Convection currents in the mantle drive plate movement! Hot magma rises, cools, and sinks, creating a convection cell. This drags the plates along. The heat comes from the core (about 5,000°C) and radioactive decay of elements (uranium, thorium, potassium). The theory of plate tectonics was developed in the 1960s, combining continental drift (Alfred Wegener, 1912) and seafloor spreading (Harry Hess, 1960s). The plates interact at plate boundaries: divergent (spreading apart), convergent (coming together), and transform (sliding past). The Pacific Plate is the largest. The "Ring of Fire" (Pacific Ocean) is where many earthquakes and volcanoes occur. So the correct answer is convection currents in the mantle.

The Richter scale measures magnitude! It was developed by Charles Richter in 1935. The moment magnitude scale (Mw) is now used for large earthquakes. The Modified Mercalli scale measures intensity (observed effects). Earthquakes are caused by tectonic plate movement (convergent, divergent, transform boundaries). The San Andreas Fault in California is a transform boundary. Aftershocks are smaller earthquakes that follow the main shock. The largest recorded earthquake was the 1960 Valdivia earthquake in Chile (magnitude 9.5). The 2011 Tohoku earthquake (magnitude 9.0) triggered a tsunami and the Fukushima nuclear disaster. Earthquake early warning systems (ShakeAlert) provide seconds to minutes of warning. Building codes (seismic retrofitting) reduce damage. So the Richter scale is the answer.

Divergent boundaries form the Mid-Atlantic Ridge! Convergent boundaries (subduction) form the Andes Mountains, the Himalayas (continent-continent collision), and the Mariana Trench. Transform boundaries (San Andreas Fault) cause earthquakes. Divergent boundaries can also form rift valleys (East African Rift Valley). The Red Sea is forming at a divergent boundary (Arabian and African plates are separating). So the answer is divergent boundary.

Magma is underground; lava is above ground! Magma forms in the mantle (about 50-200 km deep). When it erupts, it is called lava. Lava can be basaltic (low viscosity, flows easily), andesitic (intermediate), or rhyolitic (high viscosity, explosive). Shield volcanoes (Hawaii) have gentle slopes; stratovolcanoes (Mount Fuji, Mount St. Helens) are steep and explosive. Calderas form when a volcano collapses after a major eruption. The Ring of Fire has many volcanoes. Volcanoes can also be found at hotspots (Hawaii, Yellowstone). The Volcanic Explosivity Index (VEI) measures eruption size. The largest eruption in recorded history was Mount Tambora (1815, VEI 7), which caused the "year without a summer." So magma is underground; lava is above ground.

P-waves (primary waves) travel the fastest! They arrive first at seismographs. S-waves (secondary waves) arrive second. Surface waves are the slowest but cause the most damage. P-waves can travel through solids, liquids, and gases. S-waves cannot travel through liquids (which is how we know the outer core is liquid). Seismologists use the arrival times of P- and S-waves to locate the epicenter. The Richter scale measures amplitude; the moment magnitude scale measures energy. Seismographs record ground motion. The study of seismic waves has helped us map the Earth's interior (crust, mantle, outer core, inner core). So P-waves are the fastest.

Underwater earthquakes cause most tsunamis! The 2004 Indian Ocean earthquake (magnitude 9.1-9.3) triggered a tsunami that killed over 200,000 people in 14 countries. The 2011 Tohoku earthquake (magnitude 9.0) triggered a tsunami that caused the Fukushima nuclear disaster. Tsunami warning systems use seismic data and ocean buoys (DART). If you feel a strong earthquake near the coast, move to higher ground immediately. A tsunami can arrive within minutes. Tsunamis are not tidal waves. So the answer is underwater earthquakes.

The Ring of Fire is a zone of intense tectonic activity! It includes the Andes, the Rockies, Japan, Indonesia, and New Zealand. The Pacific Plate is subducting under many other plates. This causes magma to rise, creating volcanoes. Earthquakes occur as the plates grind past each other. The Ring of Fire has about 75% of the world's active volcanoes and 90% of earthquakes. Famous volcanoes: Mount St. Helens (USA), Mount Fuji (Japan), Krakatoa (Indonesia). The Ring of Fire is a product of plate tectonics. So the answer is that it is located along plate boundaries.

Pyroclastic flows are deadly! They are produced by explosive eruptions. The gas can be superheated (1,000°C). The flow moves downhill due to gravity. It can travel many kilometers. The eruption of Mount Pelée (1902) destroyed the city of Saint-Pierre, killing about 30,000 people. Only two people survived (one was a prisoner in a dungeon). Pyroclastic flows also occurred at Mount St. Helens (1980) and Mount Vesuvius (79 CE, destroying Pompeii). They are associated with stratovolcanoes. So a pyroclastic flow is a hot, fast-moving cloud of ash and gas. It is extremely dangerous. So the answer is a fast-moving current of hot gas and volcanic matter.

GPS measures ground deformation! Tiltmeters measure the angle of the slope. Seismometers detect volcanic earthquakes (harmonic tremor). Gas sensors (sulfur dioxide, carbon dioxide) increase before eruptions. Thermal cameras detect hot spots. Scientists can often predict eruptions weeks to months in advance, but not always. The 1980 eruption of Mount St. Helens was predicted. The 1991 eruption of Pinatubo was also predicted, saving thousands of lives. However, some eruptions occur with little warning (e.g., 1994 eruption of Rabaul, Papua New Guinea). Predicting volcanoes is difficult but improving. So GPS is used to measure ground deformation. The correct answer is GPS.

Drop, Cover, and Hold On is the correct answer! Do not run outside (falling debris). If you are in bed, stay there and cover your head with a pillow. If you are driving, pull over to a clear spot and stay in the car. Do not use elevators. After the shaking stops, check for injuries and gas leaks. Expect aftershocks. Prepare an emergency kit (water, food, flashlight, first aid). Practice earthquake drills. The "triangle of life" method (getting next to furniture) is not recommended. So the correct answer is Drop, Cover, and Hold On.