GEOHAZARDS
Everything you need to know about Geohazards
by Jevish Sydamah…
WHAT IS GEOHAZARDS?
A Geohazard is any natural hazard that is caused by the Earth, for example
volcanoes, earthquakes, floods, tsunamis and cyclones. These and other
Geohazards can cause great loss of life and damage to property when they occur
so governments are always looking for ways of reducing the impacts of
Geohazards. It is sometimes possible to predict when certain Geohazards will
occur, such as volcanoes and cyclones. For example the eruption of a volcano can
be predicted when scientists observe the following warning signs:
1. The gases that volcanoes give off suddenly change.
2. Small earthquakes happen in the local area.
3. The volcano starts to get bigger as it fills with magma.
EARTHQUAKES
Earthquakes: Fractures in Earth's crust, or lithosphere (its crust and
upper mantle), where sections of rock have slipped past each other are
called faults. Earthquakes are caused by the sudden release of
accumulated strain along these faults, releasing energy in the form of
low-frequency sound waves called seismic waves. A major earthquake are
usually followed by aftershocks. The epicentres of large earthquakes are
normally located along known seismically active zones, although the
disruptive effects of an earthquake may extend over areas 100s of
kilometres away. Earthquakes may cause liquefaction, landslides, marine
landslides and tsunamis.
VOLCANOES
Volcanoes: A volcano is defined by an opening in the Earth's
crust from which lava, ash, and hot gases flow or are ejected
during an eruption. Volcanic hazards vary from one volcano to
another and from one eruption to the next. The big killers are
pyroclastic flows, lahars, and tsunamis triggered by volcanic
eruptions. The most frequent lethal events are so-called tephra
explosions – very rapid jets of lava . The longest-lasting damage
is usually inflicted by thick lava flows or major collapses of
volcanic edifices, as at Mt. St. Helens in 1980.
LANDSLIDES
Landslides: A landslide is a Geohazard that involves the breakup
and downhill flow of rock, mud, water and anything caught in the
path. Landslides are one of the main processes by which landscapes
evolve and the related hazards result in a complex, changing
landscape. Landslides both vary enormously in their distribution in
space and time, the amounts of energy produced during the activity
and especially in size. This means that the resulting surface
deformation or displacement varies considerably from one type of
instability (that trigger the breakup) to another. Individual ground
instabilities may have a common trigger, such as an extreme rainfall
event or an earthquake, and therefore occur alongside many
equivalent occurrences over a large area. This means that they can
have a significant regional impact.
TSUNAMIS
Tsunamis: Tsunamis are gravity waves (different physical
features than wind induced surface waves) created by a rapid
displacement of a water column. The displacement can be the
result of earthquakes, volcanic eruptions or landslides. These
energetic waves travel fast with long wavelengths and relatively
small amplitudes in open ocean. When hitting shallow water they
build up an amplitude and can become tens, and on very rare
occasions, even hundreds of meters high. The coastal inundation
can be devastating and catastrophic.
EXTREME GEOHAZARDS
Extreme Geohazards
The Sumatran earthquake/Indian ocean tsunami was one of the most extreme
Geohazard in modern history . This extreme reached us all, beyond the mere
geophysical waves. As tourists come from all over the world to visit the beautiful
shores of the Indian ocean, the 2004 tsunami affected people from around the
globe. The extent of it's destruction and the dimension of the disaster are parts of
the definition of extreme. That, combined with their physical features that
normally are several orders higher or more powerful than the average
Geohazard. So, when we talk about extreme Geohazards we not only refer to the
physical characteristics of the Geohazard but also the risk they represent in
terms of consequences of this hazard.
MEGA TSUNAMIS AND SUPER VOLCANOES
Really extreme Geohazards – mega tsunamis and super volcanoes
Norway is situated in a safe distance from the Ring of Fire. Crustal
movements in this part of the world are very slow stemming from post
glacial rebound, the uplift of ground due to the absence of heavy glaciers
that melted thousands of years ago. Norway has in fact a rather high
number of earthquakes as well but these far from qualify as extreme
Geohazards. But, if we look at the geological history of Norway we find
evidence of a really extreme Geohazard. More than 8000 years ago, the
submarine Storegga landslide caused a wide ranging mega tsunami
hitting most of our entire coastline.
EXAMPLE OF A GEOHAZARD
Submarine) Landslides
Debris flows
Shallow gas accumulation
Overpressured zones (including gas and shallow water flows)
Naturally occurring gas hydrates and their climate-controlled meta-
stability
Mud flows, diapirism and mud volcanism/mud volcanoes
Earthquakes and seismicity
Tsunamis from tectonics and landslides
Rock falls and landslides
STATS CAUSED BY GEOHAZARDS
The World Disasters Report 2005 estimated that in 2004, over 250,000 were
reported killed by natural disasters—mostly from the Indian Ocean tsunami in
December. Disasters affected 146 million persons and inflicted estimated
damage of US$ 100-145 billion. From 1995 to 2004, about 6,000 reported
disasters killed over 900,000, affected over 2.5 billion persons, and caused at
least US$ 738 billion in estimated damage . This compares to 640,000
reported killed and 1.74 billion reported affected by natural disasters from
1985 to 1994. Over the decade, 51 people died per natural disaster event in
countries of high human development (as defined by United Nations
Development Program), compared to 573 deaths per event in countries of low
human development.
PHOTOS…
STRUCTURE…
GEOHAZARD RESOURCE…
VOLCANO…
LANDSLIDE…
TSUNAMI…
EARTHQUAKE…
HOPE YOU ENJOYED THE PRESENTATION.THANK YOU FOR READING…BY JEVISH SYDAMAH