Geohazards

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