Physical Geology 101
Seafloor Spreading

Seafloor Spreading

Harry Hess, 1962 - proposed theory of Seafloor Spreading
New ocean floor crust is created at mid-ocean ridges, which are created by upwelling mantle material. Oceanic crust is then carried away from ridges and eventually sinks back into Earth's interior at deep sea trenches.
Evidence supporting this theory?

Ocean Floor

Prior to WWII, very little was known about the ocean bottom - features, its composition, topography
Use of the fathometer on naval vessels and greater use of submarines began to change this.

Collecting the Data

Harry Hess ran his fathometer continuously across the oceans, gathering data
The ocean bottom contained three important features.
Explaining the formation of these features pointed at seafloor spreading.

Mid-Ocean Ridges

Long, linear elevated areas of seafloor.
Often, but not always, with a narrow valley running along the crest of the ridge.


Guyots are flat-topped seamounts
Guyots have had the top of the cone chopped off by wave erosion.
Wave erosion quickly chops off the top of volcano, forming a guyot.

Deep Sea Trenches

Narrow, linear zones on the ocean floor that are trough-like depression.

Putting it All Together

How do mid-ocean ridges, guyots and deep sea trenches come together to form the basis of seafloor spreading?
"Geo-poetry"? What did Harry Hess mean when he called his own theory of Seafloor Spreading "Geo-poetry"?

Continental Drift

What is the importance of the theory of Seafloor Spreading?