10.3 Volcanoes and Earthquakes Flashcards
What are Volcanoes?
-Volcanoes form where extremely hot, magma accumulates below weak spots in the Earth’s crust
-During a volcanic eruption, magma is pushed to the surface with great force. Gas, ash and solid rock is also often released.
-Once magma reaches the surface, it is called lava. Lava can reach ~1200C
-Lava cools and solidifies to form new rock.
What are Volcanoes at Divergent Plate Boundaries?
-Create weaknesses in the crust as separating plates thin the crust, allowing magma to find its way up
-Most volcanoes can be found at plate boundaries
What are Volcanoes at Convergent Plate Boundaries?
-create weak spots as the subducting plate melts, magma rises to form volcanoes
What are Hot Spots Volcanoes?
-Hot spots are isolated weak points in the crust that are away from a plate boundary
-creates a volcano or volcanic island directly above it
-As the tectonic plate moves across the hot spot, new volcanoes form, leaving a chain of islands behind it
-One such island chain is the Hawaiian Islands.
Hawaii is the current island above the hotspot, it’s volcano is active
What are Earthquakes?
-Tectonic plates are typically held together with friction
-When other forces overcome the friction forces, the plates slip, releasing waves of energy into the rock or water around it
-Earthquakes most commonly occur at plate boundaries, especially convergent boundaries
What are the 3 Types of Waves?
-Primary waves (P-waves) move longitudinally (back and forth) that travel fast
-Secondary waves (S-waves) move transversely (up and down) and travel slower than P-waves
-Surface waves move in a rolling motion and are the slowest. They cause the most destruction
How do Earthquakes Occur?
-Earthquakes happen at specific points where the earth slips, usually along fault line
-The location where the quake starts is called the focus (this may be hundreds of kilometers underground)
-The location directly above the focus at ground level is called the epicenter
How to Detect Earthquakes?
-Seismometer: A weighted pencil on a drum, the paper drum would move with the quake while the pencil stayed stationary due to the weight.
-Chinese seismometer:
Dragons held balls in their mouth, if the ball dropped into the frog, it predicted an earthquake in that direction.
How is Earthquakes’ Severity Measured?
-Richter scale.
-A logarithmic scale: each number represents a 10-fold increase, each fold is 10 times severer than the previous one
What is the Tectonic History of Australia?
-The lithosphere under Australia is 200km thick – thicker than most other continents.
The continent is does not sit on a plate boundary prevents continental rock from being destroyed
