapes from:

• Physical Geography • Landscape Art

Also for Wednesday (class 5), complete the

“Convergent Plate Margin Tectonics and the Cascadia Subduction Zone”

concept map.

Tonight (Class 4):

Work with a partner:

1. Review Convergent Plate Boundary Maps.2. Make suggestions for improvements, clarifications.3. Create a map together limited to 7 or 8 important

concepts plus examples of objects, places, and events. Use nesting to limit the number of concepts.

4. Share the new map with the class.5. Learn about the Orphan Tsunami and Ghost Forest.6. Revise your personal map of Convergent Plate

Margin Tectonics and the Cascadia Subduction Zone: Add tsunami and turbidite concepts and examples for Wednesday (Class 5).

What is the asthenosphere?

The asthenosphere is• the hotter upper mantle below the lithospheric plate; • a viscoelastic solid (NOT liquid!!); and• can flow like silly putty.

USG

S G

raph

ics

See video links in notes

Three Basic Types of Plate Boundaries

Divergent

Convergent

Transform

USGS Graphics See video and animation links in notes

Divergent Plate Boundaries New crust is generated as the plates pull apart; Occur on ocean floors and continental interiors;

Earthquakes are shallow and small.

Fast-spreading RidgeExample: East Pacific Rise (moving apart at about 15 cm/year)

Slow-spreading RidgeExamples: Atlantic mid-ocean ridge Basin and Range, USAAfrican Rift ValleyNorthern Red Sea

Transform Plate Boundaries Lithosphere is neither produced nor destroyed as the

plates slide horizontally past each other.

Strike-slip fault—San Andreas Fault, California

Transform fault—a strike-slip fault between two spreading ridges allows the two plates to move apart.

Next slide: What is stress?

Convergent Plate Boundaries

Ocean /Ocean convergence (Marianas)

Ocean /Continent convergence (Cascades)

Continent/Continent Collision (Himalayas)

Plates push together. A) The denser plate subducts, or B) two continental plates crunch together and form high mountains.

Next slide: Why and where would earthquakes occur in convergent boundaries?

Earthquakes along Convergent Zones with Subducting Oceanic Lithosphere

Shallow earthquakes: The most destructive

of these occur between the plates on the plate

boundary.

Intermediate and Deep: Occur only within the subducting oceanic

lithosphere.

See animation & video links in notes

Young Subducting Plate

Old Subducting Plate

Island Arc Subduction Zone

Plate tectonics theory solved problems of:

• Fossil distribution and glacial deposits shared by antarctica, australia, africa, south america

• Mountain chains across North America, Europe, and Africa

• The “fit” of continents across oceans• parallel stripes of magnetism along ocean

ridges• The locations of volcanoes and earthquakes

Standard Model of Plate Tectonics:

• Rigid plates move due to convection.• Hot spot plumes are fixed.• Core heat maintains plumes.• Mantle is uniformly mixed. • Heating is from the bottom of the

mantle.

Alternative Model (“platonics”):

• Slabs of crust sink into the mantle and pull crustal rock behind them.

• Plates are not completely rigid and permanent.

• Earth’s outer shell is cracked and permeable.• chains of volcanic islands are zones of

weakness, not hotness.• Plates easily pull apart like schools of fish.• Gravity moves plates that are cooling at the

surface more than being heated from deep in the mantle.

Both Models:• The earth has hot spots and cold spots.• Hotter, warmer regions expand and rise.• Colder regions are denser and low.• Plates slide downhill from high warm regions to

cold, low ones on the earth.• They collide, sink, and scrape.• Plates slow the escape of heat from the earth—like

a blanket.• Warmed earth under a plate expands, stretches the

plate, and breaks it apart.• Plates are warm and buoyant when they form from

melted rock (lava).• Plates are cold, dense, and compact when they sink.