Natural Disasters and How They Happen

Earthquakes occur when tectonic plates — the massive slabs that make up Earth's outer shell — suddenly slip or grind against each other, releasing enormous energy as seismic waves. There are about 20,000 earthquakes around the world every year.

They are all the same kind of powerful tropical storm, just called different names based on location. In the Atlantic and eastern Pacific they are called hurricanes, in the western Pacific they are typhoons, and in the Indian Ocean they are cyclones.

A tsunami is a series of large, powerful waves most often triggered by an underwater earthquake, though volcanic eruptions or submarine landslides can also cause them. The word tsunami comes from Japanese and means "harbor wave."

The Richter scale, developed by Charles Richter in 1935, measures the magnitude — or size — of earthquakes. Each whole number step up on the scale represents about 31 times more energy released.

The Enhanced Fujita Scale (EF Scale) rates tornado intensity from EF0 (weakest) to EF5 (most violent), based on damage caused. It was updated from the original Fujita Scale in 2007 to better reflect different types of structures and vegetation.

The great San Francisco earthquake of April 18, 1906 measured about 7.9 in magnitude and was followed by devastating fires that burned for three days. It remains one of the deadliest natural disasters in U.S. history, killing an estimated 3,000 people.

The Ring of Fire is a horseshoe-shaped zone encircling the Pacific Ocean where tectonic plates meet. It is home to about 75% of the world's volcanoes and is the site of roughly 90% of the world's earthquakes.

Hurricane Katrina made landfall in August 2005 and caused catastrophic flooding in New Orleans when its levee system failed. The storm caused over 1,800 deaths and more than $125 billion in damage, making it one of the deadliest U.S. hurricanes in a century.

A dormant volcano is one that has not erupted in a very long time — sometimes thousands of years — but still has the potential to erupt again. This is different from an extinct volcano, which scientists believe will never erupt again.

The 2004 Indian Ocean tsunami was caused by a massive 9.1-magnitude earthquake off the northwest coast of Sumatra, Indonesia. The disaster killed approximately 230,000 people across 14 countries and remains one of the deadliest natural disasters ever recorded.

Tornadoes typically form when warm, humid air from the Gulf of Mexico meets cool, dry air from Canada or the Rockies. This clash creates powerful thunderstorms, and under the right conditions, a rotating column of air can descend to the ground as a tornado.

Tornado Alley refers to the broad flat region of the central United States — including Texas, Oklahoma, Kansas, and Nebraska — where the atmospheric conditions are ideal for tornado formation. The flat terrain allows cold Arctic air and warm Gulf air to meet with little natural barrier.

Mount St. Helens erupted on May 18, 1980, in one of the most significant volcanic events in U.S. recorded history. The eruption triggered the largest landslide ever recorded, reduced the mountain's height by about 1,300 feet, and killed 57 people.

A pyroclastic flow is one of the most dangerous volcanic hazards — a superheated avalanche of gas, ash, and rock that can travel at speeds up to 450 miles per hour at temperatures exceeding 1,000 degrees Fahrenheit. The ancient Roman city of Pompeii was destroyed by a pyroclastic flow from Mount Vesuvius in 79 AD.

A hurricane watch means dangerous conditions are possible within the next 48 hours, giving people time to prepare or evacuate. A hurricane warning means those dangerous conditions — including sustained winds of 74 mph or higher — are expected within 36 hours, signaling that final preparations must be completed immediately.