Lecture 4 Flashcards

Made for Quarterly Test #1

True North

Fixed point on the Earth where all lines longitude intersect

Also called rotational axis

Magnetic North

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

It is what a compass needle points to

Wilson Cycle

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

(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

Minor: Earth’s core

Ridge Push

Mid-ocean is at a higher elevation

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

Slab Pull

Subducting crust is more dense than overlying crust

Old crust sinks down into the mantle

Topography

Elevation above mean sea level

Used to quantify and describe the shape of land features

Bathymetry

Depth below mean sea level

Used to quantify and describe the shape of sea floor features

Puller Sounding Machine

Way of bathymetry

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

Elevation = topographic contours

Depth = bathymetric contours

Thickness = isopachs

Echo Sounder

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

Sound hits seafloor, produces echo, which returns to ship

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

Sound waves are reflected off different rock layers

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

May or may not rise above sea level

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

Tablemount

Flat-topped underwater volcano