Download Seafloor spreading

Seafloor
spreading
What is a mid ocean
ridge?
• A mid-ocean ridge is an
underwater mountain
system formed by plate
tectonics. It consists of
various mountains linked in
chains
What do mid-ocean
ridges do?
• Harry Hess proposed that at mid-ocean
ridges, magma flows up from the mantle
and forms new crust on both sides of the
ridge
• This new crust makes the ocean floor wider
and pushes the continents surrounding it
farther away from each other.
• Drilling of the seafloor confirmed that
oceans are youngest along mid-ocean
ridges and oldest along their edges.
• When oceanic crust and continental crust collide,
the thinner yet denser oceanic crust dives below
the thicker & lighter continental crust forming a
deep trench.
• What is a trench?
• Trenches form when one tectonic plate slides
beneath another plate at a subduction zone.
• As the oceanic crust sinks into the mantle, it melts
and the recycling process begins.
• As a result, volcanic mountain ranges form along
the continental crust, and earthquakes are
common in the area.
Monday Oct. 17
• Discussion:
o What did you observe about the mid-ocean ridge system?
o What do you think causes the ridge system?
o What other features did you observe when you zoomed in for a closer
look? These are transform faults, which connect segments of mid-ocean
ridges, and fracture zones, which are indicated by offsets in the ocean
crust resulting in a deep canyon.
o What did you observe near the continents?Trenches.
Thursday Oct. 20
• Pre-Activity Discussion
• 1. Where would we find the youngest rocks in the
ocean floor? Along the mid-ocean ridges.
• 2. Where would we find the oldest rocks in the
ocean floor? Near the trenches.
• 3. How do the rocks get from the ridges to the
trenches? The magma welling up from Earths hot
interior pushes the older rock toward the trenches.