Andrew Hollandbeck

An earthquake is the sometimes violent shaking of the ground caused by movements of Earth's tectonic plates. Most earthquakes occur along fault lines, which is where two tectonic plates come together. ©Andrey VP / Adobe StockEarthquakes strike suddenly and violently and can occur at any time, day or night, throughout the year.

Many people mistakenly believe that Cinco de Mayo is Mexican Independence Day. That simply isn't true; Cinco de Mayo celebrates an event that happened in the city of Puebla more than 50 years after Mexico won independence from Spain — and Spain doesn't even figure into Cinco de Mayo. ©Artefacti / Adobe Stock The history of Cinco de Mayo In 1861, Mexican President Benito Juárez stopped making interest payments to Mexico's creditors.

Mother's Day as a national holiday in the United States is almost a century old, but its roots go back before the Civil War to a hard-working Virginian mother and activist named Anna Reeves Jarvis. ©Akarawut / Adobe StockIn total, Anna Reeves Jarvis gave birth to 11 children, though only four of them survived to adulthood.

To most Americans, the flag of the United States of America is more than just a piece of cloth. The Stars and Stripes represents American freedom, democracy, and sacrifice and should be treated with respect. Respect can mean different things to different people, but the U.S. government isn't going to let individual whims dictate how the flag should be handled.

Father's Day, celebrated in the United States on the third Sunday of June, got a jump start from the formation of Mother's Day. Credit for beginning Father's Day celebrations is given to Sonora Smart Dodd (1882—1978) of Spokane, Washington. ©MarijaBazarova / Adobe StockAt the turn of the century, Mother's Day observances were growing across the United States.

Bastille Day, formally called La Fête Nationale ("The National Celebration"), is celebrated every July 14 in France to commemorate the storming of the Bastille, a fortress-prison. Like the July 4 Independence Day in the United States, Bastille Day memorializes the start of a political revolution aimed at replacing an absolute monarchy with a constitutional government.

Labor Day, observed on the first Monday in September in the United States, is considered by many to mark the end of summer. Although it is ostensibly meant to celebrate the civic and economic contributions of American workers, it is also connected historically to workers' repression and political appeasement. Exactly who first came up with the idea of Labor Day is unclear, but two stories are at the front of the running: In the first story, Peter McGuire, cofounder of the American Federation of Labor (AFL) and general secretary of the Brotherhood of Carpenters and Joiners, first suggesting a Labor Day holiday to honor those whose sweat and toil created the country's prosperity.

A hailstone begins life as a core of ice crystals or frozen water. Warm, moist air from underneath a storm cloud creates a strong updraft so that, instead of falling to the earth, that core is blown up through the moist storm cloud, collecting layers of ice — a process called accretion. As the warm updraft cools, it loses its energy and gravity takes hold of the hailstone, pulling it back down through the storm cloud and collecting still more layers of ice.

A tsunami is a series of ocean waves caused by a sudden displacement of water. Tsunamis are most often caused by earthquakes, but they can also be caused by other events, such as volcanic eruptions and meteorites. Tsunamis are waves of energy that radiate from the source at great speeds. If you imagine throwing a rock into a lake, you get some sense of how the tsunami's energy radiates from its source.