Other Important Processes on Earth
This term applies to all land forming activities associated with molten, igneous rocks by the cooling of magma (molten materials). As a magma chamber intrudes into the crust and rises toward the surface, it cools and crystallizes. Vulcanism today occurs at lithospheric plate boundaries (spreading centers and subduction zones) and hot spots. Important examples include:
- Basaltic volcanism : occurs in association with sea-floor spreading centers
and oceanic hot spots.
Pillow Lava is formed in this way (movie).
- Shield volcano : magma rises to the surface from asthenosphere along cracks and
large fissures, can flow outward over long distances before solidifying and forms a broad,
gently sloping volcano. The Hawaiian
islands are an example. Shield volcanoes represent the accumulation of thousands of
eruptions, built up over many thousands of years.
- Flood basalts : many breaks in the crust allow magma to pour out all over, forming vast areas (10,000s of sq. mi.) covered by horizontal beds of lava. These create extensive lava plateaus, like those that form the Columbia Plateau in Oregon/Washington/Idaho.
Erosion and Deposition
Erosion, either physical (weather) or chemical, loosens and removes surface and soil
materials (regolith or sediment production). Sediment transport and deposition, carries
sediments away from their source area and redeposits them elsewhere.
Earth's Magnetic Field
Paleomagnetic records indicate that the geomagnetic field has
existed for at least three billion yrs. Based on the size
and electrical conductivity of the Earth's core, the field
would decay away in only about 20,000 years. Also, the dipole polarity has
reversed many times in the past (see previous page of notes!).
A mechanism within the Earth's interior must continually generate the geomagnetic field. Geologists believe that the liquid iron in the outer core is slowly convecting, and that these motions set up electric currents in the metal. This mechanism is called a convective dynamo.