HDWK

• Mid Ocean Ridges– Detected a long time ago

• Molten Material (go look! Pillow Lava!)

• Magnetic Stripes

• Drilling Samples

• Subduction and Deep Ocean Trenches

Mid Ocean Ridges

Mid-Atlantic RidgePingvellir, Iceland

• Iceland is ripping apart – but it gets filled in with new lava – so it gets bigger!

Africa is tearing apart too

How Convection helps Sea Floor Spreading (traditional version)

Go Look for Volcanic Activity!

• Pillow lava from the Mid-Atlantic Ridge

• Shows activeeruptions

• Sonar of a volcano & pillows

Magnetic Stripes – Reversals

Drilling the Sea Floor for Rock Ages

Glomar Challenger

• Drilling for Rocks (and used for other things! but we’d have to kill you if

we told you what it was for

)

Can it Spread Forever??

• No Way, It has to go somewhere, and usually it dives under a continent!

• Oceanic Crust is Denser than Continental Crust – so it sinks under the continent.

• This process is called SubductionSubduction and makes the Deep Ocean TrenchesDeep Ocean Trenches

• Subduction and Deep Ocean Trenches

More Detail than you want! Subduction!

Some Vocab• Plate

• Convergent Plate Boundary

• Divergent Plate Boundary

• Transform Plate Boundary

• Sea Floor Spreading

• Magnetic Reversal

• Rift Zone

• Subduction

• Island Arc

Hawaii is Special

• Hawaii is special, it is on the Pacific Plate, but the hotspot under the Big Island appears to have been there for 70+ million years.

• The evidence is the chain of islands stretching out to the NW from Hawaii to Kure – and on along the Emperor Seamount chain.

Kea and Loa

Tectonic Plates - names

• Most of the volcanoes are located on or near ___________________

• _________ volcano is the only one in the middle of a ___________.