Naturalhazards are major events that are caused by natural earth processes. Sincethere is no human interference when natural hazards occur, it is difficult forhumans to prevent their occurrence. Some of the natural hazards are such asvolcanic eruptions, floods, tsunamis, and earthquakes.
In the following paper,tsunamis, volcanic eruptions, and weathering have been singled out for discussionand their impact on human lives.Atsunami refers to a series of waves that are caused by violent movement of thesea floor. The cause of tsunamis is any large or impulsive displacement of theseabed level.
The movements of the sea floor may be the result of eitherearthquakes, landslides, or volcanic eruption. As such, there are three typesof tsunamis. The most common is earthquake tsunamis. These are caused bysubmarine faulting that result from large earthquakes. When an inclined area ofthe ocean floor is suddenly thrust upwards or sideways, or a block of the oceanfloor suddenly drops or is thrown upwards, the result is an earthquake referredto as a “tsunamigenic earthquake”. Amajority of tsunamigenic earthquakes occur in the great ocean trenches wherethe tectonic plates making up the earth’s surface collide.
In certaininstances, the plates catch and the motion below the trench becomes hung. Insuch an instance, the result is a “seismic gap” where there are no earthquakes.However, as the overall motion of the plates continues, there is a built-uptension that when released results in the generation of a large earthquake.
Although,when there is a horizontal sea floor movement, there is no tsunami generated.The most critical earthquakes for tsunami generation are those with magnitudesabove 6.5.
Other than magnitude, other underlying factors that determine theextent to which a tsunami causes havoc are yet to be scientifically explained.For example, while in 2004 an earthquake of a magnitude of 9.3 caused colossaldamage just off the coast of Sumatra, Indonesia, an 8.7 magnitude earthquake atthe same spot in 2005 went without resulting in any significant tsunami. Thesecond cause of tsunamis is those that are the result of landslides. Tsunamismay result from landslides that start at sea level and plunge into the sea orwhen a landslide is entirely under water. The landslides occur when deposits ofsediment become too steep to an extent that the material is pulled by gravity.The slope failures can be the result of storms, earthquakes or merely excessivedeposits of material on the slope.
There are certain environments such as riverdeltas and steep underwater slopes that lie above sub-marine canyons that havea high likelihood of resulting in landslides. Thethird category of tsunamis is the tsunamis produced because of volcaniceruptions. While they are rare, they are very destructive. They may be theresult of submarine explosions, collapse of volcanic caldera, or pyroclasticflows. Submarine volcanic explosions are the result of a violent interactionbetween hot volcanic magma and seawater resulting in streams of explosions. Whenunderwater explosions occur at depths of less than 1500 feet, they may disturbthe water all the way to the surface and result in tsunamis. For pyroclasticflows, they are ground-hugging clouds that are driven by gravity and fluidisedby hot gases. They can move rapidly into the ocean and they displace seawaterto result in tsunami.
Further, when a volcanic caldera collapses, it can resultin a tsunami. This occurs when there is a sudden subsidence of volcanic edificedisplacing water to result in tsunami waves. Weatheringrefers to any physical or chemical reaction occurring at the interface of arock’s surface and the atmosphere to an extent that the rock decomposes ordisintegrates.
The rocks and minerals are converted into new chemicalcombinations that are stable under the new conditions. Chemicalweathering or decomposition is a major way in which rocks are prepared forerosion and transportation. It first forms new minerals that are less resistantto erosion. Secondly, it creates new mineral substances through chemicalreactions, which often involve water. The volume continues to increase andresults in expansion hence fracturing the rocks.
As the volume increases, itaccelerates physical and chemical weathering since the surface of the rock isexposed and the rock mass is weakened. Further the chemical weathering dissolvesminerals in a chemically active water solution which makes them easy to removefor transportation. The number of pore spaces continues to increase as theweathering pace increases.
One of the most essential components in this processis water. When water is present, there is an increased rate of chemicalweathering. It is for this reason that chemical weathering is most common inhumid areas. Also, there is an increase in the intensity of chemical reactionswhen there is high temperature. Chemical weathering due to water is calledhydrolysis. It occurs when sedimentary rocks absorb water and decay owing tointernal pressure. Another chemical weathering process is oxidation wherematerial formed of iron begins to rust owing to exposure to water and oxygen.Another is carbonation where water combines with carbon resulting in carbonicacid which dissolves limestone and other carbonic landscapes.
Physicalweathering simply refers to the process of breaking of rocks into smallerpieces. There are four main types of physical weathering. The first is frostwedging which is the result of alternating between freezing and thawing ofwater in cracks and fractures hence promoting disintegration of rocks.
Thesecond is unloading. In this case, exfoliation of metamorphic and igneous rocksoccurs at the surface of the earth owing to reduction in confining pressure.The third is thermal expansion where the cracking of rocks results fromalternate expansion and contraction because of heating and cooling. Finally,biological actions such as the growth of plant roots or the stampede of animalsresult in physical weathering.Whenphysical or chemical weathering occurs, the sizes of the rocks and the forcesthat control their physical movements are reduced. When they exist, glaciersbecome powerful sculpting and agents of erosion.
In fact, weathering followedby erosion is the origin of the landscape of New England and Long Island andthe great lakes. Further, they are the reason behind half of North Americaisostatically rebounding upwards. After weathering, wind can transport largevolumes of material. The result of such a situation is the creation ofdestructive dust bowls. An example is the 1940s dustbowl in New Mexico and itssurroundings. This resulted in the covering of whole farms and houses.
Over 100million acres of land were affected by the Dust Bowl. They resulted in therelocation of over 300 thousand people from California as their lands weretotally damaged.Further, they were a health risk as they caused dustpneumonia.
During the Dust Bowl, over 6500 people were killed during only oneyear. Otherthan wind, flowing water easily carries the already weathered material. Infact, water is the main cause of the current West Virginia topography.
Mostlandscape sculpting results from a combination of streams and mass wastingwhere the water is responsible for the shape of the valley floor while thevalley walls are the result of the winds. Magmaforms in the deep parts of the earth’s crust and the upper parts of the mantlewhere there is high pressure and temperatures. The magma forms when there arechanges in temperature and pressure. Under normal temperature and pressure, therock in the mantle does not melt because of high pressure. When earth movementscause a decrease in pressure, magma forms. Since magma is less dense than thesolid rock that forms it, it rises towards the surface and erupts.In the figure below,using the areas where major volcanic activities have taken place, it ispossible to determine how volcanoes form.
The map shows that these are mainlythe boundaries between tectonic plates. The Pacific Ocean for example isreferred to as the Ring of Fire since it has some of the most active volcanoesin the world. About 15% of active volcanoes occur on lands where platesseparate while 80% occur where the plates collide. A few others occur in areasthat are far from the tectonic plates. Atthe divergent boundary, tectonic plates move away from each other. This resultsin the creation of a set of deep cracks that are called rift zone between theplates. The gap that is left is filled by mantle rocks.
When these mantle rocksget near, there is a reduction in pressure which causes the mantle rock to meltand form magma. The magma then finds its way through the rift zones and erupts.Most of the divergent boundaries are on the sea floor. The magna that flowsfrom the undersea results in volcanoes and mountain chains which are calledmid-ocean ridges.
Onthe other hand, at convergent boundaries, tectonic plates collide. At a pointwhen an oceanic plate collides with a continental late, the oceanic plateslides under the continental plate in a process called subduction. Since theoceanic crust is denser than the continental crust, it sinks into the mantle.As it sinks, there is an increase in pressure and temperature. Since the oceancrust forms below the ocean, the rock has a lot of water and the heat on itleads to water being released. The mantle rock when mixed with water can meltat lower temperatures.
When it melts, magma rises to the surface leading to aneruption.Oneof the places with the most complex tectonics is Indonesia. It is the meetingpoint of several tectonic plates. First, it is located between two continentalplates namely Eurasian Plate and Australian Plate. It is also between twooceanic plates, the Pacific Plate and the Philippines Sea Plate. In WesternIndonesia, the subduction of the Indian Oceanic plate beneath the Eurasiancontinental plate results in the most seismically active area on the globe andis referred to as the volcanic arc.
In May 2016, the eruption of Mount Sinabungin Western Indonesia led to the death of several people. The deaths of most ofthe people was a result of being hit by pyroclastic clouds which reach up to700 degrees Celsius when they come from the volcano. Asexplained, not all volcanoes occur at the plate boundaries. Others occur at thecentre such as the Hawaii Islands volcanoes. These are called hot spot areas.The hot spots are places on the earth surface where volcanoes occur far fromplate boundaries. Hot spots are mostly found above hot columns of mantle rockcalled mantle plumes.
There are long chains of volcanoes occurring on mantlerocks. Scientists believe that the mantle plumes remain in a single spot whilethe tectonic plate moves over it which leads to the specific areas beingconsistent in forming of volcanoes. Overthe years, millions of people have died due to natural hazards and propertyworth trillions of dollars lost. For this reason, several ways are important inmitigating to reduce the impacts of natural disasters.
First, public spendingmust ensure that infrastructure such as bridges are functioning in the rightway. This makes it easy to conduct rescue missions when people are trappedafter a disaster. Secondly, there is need to undertake the process of mappinghazards, vulnerability, and modelling risk.
Through this, certain areas can becordoned off so that individuals to avoid risks do not access them. This isespecially important in areas where there are active volcanoes. Further,governments should take advantage of technological advances to predict some ofthe natural disasters. This will ensure that the general population undertakesa certain level of preparedness to avoid the risks that are eminent with thenatural hazards.