Read the text about natural disasters

Natural Disasters

http://environment.nationalgeographic.com/environment/natural-disasters

Avalanches

While avalanches are sudden, the warning signs are almost always numerous before they let loose. Yet in 90 percent of avalanche incidents, the snow slides are triggered by the victim or someone in the victim's party. Avalanches kill more than 150 people worldwide each year. Most are snowmobilers, skiers, and snowboarders.

Many avalanches are small slides of dry powdery snow that move as a formless mass. These "sluffs" account for a tiny fraction of the death and destruction wrought by their bigger, more organized cousins. Disastrous avalanches occur when massive slabs of snow break loose from a mountainside and shatter like broken glass as they race downhill. These moving masses can reach speeds of 130 kilometers per hour within about five seconds. Victims caught in these events seldom escape. Avalanches are most common during and in the 24 hours right after a storm that dumps 30 centimeters or more of fresh snow. The quick pileup overloads the underlying snowpack, which causes a weak layer beneath the slab to fracture. The layers are an archive of winter weather: big dumps, drought, rain, a hard freeze, and more snow. How the layers bond often determines how easily one will weaken and cause a slide.

Storminess, temperature, wind, slope steepness and orientation (the direction it faces), terrain, vegetation, and general snowpack conditions are all factors that influence whether and how a slope avalanches. Different combinations of these factors create low, moderate, considerable, and high avalanche hazards.

Hurricanes

Hurricanes are giant, spiraling tropical storms that can pack wind speeds of over 257 kilometers an hour and unleash more than 9 trillion liters of rain a day. These same tropical storms are known as cyclones in the northern Indian Ocean and Bay of Bengal, 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 26.5 degrees Celsius. These low pressure systems are fed by energy from the warm seas. If a storm achieves wind speeds of 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 63 kilometers an hour. When a storm’s sustained wind speeds reach 119 kilometers an hour it becomes a hurricane and earns a category rating of 1 to 5 on the Saffir-Simpson scale.

Earthquakes

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 earthquakes occur 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 the surface. 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 some 10,000 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.

Tornadoes

Tornadoes are vertical funnels of rapidly spinning air. Their winds may top 400 kilometers an hour and can clear-cut a pathway 1.6 kilometers wide and 80 kilometers long. Twisters are born in thunderstorms and are often accompanied by hail. Giant, persistent thunderstorms called supercells spawn the most destructive tornadoes.

These violent storms occur around the world, but the United States is a major hotspot with about a thousand tornadoes every year. "Tornado Alley," a region that includes eastern South Dakota, Nebraska, Kansas, Oklahoma, northern Texas, and eastern Colorado, is home to the most powerful and destructive of these storms. U.S. tornadoes cause 80 deaths and more than 1,500 injuries per year.

Lightning

Contrary to the common expression, lightning can and often does strike the same place twice, especially tall buildings or exposed mountaintops. Cloud-to-ground lightning bolts are a common phenomenon – about 100 strike Earth’s surface every single second – yet their power is extraordinary. Each bolt can contain up to one billion volts of electricity.

This enormous electrical discharge is caused by an imbalance between positive and negative charges. During a storm, colliding particles of rain, ice, or snow increase this imbalance and often negatively charge the lower reaches of storm clouds. Objects on the ground, like steeples, trees, and the Earth itself, become positively charged – creating an imbalance that nature seeks to remedy by passing current between the two charges.

A step-like series of negative charges, called a stepped leader, works its way incrementally downward from the bottom of a storm cloud toward the Earth. Each of these segments is about 46 meters long. When the lowermost step comes within 46 meters of a positively charged object it is met by a climbing surge of positive electricity, called a streamer, which can rise up through a building, a tree, or even a person. The process forms a channel through which electricity is transferred as lightning.

Tsunamis

The most infamous tsunami of modern times hit Indian Ocean shorelines on the day after Christmas 2004. That tsunami is believed to have packed the energy of 23,000 Hiroshima-type atomic bombs. Some 150,000 people were killed in a single day. A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 30.5 meters, onto land. These walls of water can cause widespread destruction when they crash ashore.

These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly it displaces the water above it and launches the rolling waves that will become a tsunami.

10.3 Answer the following questions:

· What usually triggers avalanches?

· How do they get formed?

· When do avalanches usually form?

· What is a hurricane?

· What other terms can be used for a hurricane?

· What are necessary conditions and stages of hurricane formation?

· Where do most earthquakes on Earth occur? Why?

· How often do great quakes occur?

· What can aggravate the consequences of the quake?

· What is a tornado?

· What is the major hotspot for tornadoes in the world?

· Can lightning strike the same place twice?

· What causes lightning?

· Where do most of tsunamis occur?

· Why are tsunamis dangerous?

· What causes a tsunami?

10.4 Fill in the gaps with the words and expressions given below. Translate the text.

devastation, dwarf, false alarms, gravitational force, high-energy event, inland, magnitude, monitor, propagates, recede, runup, seismographs, sirens, site of impact, slosh, trough, tsunami detection, underwater earthquakes, wavelength

Tsunami

A tsunami is a series of huge waves that can cause great _________ and loss of life when they strike a coast.

Tsunamis are caused by an underwater earthquake, a volcanic eruption, a sub-marine rockslide, or, more rarely, by an asteroid or meteoroid crashing into in the water from space. Most tsunamis are caused by _________, but not all underwater earthquakes cause tsunamis – an earthquake has to be over about _________ 6.75 on the Richter scale for it to cause a tsunami. About 90 percent of all tsunamis occur in the Pacific Ocean.

Many tsunamis could be detected before they hit land, and the loss of life could be minimized, with the use of modern technology, including _________ (which detect earthquakes), computerized offshore buoys that can measure changes in wave height, and a system of sirens on the beach to alert people of potential tsunami danger.

Note: If you see the water _________ quickly and unexpectedly from a beach (this is called drawback), run toward higher ground or inland – there may be a tsunami coming. Also, if you are on the coast and there is an earthquake, it may have caused a tsunami, so run toward higher ground or inland. Some beaches have tsunami warning _________ – do not ignore them. The first wave in a tsunami is often not the largest; if you experience one abnormally-huge wave, go _________ quickly – even bigger waves could be coming soon.

The Word “Tsunami”:The word tsunami comes from the Japanese word meaning “harbor wave”. Tsunamis are sometimes incorrectly called “tidal waves” – tsunamis are not caused by the tides (tides are caused by the _________ of the moon on the sea). Regular waves are caused by the wind.

The Development of a Tsunami:A tsunami starts when a huge volume of water is quickly shifted. This rapid movement can happen as the result of an underwater earthquake (when the sea floor quickly moves up or down), a rock slide, a volcanic eruption, or another _________.

After the huge volume of water has moved, the resulting wave is very long (the distance from crest to crest can be hundred of miles long) but not very tall (roughly 3 feet tall). The wave _________ (spreads) across the sea in all directions; it can travel great distances from the source at tremendous speeds.

The Size of a Tsunami:Tsunamis have an extremely long _________ (it is the distance between the crest (top) of one wave and the crest of the next wave) – up to several hundred miles long. The period (the time between two successive waves) is also very long – about an hour in deep water.

In the deep sea, a tsunami's height can be only about 1 m tall. Tsunamis are often barely visible when they are in the deep sea. This makes _________ in the deep sea very difficult.

The Speed of a Tsunami:A tsunami can travel at well over 970 kph in the open ocean – as fast as a jet flies. It can take only a few hours for a tsunami to travel across an entire ocean. A regular wave (generated by the wind) travels at up to about 90 km/hr.

A Tsunami Hits the Coast:As a tsunami wave approaches the coast (where the sea becomes shallow), the _________ (bottom) of a wave hits the beach floor, causing the wave to slow down, to increase in height (the amplitude is magnified many times) and to decrease in wavelength (the distance from crest to crest).

At landfall, a tsunami wave can be hundreds of meters tall. Steeper shorelines produce higher tsunami waves.

In addition to large tsunami waves that crash onto shore, the waves push a large amount of water onto the shore above the regular sea level (this is called runup). The _________ can cause tremendous damage inland and is much more common than huge, thundering tsunami waves.

Tsunami Warning Systems: Tsunami warning systems exist in many places around the world. As scientists continuously _________ seismic activity (earthquakes), a series of buoys float off the coast and monitor changes in sea level. Unfortunately, since tsunamis are not very tall in height when they are out at sea, detection is not easy and there are many _________. Sirens at affected beaches may be activated – do not ignore them!

Wind-Generated Waves vs. Tsunami Waves:Regular waves (caused by the wind) are very different from tsunami waves. Tsunami waves are much faster than wind-generated waves and they have a much longer wavelength. In the deep sea, tsunami waves are very small, but by the coast, they _________ regular waves.

How often do tsunamis occur?Tsunamis are very rare. There are roughly six major tsunamis each century.

Tiny Model of a Tsunami:You can make a tiny model of a tsunami by dropping a rock into a bowl of water, causing ripples to travel outwards from the _________. Another way is to slightly jolt the bowl of water and watch it _________ over the rim on one side.