Natural steep underwater slopes that lie above sub-marine
hazards are major events that are caused by natural earth processes. Since
there is no human interference when natural hazards occur, it is difficult for
humans to prevent their occurrence. Some of the natural hazards are such as
volcanic eruptions, floods, tsunamis, and earthquakes. In the following paper,
tsunamis, volcanic eruptions, and weathering have been singled out for discussion
and their impact on human lives.
tsunami refers to a series of waves that are caused by violent movement of the
sea floor. The cause of tsunamis is any large or impulsive displacement of the
seabed level. The movements of the sea floor may be the result of either
earthquakes, landslides, or volcanic eruption. As such, there are three types
of tsunamis. The most common is earthquake tsunamis. These are caused by
submarine faulting that result from large earthquakes. When an inclined area of
the ocean floor is suddenly thrust upwards or sideways, or a block of the ocean
floor suddenly drops or is thrown upwards, the result is an earthquake referred
to as a “tsunamigenic earthquake”.
majority of tsunamigenic earthquakes occur in the great ocean trenches where
the tectonic plates making up the earth’s surface collide. In certain
instances, the plates catch and the motion below the trench becomes hung. In
such 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-up
tension 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 magnitudes
above 6.5. Other than magnitude, other underlying factors that determine the
extent 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 colossal
damage just off the coast of Sumatra, Indonesia, an 8.7 magnitude earthquake at
the same spot in 2005 went without resulting in any significant tsunami.
second cause of tsunamis is those that are the result of landslides. Tsunamis
may result from landslides that start at sea level and plunge into the sea or
when a landslide is entirely under water. The landslides occur when deposits of
sediment 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 excessive
deposits of material on the slope. There are certain environments such as river
deltas and steep underwater slopes that lie above sub-marine canyons that have
a high likelihood of resulting in landslides.
third category of tsunamis is the tsunamis produced because of volcanic
eruptions. While they are rare, they are very destructive. They may be the
result of submarine explosions, collapse of volcanic caldera, or pyroclastic
flows. Submarine volcanic explosions are the result of a violent interaction
between hot volcanic magma and seawater resulting in streams of explosions. When
underwater explosions occur at depths of less than 1500 feet, they may disturb
the water all the way to the surface and result in tsunamis. For pyroclastic
flows, they are ground-hugging clouds that are driven by gravity and fluidised
by hot gases. They can move rapidly into the ocean and they displace seawater
to result in tsunami. Further, when a volcanic caldera collapses, it can result
in a tsunami. This occurs when there is a sudden subsidence of volcanic edifice
displacing water to result in tsunami waves.
refers to any physical or chemical reaction occurring at the interface of a
rock’s surface and the atmosphere to an extent that the rock decomposes or
disintegrates. The rocks and minerals are converted into new chemical
combinations that are stable under the new conditions.
weathering or decomposition is a major way in which rocks are prepared for
erosion and transportation. It first forms new minerals that are less resistant
to erosion. Secondly, it creates new mineral substances through chemical
reactions, which often involve water. The volume continues to increase and
results in expansion hence fracturing the rocks. As the volume increases, it
accelerates physical and chemical weathering since the surface of the rock is
exposed and the rock mass is weakened. Further the chemical weathering dissolves
minerals in a chemically active water solution which makes them easy to remove
for transportation. The number of pore spaces continues to increase as the
weathering pace increases. One of the most essential components in this process
is water. When water is present, there is an increased rate of chemical
weathering. It is for this reason that chemical weathering is most common in
humid areas. Also, there is an increase in the intensity of chemical reactions
when there is high temperature. Chemical weathering due to water is called
hydrolysis. It occurs when sedimentary rocks absorb water and decay owing to
internal pressure. Another chemical weathering process is oxidation where
material formed of iron begins to rust owing to exposure to water and oxygen.
Another is carbonation where water combines with carbon resulting in carbonic
acid which dissolves limestone and other carbonic landscapes.
weathering simply refers to the process of breaking of rocks into smaller
pieces. There are four main types of physical weathering. The first is frost
wedging which is the result of alternating between freezing and thawing of
water in cracks and fractures hence promoting disintegration of rocks. The
second is unloading. In this case, exfoliation of metamorphic and igneous rocks
occurs at the surface of the earth owing to reduction in confining pressure.
The third is thermal expansion where the cracking of rocks results from
alternate expansion and contraction because of heating and cooling. Finally,
biological actions such as the growth of plant roots or the stampede of animals
result in physical weathering.
physical or chemical weathering occurs, the sizes of the rocks and the forces
that control their physical movements are reduced. When they exist, glaciers
become powerful sculpting and agents of erosion. In fact, weathering followed
by erosion is the origin of the landscape of New England and Long Island and
the great lakes. Further, they are the reason behind half of North America
isostatically rebounding upwards. After weathering, wind can transport large
volumes of material. The result of such a situation is the creation of
destructive dust bowls. An example is the 1940s dustbowl in New Mexico and its
surroundings. This resulted in the covering of whole farms and houses. Over 100
million acres of land were affected by the Dust Bowl. They resulted in the
relocation of over 300 thousand people from California as their lands were
Further, they were a health risk as they caused dust
pneumonia. During the Dust Bowl, over 6500 people were killed during only one
than wind, flowing water easily carries the already weathered material. In
fact, water is the main cause of the current West Virginia topography. Most
landscape sculpting results from a combination of streams and mass wasting
where the water is responsible for the shape of the valley floor while the
valley walls are the result of the winds.
forms in the deep parts of the earth’s crust and the upper parts of the mantle
where there is high pressure and temperatures. The magma forms when there are
changes in temperature and pressure. Under normal temperature and pressure, the
rock in the mantle does not melt because of high pressure. When earth movements
cause a decrease in pressure, magma forms. Since magma is less dense than the
solid 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 is
possible to determine how volcanoes form. The map shows that these are mainly
the boundaries between tectonic plates. The Pacific Ocean for example is
referred to as the Ring of Fire since it has some of the most active volcanoes
in the world. About 15% of active volcanoes occur on lands where plates
separate while 80% occur where the plates collide. A few others occur in areas
that are far from the tectonic plates.
the divergent boundary, tectonic plates move away from each other. This results
in the creation of a set of deep cracks that are called rift zone between the
plates. The gap that is left is filled by mantle rocks. When these mantle rocks
get near, there is a reduction in pressure which causes the mantle rock to melt
and 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 flows
from the undersea results in volcanoes and mountain chains which are called
the other hand, at convergent boundaries, tectonic plates collide. At a point
when an oceanic plate collides with a continental late, the oceanic plate
slides under the continental plate in a process called subduction. Since the
oceanic 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 ocean
crust forms below the ocean, the rock has a lot of water and the heat on it
leads to water being released. The mantle rock when mixed with water can melt
at lower temperatures. When it melts, magma rises to the surface leading to an
of the places with the most complex tectonics is Indonesia. It is the meeting
point of several tectonic plates. First, it is located between two continental
plates namely Eurasian Plate and Australian Plate. It is also between two
oceanic plates, the Pacific Plate and the Philippines Sea Plate. In Western
Indonesia, the subduction of the Indian Oceanic plate beneath the Eurasian
continental plate results in the most seismically active area on the globe and
is referred to as the volcanic arc. In May 2016, the eruption of Mount Sinabung
in Western Indonesia led to the death of several people. The deaths of most of
the people was a result of being hit by pyroclastic clouds which reach up to
700 degrees Celsius when they come from the volcano.
explained, not all volcanoes occur at the plate boundaries. Others occur at the
centre 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 from
plate boundaries. Hot spots are mostly found above hot columns of mantle rock
called mantle plumes. There are long chains of volcanoes occurring on mantle
rocks. Scientists believe that the mantle plumes remain in a single spot while
the tectonic plate moves over it which leads to the specific areas being
consistent in forming of volcanoes.
the years, millions of people have died due to natural hazards and property
worth trillions of dollars lost. For this reason, several ways are important in
mitigating to reduce the impacts of natural disasters. First, public spending
must ensure that infrastructure such as bridges are functioning in the right
way. This makes it easy to conduct rescue missions when people are trapped
after a disaster. Secondly, there is need to undertake the process of mapping
hazards, vulnerability, and modelling risk. Through this, certain areas can be
cordoned off so that individuals to avoid risks do not access them. This is
especially important in areas where there are active volcanoes. Further,
governments should take advantage of technological advances to predict some of
the natural disasters. This will ensure that the general population undertakes
a certain level of preparedness to avoid the risks that are eminent with the