Lecture 16 Flashcards
How much do plates move in a year?
Plates moves an average of about 4 cm/year.
What is the energy source that drives this motion?
Comes from the Earth’s interior - geothermal energy. The source of geothermal energy is from radioactive decay and residual heat from Earth’s formation.
Radioactive Decay
Arises from the spontaneous decomposition of unstable isotopes of potassium, uranium, and thorium contained within the solid Earth. NOT a permanent energy source!
Residual Heat
Related to heat produced in Earth’s interior when Earth was first created.
Volcanoes
Volcanic eruption brings magma to the surface to form “extrusive” igneous rock.
2 types of classification schemes for volcanoes
Eruptive history (active, dormant, extinct) and topographic form (shield volcanoes, stratovolcanoes, cinder cones, and basalt plateaus)
Shield Volcanoes
rounded and low profile. Formed from successive lava flows. Typically of basaltic composition. Usually not explosive.
Stratovolcanoes
Builty by successive layers of lava of andesitic composition. More explosive than shield.
Mountain Ranges
Most mountain building (or orogeny) is currently occuring along convergent plate boundaries.
Islands
Often find shield volcanoes along ocean-ocean convergent plate boundaries. This produces island arcs.
Hotspots
Hypothesized that at specific places in the asthenosphere, a fountain of hot lava is continuously flowing toward the surface. The repetition of this process over millions of years leaves trail of volcanic islands and seamounts.
Craton
Stable interior of ancient rock (~billions of years old)
The shield
The portion of the craton that is not covered by sedimentary deposits.
Late Cambrian
~500 MYA. 6 major continents: mostly in the tropical latitudes.
Silurian
408-438 MYA
