Sinking Slabs and Convection ConnectionsExplore: p. 672 - 678

Learning Targets

• I can use simple models to simulate the forces acting on tectonic plates.

• I can compare directions of plate motions with locations of hot spots, spreading ridges, and trenches

• I can determine the velocity of the North American Plate relative to the Yellowstone hot spot

• I can examine the depth-distance relationship for earthquakes in a subduction zone.

Entry Task

• What do you remember about the relationship between density and temperature from IS1?

• What happens to the density of a substance as it is heated?

• What happens to the density of a substance as it cools?• How do differences in density cause substances to rise or

fall?

Process & Procedure p. 672

• Read Introduction on pg. 672• #1. Video Demo• #1a. – d. Answer in your science notebook.

Process & Procedure p. 672

• 2. Read the paragraph. Take notes on anything that is new to you – especially vocabulary: mantle, plume, upwelling, hot spots, mantle convection.

• 3. Which part of your sketch represents upwelling? Downwelling?.

Process & Procedure p. 672

• Mantle – the layer of Earth that lies beneath Earth’s crust.

• Plume – a rising column of heat. Plumes occur in the mantle where hot material moves upward from the lower mantle, in some cases, to erupt at Earth’s surface.

• Upwelling – refers to the upward motion of material in plumes through the mantle.

Process & Procedure p. 672

• hot spots – outpouring of molten rock (lava) at volcanoes caused by plumes of heat rising from Earth’s core through the mantle.

• Mantle convection – the slow movement of the mantle due to upwelling and sinking. The circular motion of the mantle as it transports hot material and heat upward, and then transports cooled material downward. The hot material is lower in density, so it rises. The colder material is higher in density and sinks.

Process & Procedure p. 672

• Video Convection & Plate Tectonics• Video Hotspots• Animation Slab Pull

Process & Procedure #6

• If plate motion is driven by mantle convection and upwelling, then plates should be moving __________ from hot spots.

• B. If plate motions is only driven by plates being pulled, then plates should be moving ________ subduction zones.

Process & Procedure #7

• Complete P&P #7 a-e with your partner. Use specific examples in your explanations!

P&P #7

• 7b. About 53 hotspots are shown.• 7c. In general, plates pass over hot spots. There is little, if

any, correclation between hot spots and plate direction. For a relatively small number of hot spots on spreading ridges, the plate moves away from the hot spots (e.g., Iceland, Galapagos, or Afar at the base of the Red Sea). Many more are distributed beneath oceanic plates or continents. Geologic evidence indicates that those hot spots are generally relatively stationary for tens of millions of years (although detailed recent work shows that they can at times drift or migrate through the mantle).

P&P #7

• 7d. Plates move towards subduction zones. For example, the Pacific Plate has a rapid velocity to the northwest toward the Japan and Aleutian trenches. Also, the Australian-Indian Plate is being subducted at the Java Trench, which led to the Andaman-Sumatra earthquake and tsunami in December 2004. Closer to home, the Juan de Fuca Plate is being subducted beneath the Cascadian volcanic arc.

P&P #7

• 7e. From a strict correlation point of view, plate motions do not correlate well with the location of hot spots. Hot spots indicate upwelling and convection in the mantle. This suggests that convection by itself is not a sufficient explanation for plate tectonic motions. Thus, the “pull” of oceanic crust entering subduction zones correlates much better with the direction of plate motions, and the tectonic patterns and landforms on Earth’s surface.

R&C #1 p. 676

• 1a. What part of the world is shown?

• 1b. What tectonic plates are included in the figure?

• 1c. What is the relationship between earthquakes and depth?

• 1d. What kind of tectonic setting is shown by the pattern of earthquakes?

R&C #1 p. 676

• 1e. Sketch in your science notebook where earthquakes occur along this line. What does the depth of the earthquakes indicate?

R&C #2-3 p. 676

• Complete R&C #2 and 3. • Remember to use graph paper for your graph!