EARTH 20 Lecture Notes - Lecture 4: East Pacific Rise, Tonga Trench, San Andreas Fault
Document Summary
Plates are created (mid-ocean ridges)and destroyed (subducted in mantle and ocean trenches) Location of earthquakes and volcanoes & seismic hazards. Equivalent to darwin"s theory of evolution (in biology) in that after its discovery, many seemingly unrelated phenomena came together under a common cause/explanation. Subduction zones = where crust is destroyed. largest earthquakes in the world (m9s) and most violent volcanic eruptions. Long enough to be wrapped around the earth 1. 5 times (60,000 km) 95% of volcanic eruptions take place here (underwater) Plates move apart, magma from asthenosphere rises, cools, solidifies and moves away from the ridge. Mid-ocean ridges (spreading centers): add new crust to edge of lithospheric plates (20 km^3/yr) Despite these changes, earth"s surface remains constant in size (no growth or shrinkage) N and s american are moving away from europe and africa (2-3cm/yr) Melt rises and erupts on ocean floor > cools, solidifies and becomes basaltic rock.
