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Major U.S. Epidemics

Here's a list of the major outbreaks in U.S history, including locations and the number of deaths. 1793Philadelphia: more than 4,000 residents died from yellow fever.1832July–Aug., New…

The Continents

A continent is defined as a large unbroken land mass completely surrounded by water, although in some cases continents are (or were in part) connected by land bridges. The seven continents ar…

Volcanoes of the World

The Nature of VolcanoesRecent Volcanic ActivityThe Deadliest Volcanic EruptionsPrincipal Types of VolcanoesEarth's Greatest Volcanic FieldSource: U.S. Dept. of the Interior, Geological Survey …

Cinder Cones

Cinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, i…

Composite Volcanoes

Composite volcanoes, sometimes called stratovolcanoes, are typically deep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks,…

Shield Volcanoes

Shield volcanoes are built almost entirely of fluid lava flows. Flow after flow pours out in all directions from a central summit vent, or group of vents, building a broad, gently sloping con…

Lava Domes

Volcanic or lava domes are formed by relatively small, bulbous masses of lava too viscous to flow any great distance; consequently, on extrusion, the lava piles over and around its vent. A do…

Submarine Volcanoes

Submarine volcanoes and volcanic vents are common features on certain zones of the ocean floor. Some are active at the present time and, in shallow water, disclose their presence by blasting …

Earth's Greatest Volcanic Field

The largest known concentration of active volcanoes on Earth was discovered by scientists aboard the research vessel Melville (Nov. 1992–Jan. 1993). The vast volcanic cluster is situate…

Continental Drift and Plate-Tectonics Theory

Source: U.S. Dept. of the Interior, Geological Survey According to the theory of continental drift, the world was made up of a single continent through most of geologic time. That continent ev…