Geography and Oceanography - Chapter 7 docx

Hotspots, Plumes and Mass Extinctions Is Hawaii more than a great vacation spot?. Plate Tectonics - Distribution of Volcanic and Earthquake Activity... Pacific Hotspot Volcanic Chains...

Hotspots, Plumes and Mass

Extinctions

Is Hawaii more than a great vacation spot?

How does life respond to geologic catastrophes?

Plate Tectonics - Distribution of Volcanic and Earthquake Activity

The Earth’s surface is broken into plates

6

Hawaii

Easter

Galapagos

Samoa

The Hawaiian Hotspot

Volcanoes

to atolls (Darwin)

Tahiti shield volcano

Moorea fringing reef

Raiatea - barrier reef

Bora Bora lagoon

Maupiti the oldest volcanonext stage is the coral atoll

French Polynesia from space

atoll

Pacific Hotspot Volcanic Chains

• Where do Hotspots come from?

• How do Hotspots start?

• How long do they last?

JOIDES Resolution drillship

Reunion hotspot track, central Indian Ocean

“flood” basalts in western India

>300 lava flows, each 1000 km 3

Western

India

• An accumulation

of lava flows 5 km thick!

• Occurred at the same time as the extinction of the dinosaurs

or BOTH?

Impact Site: Yucatan Peninsula

Volcanic catastrophes and Mass

Extinctions

Global Distribution of large, rapidly-erupted volcanic events

Large Igneous Provinces are:

• BIG!!

• NOT explained by Plate Tectonics

• Initial Plume and Hotspot Activity

Mantle Plumes

• Part of the circulation in the Mantle

• Driven by temperature differences

• Hot and cold => density differences

• Gravity Rules!

http://www.youtube.com/watch?v=f37Gf6IVj6o&feature=related

Mantle convection -

the driving force for plate tectonics

What causes the warmer material to rise?

Mantle Plumes

Mantle convection and hotspot formation

Cold lithosphere sinks, hot plumes rise.

Red = hot upwelling from core-mantle

boundary Blue = cold downwelling

Computer Model Cartoon Schematic

Cross-sections of the Earth

Which is not a hotspot?

Iceland

Hawaii

Yellowstone

Mt St Helens

Laki, Iceland (1783) the year without

a summer

Laki, Iceland (1783) the year without

a summer

Submarine: Hydrothermal Exchange –

Release of Metals

Ocean Anoxic Eventsproductivity or preservation?

Marine sedimentary layers exposed

in Italy

Hydrothermal Plumes from LIPs

Effects of Submarine Plateaus

• Release of “reduced” metals uses up

oxygen in the oceans

• Trace metals are “nutrients”, so

promote rapid growth of plankton

• Sinking organic matter also uses up

oxygen in the oceans

• Extinctions of “benthic” marine

organisms

Two Styles of Mantle Convection