Earthquakes and Volcanoes

• Earthquakes and volcanoes are caused by specific geological activities.

Earthquakes

• Earthquakes are vibrations in the Earth's ground caused by the movement of plates at fault lines.
• Most earthquakes occur along plate boundaries.
• A fault is a break in Earth's lithosphere where one block of rock moves toward, away from, or past another block of rock.
• Strike-slip faults occur at transform plate boundaries.
• Normal faults occur at divergent plate boundaries.
• Reverse faults occur at convergent plate boundaries.
• Seismic waves are energy that travels as vibrations on and in Earth.
• The focus is a point inside Earth where the earthquake first starts.
• The epicenter is the location on Earth's surface directly above the focus.
• Primary waves (P-waves) travel in a push-pull motion through solids and liquids, and are the fastest moving seismic waves.
• Secondary waves (S-waves) are slower than P-waves, travel only through solids.
• Scientists discovered that the Earth's outer core is liquid because S-waves cannot travel through liquids, but P-waves can.
• Finding the epicenter of the triangulation involves a 4-step process.
• First, the difference between the arrival time of the P-wave and the S-wave(lag time) must be found.
• Followed by using an earthquake distance graph to determine the distance from the epicenter.
• Next, draw a circle with the correct distance around the station and repeat for two more stations.
• The point where the circles intersect is the epicenter.
• The Richter Scale measures the amount of ground motion at a given distance.
• 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, using a scale from I to XII.
• Seismologists use 5 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 boundaries where one plate subducts under another.
• Volcanoes form at divergent boundaries where two plates separate and magma comes out.
• Volcanoes form at hotspots, which are not associated with plate boundaries.
• Hotspot volcanoes usually form chains of islands, such as Hawaii.
• Shield volcanoes are large, shield-shaped volcanoes with gentle slopes and gentle 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, basaltic lavas which causes moderately explosive eruptions.
• A caldera is a large volcanic depression created when the summit of a volcano collapses during a violent eruption.
• Violent eruptions have lava with a high viscosity and gas content.
• Quiet eruptions have lava with a low viscosity and gas content.
• Lava flows move slowly, can destroy towns, and are rarely deadly.
• Ash fall can cause breathing problems, cool Earth's atmosphere, and disrupt air traffic.
• Mudflows can occur when snow and ice melt and mix with mud/ash.
• Pyroclastic flows are produced from violent eruptions that throw gas, ash, and rock into the air, posing a deadly threat.
• Ground deformation, increase in earthquakes, increased volcanic gas, and more acidic water near the volcano can be used to predict volcanoes.
• Volcanic ash blocks the sun, causing a decrease in global temperatures.
• Volcanic eruptions can also cause acid rain.

Explore the causes and effects of earthquakes and volcanoes. This includes understanding plate tectonics, faults (strike-slip, normal, and reverse), and seismic waves (P-waves and S-waves). Learn about the focus and epicenter of earthquakes.