Download Lecture 11A / The Ocean Floor

The Sea Floor
GLG 101 - Physical Geology
Bob Leighty
These notes and web links are your primary “lecture” content in this class.
Additionally, various articles are assigned each week to supplement this “lecture”
information. I believe you’ll have enough information to reference without having
to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes.
You’ll find they are loaded with imagery and streamlined text that highlight the
most essential terms and concepts. The notes provide a framework for learning
and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have
included numerous hyperlinks to external web sites (like the Wikipedia, USGS,
NASA, etc.). Follow the links and scan them for relevant info. The information
from linked web sites is meant to supplement and reinforce the lecture notes –
you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content
more independently than in a traditional class. As always, I will help guide you
through this learning adventure. Remember, email Dr. Bob if you have any
questions about today’s lecture ([email protected]).
Leave no questions behind!
Explore and have fun!
Sea Floor
The Sea Floor
 Much of Earth’s surface is underlain by oceanic crust
 Oceans include >97% of all water on Earth
 Earth's early history - volcanic “outgassing” & asteroids/comets
Sea Floor
Mapping
 Mapped mainly by sonar & satellite radar since WWII
Sea Floor
Oceanic Sediment
 Derived from land (terrigenous) – mud & sand
 Derived from critters (biogenic) – chert & limestone
Sea Floor
Continental Margins
Passive
 Minimal tectonism; no oceanic trench or volcanic arc
 Example - east coast of N & S America, west coast of Africa
Sea Floor
Continental Margins
Passive
Continental Shelf
 Shallow water (<135 m deep); affected by waves
 Gently-sloping; underlain by continental crust
Sea Floor
Continental Margins
Passive
Continental Shelf
Sea Floor
Continental Margins
Passive
Continental Slope
 Deeper water (>135 m); not affected by waves
 Steeper than the shelf; submarine canyons
Sea Floor
Continental Margins
Passive
Continental Rise
 Very deep water; grades into the abyssal plain of the deep ocean
 Gently-sloping; underlain by oceanic crust
Sea Floor
Continental Margins
Active
 Lots of tectonism; develop at subduction zones
 Example - west coast of N & S America
Sea Floor
Continental Margins
Turbidity Currents
 Dense, “muddy” underwater currents
Sea Floor
Deep Ocean Basins
Abyssal Plains
 Deep ocean (avg ~5000 m)
 Flattest places on Earth (deep-sea
sediment covers & subdues topography)
Sea Floor
Deep Ocean Basins
Oceanic trenches
 Deepest parts of the ocean (some >10,000 m)
 Develop at subduction zones, parallel to volcanic arcs
Sea Floor
Deep Ocean Basins
“Hot spots”
 Volcanic mountains that form above mantle plumes
 Example: Hawaiian Island-Emperor Seamount chain
Sea Floor
Deep Ocean Basins
Seamounts
 Isolated volcanic peaks that may rise above sea level
 Guyots = old, high seamounts eroded flat
Sea Floor
Deep Ocean Basins
Coral Reefs & Atolls
 Organisms typically prefer warm, clear, shallow water
Sea Floor
Deep Ocean Basins
Mid-ocean Ridges
 Divergent plate boundaries (spreading centers)
Sea Floor
Deep Ocean Basins
Mid-ocean Ridges
 Total >70,000 km long!
Sea Floor
Deep Ocean Basins
Mid-ocean Ridges
 Rise 2-3 km above ocean basins
Sea Floor
Deep Ocean Basins
Mid-ocean Ridges
 Mostly mafic rocks (basalt & gabbro);
pillow lavas
 Normal faults & transform faults
Sea Floor
Deep Ocean Basins
Mid-ocean Ridges
 Black smokers & “weird” critters
Tube worms
Black smokers
Sea Floor
WWW Links in this Lecture
> Oceanic crust - http://en.wikipedia.org/wiki/Oceanic_crust
> Oceanic trench - http://en.wikipedia.org/wiki/Oceanic_trench
> Volcanic arc - http://en.wikipedia.org/wiki/Volcanic_arc
> Continental crust - http://en.wikipedia.org/wiki/Continental_crust
> Continental shelf - http://en.wikipedia.org/wiki/Continental_shelf
> Submarine canyon - http://en.wikipedia.org/wiki/Submarine_canyon
> Shelf-slope break - http://en.wikipedia.org/wiki/Continental_shelf#Continental_shelf_break.2C_slope.2C_and_rise
> Abyssal plain - http://en.wikipedia.org/wiki/Abyssal_plain
> Subduction zone - http://en.wikipedia.org/wiki/Subduction
> Hot spot - http://en.wikipedia.org/wiki/Hotspot_%28geology%29
> Mantle plume - http://en.wikipedia.org/wiki/Mantle_plume
> Hawaii-Emperor seamount chain - http://en.wikipedia.org/wiki/Hawaiian-Emperor_seamount_chain
> Seamount - http://en.wikipedia.org/wiki/Seamount
> Guyout - http://en.wikipedia.org/wiki/Guyot
> Atoll - http://en.wikipedia.org/wiki/Atolls
> Mid-ocean ridges - http://en.wikipedia.org/wiki/Mid-ocean_ridges
> Pillow lava - http://en.wikipedia.org/wiki/Pillow_lava#Pillow_lava
> Black smoker - http://en.wikipedia.org/wiki/Black_smokers