GEOL 1 Lecture Notes - Lecture 2: Mid-Ocean Ridge, Oceanic Crust, Divergent Boundary
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Published on 19 Oct 2020
School
Department
Course
Professor
Jeff Koo
Geol 1
Physical Geology
Spring 2019
4 Units
Plates & Plate motion
● Lithosphere: the crust and the uppermost part of the mantle are relatively rigid.
● Asthenosphere: the upper most mantle underlying the lithosphere, is soft and therefore
flows more readily than the underlying mantle. Provides a lubricating layer over which
the lithosphere moves (asthenos means weak)
● Where hot mantle material wells upward it will uplift the lithosphere
● Where the lithosphere is coldest and densest, it will sink down through the asthenosphere
and into the deep mantle.
● Tectonic forces: the effect of this internal heat engine on the crust is of great significance
to geology. The forces generated inside the earth, called tectonic forces, cause
deformation of rock as well as vertical and horizontal movement. Pg. 13
● , divergent, convergent, transform
3 main plate boundaries
● Plates pulling apart (divergent): creation of new ocean floor with submarine volcanoes
oceanic ridge, small to moderate earthquakes
● Plates pulling together (convergent): destruction of ocean floor; creation and growth of
mountain range with volcanos, subduction zone, earth’s greatest earthquakes and
tsunamis
● Plates pulling side by side (transform): no creation or destruction of crust, small to large
earthquakes.
Characteristics of divergent boundaries
-midocean ridges are sites of seafloor spreading pg.492. They have the following characteristics
o -High heat flow
o Seismic wave velocity decreases @ the ridges, due to high temperatures
o A valley is present along the center of ridge
o Volcanoes are present along the ridge
o Earthquakes occur along the ridge
Divergent plate boundaries
● At divergent plate boundaries:
○ Plates move away from each other
■ Can occur in the middle of the ocean or w/ in a continent
■ Divergent motion eventually creates a new ocean basin