Earthquakes and Volcanoes

• Earthquakes and Volcanoes are natural phenomena with specific causes

Earthquakes

• Earthquakes are vibrations in the Earth's ground and caused by the movement of plates at fault lines

Faults

• Faults are breaks in Earth's lithosphere where blocks of rock move
• Strike Slip Fault occurs at transform plate boundaries
• Normal Fault occurs at divergent plate boundaries
• Reverse Fault occurs at convergent plate boundaries

Earthquake Terminology

• Seismic Waves are energy that travels as vibrations within the Earth
• Focus is the point inside the Earth where an earthquake begins
• Epicenter is the location on the Earth's surface directly above the focus

Types of Seismic Waves

• Primary Waves (P-waves) travel in a push-pull motion, and are the fastest-moving seismic waves that can travel through solids and liquids
• Secondary Waves (S-waves) are slower than P-waves and can only travel through solids
• Surface Waves move in a rolling motion, are the slowest seismic waves, and cause the most damage at the Earth's surface
• The Earth's outer core is liquid.

Finding an Epicenter

• Triangulation helps scientists find an earthquake's epicenter
• Locate the difference between the arrival time of the P-wave and the arrival time of the S-wave
• Using an earthquake distance graph, determine the distance from the epicenter
• Draw a circle with the given distance around the seismograph station, repeat for two more stations
• The point where the circles intersect indicates the epicenter

Measuring Earthquakes

• The Richter Scale measures the amount of ground motion at a given distance to measure the intensity of earthquakes
• The Moment Magnitude Scale measures the total energy released by an earthquake
• The Modified Mercalli Scale measures the intensity of an earthquake based on the amount of damage, rated on a scale of I to XII

Earthquake Risks

• Seismologists use five indicators to assess earthquake risk: past earthquakes, probability, population density, geology around a fault, and building design

Volcanoes

• A volcano is a vent in Earth's crust through which molten rock flows
• Volcanoes form at convergent plate boundaries where one plate subducts under another
• Volcanoes form at divergent boundaries when two plates separate and magma rises
• Volcanoes form at hot spots, not associated with plate boundaries, and can form chains of islands like Hawaii

Types of Volcanoes

• Shield Volcanoes are large, shield-shaped with gentle slopes and eruptions
• Composite Volcanoes are large, steep-sided volcanoes that result from explosive eruptions
• Cinder Cone Volcanoes are small, steep-sided volcanoes that erupt gas-rich, and basaltic lavas

Terminology

• A caldera is a large volcanic depression created when the summit of a volcano collapses during a violent eruption

Types of Volcanic Eruptions

• Violent eruptions feature lava with high viscosity and gas content
• Quiet eruptions feature lava with low viscosity and gas content

Effects of Volcanic Eruptions

• Lava flows move slowly, can destroy towns, and are rarely deadly
• Ash fall can cause breathing problems and disrupt air traffic, and can cool Earth's atmosphere
• Mudflows can occur when snow and ice melt and mix with mud or ash
• Pyroclastic flows are often deadly, occur from violent eruptions, and release gas, ash, and rock into the air

Predicting Volcanoes

• Ground deformation, an increase in earthquakes, an increases in volcanic gasses, and more acidic water near a volcano can all be used to help predict volcanic eruptions

Climate

• Volcanic eruptions affect climate
• Volcanic ash blocks the sun, which causes a decrease in global temperatures
• Volcanic eruptions can also cause acid rain