Geography revision

Natural hazards

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Natural hazardsVolcanoesTsunamisTornadoesWildfiresLightning

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Natural hazards

VolcanoesA volcano is a rupture on the crust of a planetary mass object, such as the Earth, which allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

Earth's volcanoes occur because the planet's crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in the Earth's mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates coming together. Volcanoes can also form where there is stretching and thinning of the crust's interior plates, e.g., in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism. Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth. Volcanoes are usually not created where two tectonic plates slide past one another.

Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. One such hazard is that volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature; the melted particles then adhere to the turbine blades and alter their shape, disrupting the operation of the turbine. Large eruptions can affect temperature as ash and droplets of sulphuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated up from the Earth, thereby warming the upper atmosphere (or stratosphere). Historically, so-called volcanic winters have caused catastrophic famines.

Natural hazards

TsunamisA tsunami, also known as a seismic sea wave, is a series of water waves caused by the displacement of a large volume of a body of water, generally an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami.

Tsunami waves do not resemble normal sea waves, because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide, and for this reason they are often referred to as tidal waves. Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called "wave train". Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous and they can affect entire ocean basins; the 2004 Indian Ocean tsunami was among the deadliest and most published natural disasters in human history with at least 290,000 people, including tourists from all over the world killed or missing in 14 countries bordering the Indian Ocean. The 1908 Messina earthquake and tsunami took about 123,000 lives on in Sicily and Calabria, southern Italy but went much less in the public discussion. The difference in attention economy is generally not based on the amount of victims, but in the stability and status of the specific survivor population and its culture of remembrance of a certain disaster.

The Greek historian Thucydides suggested in his late-5th century BC History of the Peloponnesian War, that tsunamis were related to submarine earthquakes, but the understanding of a tsunami's nature remained slim until the 20th century and much remains unknown. Major areas of current research include trying to determine why some large earthquakes do not generate tsunamis while other smaller ones do; trying to accurately forecast the passage of tsunamis across the oceans; and also to forecast how tsunami waves would interact with specific shorelines.

Natural hazards

TornadoesA tornado is a violently rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as twisters or cyclones, although the word cyclone is used in meteorology, in a wider sense, to name any closed low pressure circulation. Tornadoes come in many shapes and sizes, but they are typically in the form of a visible condensation funnel, whose narrow end touches the earth and is often encircled by a cloud of debris and dust. Most tornadoes have wind speeds less than 110 miles per hour (177 km/h), are about 250 feet (76 m) across, and travel a few miles (several kilometers) before dissipating. The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (483 km/h), stretch more than two miles (3.2 km) across, and stay on the ground for dozens of miles (more than 100 km).

Various types of tornadoes include the landspout, multiple vortex tornado, and waterspout. Waterspouts are characterized by a spiraling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud. They are generally classified as non-supercellular tornadoes that develop over bodies of water, but there is disagreement over whether to classify them as true tornadoes. These spiraling columns of air frequently develop in tropical areas close to the equator, and are less common at high latitudes. Other tornado-like phenomena that exist in nature include the gustnado, dust devil, fire whirls, and steam devil; downbursts are frequently confused with tornadoes, though their action is dissimilar.

Tornadoes have been observed on every continent except Antarctica. However, the vast majority of tornadoes occur in the Tornado Alley region of the United States, although they can occur nearly anywhere in North America. They also occasionally occur in south-central and eastern Asia, northern and east-central South America, Southern Africa, northwestern and southeast Europe, western and south-eastern Australia, and New Zealand. Tornadoes can be detected before or as they occur through the use of Pulse-Doppler radar by recognizing patterns in velocity and reflectivity data, such as hook echoes or debris balls, as well as through the efforts of storm spotters.

Natural hazards

WildfiresA wildfire is an uncontrolled fire in an area of combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bush fire, forest fire, desert fire, grass fire, hill fire, peat fire, vegetation fire, and veldfire may be used to describe the same phenomenon depending on the type of vegetation being burned, and the regional variant of English being used. A wildfire differs from other fires by its extensive size, the speed at which it can spread out from its original source, its potential to change direction unexpectedly, and its ability to jump gaps such as roads, rivers and fire breaks. Wildfires are characterized in terms of the cause of ignition, their physical properties such as speed of propagation, the combustible material present, and the effect of weather on the fire.

Wildfires are a common occurrence in Australia; because of the generally hot and dry climate, they pose a great risk to life and infrastructure during all times of the year, though mostly throughout the hotter months of summer and spring. In the United States, there are typically between 60,000 and 80,000 wildfires that occur each year, burning 3 million to 10 million acres of land depending on the year. Fossil records and human history contain accounts of wildfires, as wildfires can occur in periodic intervals. Wildfires can cause extensive damage, both to property and human life, but they also have various beneficial effects on wilderness areas. Some plant species depend on the effects of fire for growth and reproduction, although large wildfires may also have negative ecological effects.

Natural hazards

LightningLightning is a powerful sudden flow of electricity (an electrostatic discharge) accompanied by thunder that occurs during an electric storm. The discharge will travel between the electrically charged regions within a thundercloud, or between a cloud and a cloud, or between a cloud and the surface of a planet. The charged regions within the atmosphere temporarily equalize themselves through a lightning flash, commonly referred to as a strike if it hits an object on the ground. There are three primary types of lightning; from a cloud to itself (intra-cloud or IC); from one cloud to another cloud (CC) and between a cloud and the ground (CG). Although lightning is always accompanied by the sound of thunder, distant lightning may be seen but may be too far away for the thunder to be heard

Natural hazards

HailHail is a form of solid precipitation. It is distinct from sleet, though the two are often confused for one another. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Sleet falls generally in cold weather while hail growth is greatly inhibited at cold temperatures. Unlike graupel, which is made of rime, and ice pellets, which are smaller and translucent, hailstones consist mostly of water ice and measure between 5 millimetres (0.2 in) and 15 centimetres (6 in) in diameter. The METAR reporting code for hail 5 mm (0.20 in) or greater is GR, while smaller hailstones and graupel are coded GS. Hail is possible within most thunderstorms as it is produced by cumulonimbi, and within 2 nautical miles (3.7 km) of the parent storm. Hail formation requires environments of strong, upward motion of air with the parent thunderstorm (similar to tornadoes) and lowered heights of the freezing level. In the mid-latitudes, hail forms near the interiors of continents, while in the tropics, it tends to be confined to high elevations.There are methods available to detect hail-producing thunderstorms using weather satellites and weather radar imagery. Hailstones generally fall at higher speeds as they grow in size, though complicating factors such as melting, friction with air, wind, and interaction with rain and other hailstones can slow their descent through Earth's atmosphere. Severe weather warnings are issued for hail when the stones reach a damaging size, as it can cause serious damage to human-made structures and, most commonly, farmers' crops.

Natural hazards

Natural hazards

Hazard Worst occurrence

Volcano Mt. Tambora, Sumbawa Island, Indonesia

Tsunami The 1958 tsunami that ripped through Lituya Bay

Tornado The Tri-state tornado

Wildfire The Great Peshtigo Fire

Lightning August of 1769, lightning struck the tower of the Church of the Nazaire in Brescia, Italy

Hail 10 April 2001, St. Louis, Missouri, USA

Quiz

1. What is a volcano?a) A mountain with a hole in the topb) A rupture on the crust of a planetary mass

objectc) A lava mountain

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2. Why are wildfires a common occurrence in Australia?a) Australia is the most flammable countryb) To ruin the Australian’s dayc) Because of the generally hot and dry climate

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3.Where do most of the tornadoes happen in the world?a) Tornado Alley in the USAb) Beijing in Chinac) Ethiopia in Africa

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4. What is a tsunami also known as?a) A seismic sea waveb) Tidal wavec) A very big wave

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5.What do the charged regions within the atmosphere do?a) Do nothingb) Touch the groundc) Temporarily equalize themselves through a

lightning flash.

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6.Where are wildfires a common occurrence?a) Africab) Australiac) USA

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7.True or false? Hail is possible in thunderstormsa) Trueb) False

Hail is possible within most thunderstorms as it is produced by cumulonimbi, and within 2 nautical miles (3.7 km) of the parent storm.

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8.True or false? Volcanic eruptions can cause tsunamisa) Trueb) False Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami.

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9.True or False? In the United States, , there are typically between 100 and 200 wildfires that occur each year.a) Trueb) FalseIn the United States, there are typically between 60,000 and 80,000 wildfires that occur each year, burning 3 million to 10 million acres of land depending on the year.

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10.True or False? The METAR reporting code for hail 5 mm (0.20 in) or greater is GRa) Trueb) FalseSmaller hailstones and graupel are coded GS.

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