Transcript 11 Sea Floor

Geology 12
Presents

Unit Outline
– Chp 10 Earth’s
Interior
– Chp 11 Sea Floor
– Chp 12 Plate
Tectonics
– Chp 9 Seismic (EQ)
– Chp 13 Structure
Chp 11 Seafloor
• Volcanoes outgasses water to fill oceans
• Average depth = 4 km
• Continental Margins mark edge of
continent from deep sea floor
– 2 types of margins
1. Passive Margin = where oceanic plate is
fused to continental plate and large
amount of sediment is deposited.
– Ex: Eastern N. America
Cont’l Margin
Cont’l Shelf
Abyssal
Plain
Submarine
canyon
Oceanic Plate
Cont’l Plate
fused
• Submarine canyons
– Cut into cont’l shelf-slope by:
• a) rivers when sea-level was up to 130
m lower during ice ages
• animation
• b) turbidity currents = underwater
landslides that erode slope and travel
for 100’s of km
– Sediments are deposited as a deep sea
fan as graded bedding
Passive Margins
New York
Hudson River Submarine Canyon
2. Active Margin = where oceanic plate is
subducting under continental plate
Ex: W. coast of S. America
Cont’l shelf
Cont’l slope
Trench
Volcano
Abyssal plain
Cont’l plate
Oceanic plate
Active Margins
• Oceanic (spreading) Ridge: where new
oceanic plate is being created by
volcanism
Island/seamount
seamounts
Rift valley
peridotite
mantle
Ocean Ridge
• Guyots
New volcanic
island
Eroded flat by
waves
Guyot
Guyots & Seamounts
Guyots & Seamounts
• Reefs
Top view
lagoon
Cross
section
Fringing
reef
Barrier
reef
Atoll
Fringing Reef Island
Barrier Reef Island
Atoll
• Islands get smaller as they age due to:
– a) wave erosion
– b) oceanic plate sinks as it moves way from
divergent boundary or hot spot
– See Q14d, p.9 of WS 12.2
Use the diagram of a typical ocean basin to answer question 6.
6. The diagram represents a cross-section of an ocean
basin. The number which represents a diverging plate
boundary is
A. 1
B. 2
C. 3
D. 4
Read Chapter 11
Do WS 11.1
Read Chapter 12
Go to Chp 12 Plate Tectonics