Volcanoes and Earthquakes 2023 PDF

VOLCANOES AND EARTHQUAKES CHAPTER 10.3 VOLCANOES  Volcanoes form where extremely hot, molten rock (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 m...

VOLCANOES AND EARTHQUAKES CHAPTER 10.3 VOLCANOES  Volcanoes form where extremely hot, molten rock (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 ~1200oC!  Lava cools and solidifies to form new rock. VOLCANOES AT PLATE BOUNDARIES  Plate boundaries are where the Earth’s crust is the thinnest / weakest.  Divergent plate boundaries create weaknesses in the crust as separating plates thin the crust, allowing magma to find its way up. VOLCANOES AT PLATE BOUNDARIES  Convergent boundaries also create weak spots – as the subducting plate melts, magma rises to form volcanoes  VOLCANOES AND PLATE BOUNDARIES  Hence, most volcanoes can be found at plate boundaries e.g. Pacific Ring of Fire.  HOT SPOT VOLCANOES  Hot spots are isolated weak points in the crust that are away from a plate boundary.  Scientists are still not sure why hot spots exist.  The hot spot creates a volcano / volcanic island directly above it.  As the tectonic plate moves across the hot spot, new One such island chain is the Hawaiian Islands. volcanoes form, leaving a chain Hawaii is the current island above the hotspot  of islands behind it. it’s volcano is active. VOLCANOES SUMMARY Plate Boundary Volcanoes Hot Spot Volcanoes  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  DETECTING EARTHQUAKES  These waves of energy are called seismic waves. There are 3 types:  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.  WHERE EARTHQUAKES OCCUR  Earthquakes most commonly occur at plate boundaries – especially convergent boundaries  EARTHQUAKES: FOCUS VS EPICENTER  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.  DETECTING EARTHQUAKES  Earthquakes are measured using a seismometer.  Earlier seismometers:  A weighted pencil on a drum – the paper drum would move with the quake while the pencil stayed stationary due to the weight.  DETECTING EARTHQUAKES  Chinese seismometer:  Dragons held balls in their mouth – if the ball dropped into the frog, it predicted an earthquake in that direction. RICHTER SCALE  Earthquakes severity is measured using the Richter scale.  A logarithmic scale: each number represents a 10-fold increase (a magnitude 5.0 earthquake is 10 times more destructive than a magnitude 4.0).  TECTONIC HISTORY OF AUSTRALIA  The Australian continent is unique and old due to:  The lithosphere under Australia is 200km thick – thicker than most other continents.  The continent is does not sit on a plate boundary.  This prevents continental rock from being destroyed. Some of this rock has been used to infer the geological history of Australia as it drifted apart from being part of Pangea. EARTHQUAKES SUMMARY