Tectonic plates are massive, moving pieces of Earth’s lithosphere Plates ride above circulating, heated rock Geographers study plate movements to understand: - how the earth is reshaped - how earthquakes and volcanoes are formed The largest plates are named after continents: page 37
Plates move in one of four ways: page 38-39 Divergent- by spreading, or moving apart Subduction - diving under another plate Convergent- collision, or crashing together Transform- sliding past each other in a shearing motion
Movement of plates effects surface of the earth Saudi Arabia–Egypt’s plates are spreading apart, widening Red Sea India’s plate is crashing into Asian continent, building up Himalayas
Two plates meeting can cause folding, cracking of rock -Platesmove very slowly - Causes rocks to become more flexible and fold under pressure
Faults occur when pressure causes rock to fracture, or crack. -Sometimes the rock is not flexible and will crack due to plate movement The crack is called a fault Fault line is place where plates move past each other
As the plates move past each other at a fault, the earth shakes or trembles This movement may become violent, called an earthquake
Seismograph -Special device used to detect earthquakes -Measures the size of the waves created by an earthquake
Earthquakes release energy in the form of motion, causing: - landslides - land displacement - fires (broken gas lines) - collapsed buildings Richter Scale — numeric scale showing relative strength of earthquake -Uses info from seismographs to determine the strength of an earthquake -Has no absolute upper limit -Major quake measures a 7 or more
Location in the earth where an earthquake begins is called the focus Epicenter — the point directly above focus on the earth’s surface - In most cases, the epicenter is the area that receives the greatest damage Nearly 95% of earthquakes occur at tectonic plate boundaries
Tsunami, a giant ocean wave, begins at epicenter of an earthquake: - travels at up to 450 mph - waves of 50–100 ft. or higher May travel across wide stretches of the ocean and do damage on distant shores
On March 11, 2011 an 8.9 magnitude earthquake struck Japan. The earthquake and subsequent tsunami has caused vast amounts of damage and the death toll continues to rise. Nearly 16,000 people died as a result.
On December 26th, 2004, an earthquake caused by subduction caused a series of tsunamis along the coasts of the Indian Ocean. Some waves were said to be upwards of 98ft. high. Killing over 230,000 people, the 2004 tsunami is the worst natural disaster in history.
Volcanoes occur where there are cracks in the earth’s surface. Material, such as magma, pours out of the vent. Most volcanoes occur at tectonic plate boundaries
There are several types of eruptions— violent explosions where lava, gases, ash or dust are expelled from the vent in Earth’s crust Lava — magma that has reached the earth’s surface; may create landform
Ring of Fire — zone around rim of Pacific Ocean: - meeting point of eight tectonic plates - vast majority of the earth’s active volcanoes located here
“Hot spots” are where magma rises to surface from mantle Hot springs, geysers indicate high temperatures in earth’s crust Some volcanic action is useful: - volcanic ash produces fertile soil - hot springs are tapped for heat, energy