Tareas

Earthquake
Earthquakes, also called temblors, can be so tremendously destructive, it’s hard to imagine they occur by the thousands every day around the world, usually in the form of small tremors.
Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "Ring of Fire" because of the preponderance of volcanic activity there as well. Most earthquakesoccur at fault zones, where tectonic plates—giant rock slabs that make up the Earth's upper layer—collide or slide against each other. These impacts are usually gradual and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to thesurface. Other quakes can occur far from faults zones when plates are stretched or squeezed.
Scientists assign a magnitude rating to earthquakes based on the strength and duration of their seismic waves. A quake measuring 3 to 5 is considered minor or light; 5 to 7 is moderate to strong; 7 to 8 is major; and 8 or more is great.
On average, a magnitude 8 quake strikes somewhere every year and some10,000 people die in earthquakes annually. Collapsing buildings claim by far the majority of lives, but the destruction is often compounded by mud slides, fires, floods, or tsunamis. Smaller temblors that usually occur in the days following a large earthquake can complicate rescue efforts and cause further death and destruction.
Loss of life can be avoided through emergency planning, education,and the construction of buildings that sway rather than break under the stress of an earthquake.
Hurricanes

Hurricanes are giant, spiraling tropical storms that can pack wind speeds of over 160 miles (257 kilometers) an hour and unleash more than 2.4 trillion gallons (9 trillion liters) of rain a day. These same tropical storms are known as cyclones in the northern Indian Ocean and Bay ofBengal, and as typhoons in the western Pacific Ocean.
The Atlantic Ocean’s hurricane season peaks from mid-August to late October and averages five to six hurricanes per year.
Hurricanes begin as tropical disturbances in warm ocean waters with surface temperatures of at least 80 degrees Fahrenheit (26.5 degrees Celsius). These low pressure systems are fed by energy from the warm seas. If a stormachieves wind speeds of 38 miles (61 kilometers) an hour, it becomes known as a tropical depression. A tropical depression becomes a tropical storm, and is given a name, when its sustained wind speeds top 39 miles (63 kilometers) an hour. When a storm’s sustained wind speeds reach 74 miles (119 kilometers) an hour it becomes a hurricane and earns a category rating of 1 to 5 on the Saffir-Simpson scale.Hurricanes are enormous heat engines that generate energy on a staggering scale. They draw heat from warm, moist ocean air and release it through condensation of water vapor in thunderstorms.
Hurricanes spin around a low-pressure center known as the “eye.” Sinking air makes this 20- to 30-mile-wide (32- to 48-kilometer-wide) area notoriously calm. But the eye is surrounded by a circular “eyewall” that hosts the storm’s strongest winds and rain.
These storms bring destruction ashore in many different ways. When a hurricane makes landfall it often produces a devastating storm surge that can reach 20 feet (6 meters) high and extend nearly 100 miles (161 kilometers). Ninety percent of all hurricane deaths result from storm surges.
A hurricane’s high winds are also destructive and mayspawn tornadoes. Torrential rains cause further damage by spawning floods and landslides, which may occur many miles inland.
The best defense against a hurricane is an accurate forecast that gives people time to get out of its way. The National Hurricane Center issues hurricane watches for storms that may endanger communities, and hurricane warnings for storms that will make landfall within 24...