Lecture 4 Flashcards

Made for Quarterly Test #1

True North

Fixed point on the Earth where all lines longitude intersect

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Also called rotational axis

Magnetic North

Aligned with Earth’s magnetic field, and changes with time

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It is what a compass needle points to

Wilson Cycle

Model of plate tectonics that shows the life cycle of ocean basins

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(Formation, growth, destruction)

Mantle Convection

Very slow motion of Earth’s solid mantle caused by currents moving heat

What makes plates move?

Mantle convections and heat sources

Heat sources that make plates move

Major: Decay of radioactive isotopes

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Minor: Earth’s core

Ridge Push

Mid-ocean is at a higher elevation

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As new crust is added, it pushes the old crust down the slope

Slab Pull

Subducting crust is more dense than overlying crust

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Old crust sinks down into the mantle

Topography

Elevation above mean sea level

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Used to quantify and describe the shape of land features

Bathymetry

Depth below mean sea level

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Used to quantify and describe the shape of sea floor features

Puller Sounding Machine

Way of bathymetry

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Long line with a weight at the end, gives one measurement for each spot tested

Contours

Separate values, high on one side of line and low on the other

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Elevation = topographic contours

Depth = bathymetric contours

Thickness = isopachs

Echo Sounder

Sends a sound signal (ping) from the ship downward into the ocean

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Sound hits seafloor, produces echo, which returns to ship

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Speed of sound determines average sea depth

Multibeam echo sounders

Map seafloor in very detailed strips with multiple soundwaves

Earth Orbiting Satellites

Sea floor features exert a gravitational pull that can be measured by dips in the water surface

Seismic Data for Sea Floor

Sound shot into the subsurface

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Sound waves are reflected off different rock layers

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Produces an image of the subsurface

Hotspots

A volcano within a tectonic plate

Mantle Plume

Column of molten rock of hot aqueous fluid in one place for a long time

Yellowstone Caldera

Hotspot track within the North American tectonic plate, rare

Seamounts and Tablemounts

Volcanoes formed on the ocean floor forming over hotspot or at mid-ocean ridge much higher than the surrounding ocean floor

Seamount

Cone-shaped underwater volcano

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May or may not rise above sea level

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May become a tablemount if above sea-level and subject to elements or erosion

Tablemount

Flat-topped underwater volcano