10 Natural hazards with the potential to cause chaos
A volcano is an opening on the surface of a planet which allows material warmer than its surroundings to escape from its interior. Volcanoes allow hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
Stratovolcanoes are the majestic giants which have very steep sides and are usually a symmetrical cone shape. Stratovolcanoes erupt viscous lavas which are very sticky and are resistant to flow. This resistance causes allows the volcanoes to have steep sides. Stratovolcanoes produce large violent eruptions and release large plumes of ash in the form of an eruption column. The explosive eruptions are caused by pressure built up in the magma within the volcano. Volcanic eruptions are classified into the Volcanic Explosivity Index or VEI . The VEI is based on the amount of material thrown out of the volcano. Supervolcanoes are the most explosive and dangerous volcanoes on the planet and are classified as a VEI 8. The largest known eruption on Earth was at Yellowstone and occurred 2.2 million years ago. The explosive eruption produced 2500 cubic kilometres of ash, which is about 2500 times more ash than Mount St. Helens .
Lahar is an Indonesian term that describes a hot and cold mixture of water and rock fragments flowing down the slopes of a volcano and/or river valley. Lahars can form in a number of ways: when a small slope collapses and gathers water on the way down from a volcano, through the rapid melting of ice and snow during an eruption, from heavy rainfall on loose volcanic debris and when a volcano erupts through a crater lake. Lahars can contain a large range of volcanic debris, ranging from small clay fragments to large 10m boulders. Travelling at speeds more than 50 miles per hour, lahars move like wet concrete, destroying everything that comes in their path. Since they usually have a volcanic origin, lahars can be up to 80C when they come to rest. Lahars are therefore extremely dangerous for communities living down the slopes of a volcano. In 1984, the Villarrica volcano in Chile erupted and generated small lahars that destroyed a bridge at the base of the volcano.
8 Pyroclastic flows
Pyroclastic flows are a dense mixture of hot, dry rock fragments and hot gases that move away from the vent of an erupted volcano. They are created when stratovolcanoes erupt and create eruption columns of volcanic ash and rock fragments. These columns can reach heights of 30km and maintain their size for tens of hours. As the column loses momentum, it slows and starts to fall back to the ground. The first material to fall to the ground are the large dense rock fragments, followed by lighter ash. The result is a pyroclastic flow consisting of rock fragments, thick ash and toxic gases.
As pyroclastic flows race down the slopes of the volcano, they gain momentum and destroy everything in its path. Travelling at speeds up to 80km per hour and reaching temperatures of 700C, pyroclastic flows are definitely not something you would want to get in the way of.
Earthquakes are one of the deadliest natural hazards. They are produced by the movement of rigid plates which make up the Earth’s crust. Earthquakes generally occur at plate boundaries where either two continental plates collide of where an oceanic plate sinks beneath a continental plate at a subduction zone.Most earthquakes occur along faults which are cracks in a rock which allows movement. When there is movement along a fault, pressure will build up. Once this pressure is too overwhelming, the rocks along the fault will slip and cause an earthquake. The larger the stress build up, the more powerful the earthquake.
Subduction and continental collision zones create intense earthquakes. Some of the largest recorded earthquakes in history have occurred in such zones. In 1960, near Valdivia, a magnitude 9.5 earthquake struck Chile. This earthquake is the largest documented earthquake to hit since accurate measuring devices were made available. An estimated 2,000,000 were left homeless and the costs of damage have been estimated to have been between $3-6 billion today, adjusted for inflation.
Waves of water don’t get much bigger than those of a tsunami. These destructive forces of nature are some of the most dangerous and feared natural hazards on the planet. The word tsunami is a Japanese word which means harbor wave. A tsunami is a series of ocean waves that send surges of water, sometimes reaching heights of over a 100 feet, onto land. Tsunamis are created by large, undersea earthquakes at tectonic plate boundaries. The earthquakes cause the ocean floor to rise and fall which displaces the water column above. This creates waves which propagate outwards in all directions. In deep water, the waves can appear very shallow, having on a few feet in height. When these waves reach shallower water, their amplitudes increase and create large waves. The waves travel up to 500 miles an hour in the ocean and when they reach in the proximity of land, their speeds drastically decrease and cause the wave to build up. Just before the wall of water reaches the shore, there is usually a seaward retreat of all the water. This phenomenon is caused by the trough of the wave, where water is sucked seaward like a vacuum.
A landslide is a mass movement of material, such as a rock, earth or debris, down the slope of a hill or cliff . Landslides can occur in both mountainous areas and areas of generally low relief (LINK17). Landslides can be generated in several ways, the most common cause, however, is water. Slopes that are saturated with water tend to be prone to landslides. Areas, where there is high rainfall, low vegetation and steep slopes, are more likely to generate landslides.
Though water is the primary driving force behind landslides, mountainous areas that are frequently hit by earthquakes, produce large landslides. The occurrence of earthquakes in steep landslide-prone areas greatly increases the likelihood that landslides occur. Humans can indirectly help create landslides by removing vegetation, modifying slopes for construction and vibrations of heavy traffic
Landslide generation can be reduced by not constructing on steep slopes and making sure groundwater is drained away from the landslide-prone areas.
4 Flash floods
Flash flooding happens when rain falls so fast that the underlying ground cannot cope, or drain it away, fast enough. When rain fall outpaces the rate of percolation in the ground, the water will overflow and cause flash floods. In highly developed urban areas, where cement and concrete are dominant, the water has nowhere to go and so flows over the ground. Flash floods can carry cars and houses if they become too powerful. Factors such as topography, rainfall and climate affect the power of a flash flood. Areas that have steep profiles will allow rain water to flow faster downhill. If there is too much rainfall and not enough space for the water to flow, it will break the rivers banks and laterally spread. The climate can affect the rate of percolation and, therefore, play a vital role in how quickly the flash floods are generated. Very dry ground will percolate less water than one with unconsolidated soils.
We have seen lately how sudden and powerful avalanches can be, with the recent earthquake which struck Nepal. These powerful forces of nature can generate lots of momenta and cause havoc for those caught in its path. Most avalanches are slides of dry powdery snow that moves as a formless mass and account for most of the fatalities. Large disastrous avalanches occur when huge slabs of ice break loose, shatter, and race downhill. Like most slides, avalanches are more likely to occur in certain areas than others. Factorssuch as slope angle, temperature, wind and vegetation can help generate avalanches in the right conditions. Once a slope stops, it settles like concrete and, therefore, is vital that victims are rescued quickly.
Ultimately humans are the primary cause for many avalanches. Frequent use of slopes for snow related sports can increase the potential for a slope to fail and create an avalanche. In many cases, there is loss of life and serious injuries to sudden failures on slopes.
Sinkholes are some of the scariest natural hazards around. They usually take thousands of years to form and are usually the result of what are known as karsk processes. Karsk processes involve acidic waters dissolving rocks above or underground. Sinkholes tend form in areas where there are large carbonate layers of strata. As these soluble layers are dissolved they will create open voids beneath the surface and collapse due to instability. What make sinkholes so dangerous is the ability for them to form anywhere, where carbonates layers are present.
Northern parts of Siberia have recently had major news coverage over the formation of large sinkholes. A 35-metre deep sinkhole was discovered in July 2014 after an unexplained eruption that flung soil and rock 120 metres away from the site. The cause for the sinkhole is still unknown, however, the most likely candidate is the release of gas underground, which escaped and erupted.
Tornadoes are some of the most powerful but also the most-chased forces of nature on Earth. Tornadoes are narrow violently rotating columns of air that extends from the base of a thunderstorm to the ground. There are two important aspects needed to create a tornado, geography and rotation. There are three stages in the formation of a tornado. The first stage involves the sunshine heating the ground and causing convection currents to lift the air upwards. The warm air rises and forms low-level shallow cumulus clouds which are trapped under the layer of warm air. They eventually form denser cumulus clouds, known as thunder clouds. At stage one, light debris is twisted and lifted from the ground. At stage two the wind becomes stronger and moves in opposite directions, causing turbulence. As the winds travel higher, they begin to rotate and as the spiral tightens, the winds become increasingly violent . This rotation causes updraft which eventually reaches land and narrows, resulting in faster rotation. This phenomenon is only called a tornado if the spiral updraft touches the land. Over the years, there have been numerous tornadoes which have taken countless lives and tend to destroy anything in their paths.
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