Cross-references
Geologic Time Scale
Marine Microfossils
Radiocarbon: Clock and Tracer
Sclerochronology
GEOHAZARDS: COASTAL DISASTERS
Gösta Hoffmann and Klaus Reicherter
Department of Geosciences and Geography, RWTH
Aachen University, Aachen, Germany
Definition
We define the term “hazard” as a potential source of harm,
where “harm” is defined as the “injury or damage to the
health of people, or damage to property or the environment” following the definition as given by ISO/IEC
(2014). The term “risk” is defined as a “combination of
the probability of occurrence of harm and the severity of
that harm” (ISO/IEC, 2014). Furthermore, the term “risk”
may be expressed as a function of hazard, exposure, and
vulnerability. A geohazard is a geological state that may
lead to widespread damage presenting severe threats to
humans, property, and the natural and built environment.
A coastal geohazard is a natural physical phenomenon
usually associated with seacoasts but to a limited extent
also along lakeshores, where the initiating process of the
disaster may originate at great distances from the point
of impact.
Introduction
There are numerous geohazards which affect coastal
regions, including beach erosion, landslide/cliff collapse,
wave attack, flooding, and tsunamis. They are always
related to the landward movement of water. These processes can be either slow or fast and may be temporary
or permanent in nature. Some hazards have meteorological causes (climatic hazards, e.g., storms, Nicholls,
2004), whereas others may be driven by Earth’s endogenous forces such as seismic events (earthquakes and tsunamis, e.g., Atwater, 1987) and volcanic eruptions (e.g.,
Firth et al., 1996). Furthermore, coastal hazards can be
gravity induced (landslide/cliff collapse, e.g., Dawson
et al., 2009; Del Río and Gracia, 2009). Relative sea-level
changes may pose a hazard to many low-lying countries as
do subsurface changes induced by humans (e.g., due to
groundwater extraction and associated settlement). As
the coastal zone is a preferred area of human settlement,
there is always some exposure to coastal hazards. Coastal
cities host many different kinds of economically relevant
infrastructure (e.g., harbors) and are often used for recreational purposes. Two percent of the world’s surface is
defined as low elevation coastal zone (LECZ).
McGranahan et al. (2007) defined the LECZ as a
contiguous area along the coast lower than 10 m above
sea-level that is inhabited by 10 % of the world’s population. Small and Nicholls (2003) estimate that around 1.2
billion people are living within 100 km of the coast
throughout the globe. In addition to urbanization, population growth within the coastal zone is expected to be more
rapid than in other areas in the near future. For example,
Adger et al. (2005) calculate that more than 50 % of the
world’s population is likely to live in coastal areas by
2030. The areas affected by coastal hazards directly
depend on the topography; low-lying countries such as
the Netherlands or Bangladesh are particularly prone to
the hazards caused by rising sea levels.
Cliff collapse and other types of mass movements are
hazards when they occur close to settlements along cliff
edges (Dewez et al., 2013). Furthermore, beaches at the
base of a cliffed coastline might be used for recreational
activities (Günther and Thiel, 2009). Mass movements
occur if stability thresholds are crossed. Critical parameters are related to meteorological conditions and to tideand wave-controlled shoreface processes. Cliff collapse
is a form of episodic coastal retreat, and important parameters controlling the processes are mainly the lithology
(including water content) and structure. Frost action, in
particular the number of freeze-thaw cycles, plays an
important role in the weathering of semiconsolidated
rocks; the chalk cliffs of northern Europe is a good example of this (Duperret et al., 2002; Kuhn and Prüfer, 2014).
Bioerosion becomes an important agent, especially in the
retreat of limestone-dominated coasts within the tropics
(Vita-Finzi and Cornelius, 1973; Taboroši and Kázmér,
2013).
Despite the immediate destruction by shock waves,
earthquake-related coastal hazards are mainly attributed
to coseismic (crustal) uplift or subsidence as witnessed,
e.g., during the 1964 Alaska earthquake (Plafker, 1969).
A further criterion to distinguish coastal hazards is the
duration of time, which ranges from seconds for tsunami
landfall to thousands of years for relative sea-level
changes. Another important issue is to separate coastal
hazards into local, regional, and global hazards. All
geohazards may cause significant loss of life and may
have severe economic impacts. In the following, extreme
wave events caused by storm surges and tsunamis are
discussed.
Extreme wave events
Extreme wave events can develop into a coastal hazard,
and they primarily result from two fundamentally different
phenomena: storm surges and tsunamis. Whereas the
intensity of such events is high, the frequency is usually
low. The major difference between these two natural phenomena lies in the energy source responsible for the piling
up of water. An earthquake-generated tsunami is the result
of endogenous forces with the energy derived from the
Earth’s interior. A storm surge, however, is fueled by
exogenous forces; the energy that drives this process,
276
GEOHAZARDS: COASTAL DISASTERS
Geologic Time Scale
Marine Microfossils
Radiocarbon: Clock and Tracer
Sclerochronology
GEOHAZARDS: COASTAL DISASTERS
Gösta Hoffmann and Klaus Reicherter
Department of Geosciences and Geography, RWTH
Aachen University, Aachen, Germany
Definition
We define the term “hazard” as a potential source of harm,
where “harm” is defined as the “injury or damage to the
health of people, or damage to property or the environment” following the definition as given by ISO/IEC
(2014). The term “risk” is defined as a “combination of
the probability of occurrence of harm and the severity of
that harm” (ISO/IEC, 2014). Furthermore, the term “risk”
may be expressed as a function of hazard, exposure, and
vulnerability. A geohazard is a geological state that may
lead to widespread damage presenting severe threats to
humans, property, and the natural and built environment.
A coastal geohazard is a natural physical phenomenon
usually associated with seacoasts but to a limited extent
also along lakeshores, where the initiating process of the
disaster may originate at great distances from the point
of impact.
Introduction
There are numerous geohazards which affect coastal
regions, including beach erosion, landslide/cliff collapse,
wave attack, flooding, and tsunamis. They are always
related to the landward movement of water. These processes can be either slow or fast and may be temporary
or permanent in nature. Some hazards have meteorological causes (climatic hazards, e.g., storms, Nicholls,
2004), whereas others may be driven by Earth’s endogenous forces such as seismic events (earthquakes and tsunamis, e.g., Atwater, 1987) and volcanic eruptions (e.g.,
Firth et al., 1996). Furthermore, coastal hazards can be
gravity induced (landslide/cliff collapse, e.g., Dawson
et al., 2009; Del Río and Gracia, 2009). Relative sea-level
changes may pose a hazard to many low-lying countries as
do subsurface changes induced by humans (e.g., due to
groundwater extraction and associated settlement). As
the coastal zone is a preferred area of human settlement,
there is always some exposure to coastal hazards. Coastal
cities host many different kinds of economically relevant
infrastructure (e.g., harbors) and are often used for recreational purposes. Two percent of the world’s surface is
defined as low elevation coastal zone (LECZ).
McGranahan et al. (2007) defined the LECZ as a
contiguous area along the coast lower than 10 m above
sea-level that is inhabited by 10 % of the world’s population. Small and Nicholls (2003) estimate that around 1.2
billion people are living within 100 km of the coast
throughout the globe. In addition to urbanization, population growth within the coastal zone is expected to be more
rapid than in other areas in the near future. For example,
Adger et al. (2005) calculate that more than 50 % of the
world’s population is likely to live in coastal areas by
2030. The areas affected by coastal hazards directly
depend on the topography; low-lying countries such as
the Netherlands or Bangladesh are particularly prone to
the hazards caused by rising sea levels.
Cliff collapse and other types of mass movements are
hazards when they occur close to settlements along cliff
edges (Dewez et al., 2013). Furthermore, beaches at the
base of a cliffed coastline might be used for recreational
activities (Günther and Thiel, 2009). Mass movements
occur if stability thresholds are crossed. Critical parameters are related to meteorological conditions and to tideand wave-controlled shoreface processes. Cliff collapse
is a form of episodic coastal retreat, and important parameters controlling the processes are mainly the lithology
(including water content) and structure. Frost action, in
particular the number of freeze-thaw cycles, plays an
important role in the weathering of semiconsolidated
rocks; the chalk cliffs of northern Europe is a good example of this (Duperret et al., 2002; Kuhn and Prüfer, 2014).
Bioerosion becomes an important agent, especially in the
retreat of limestone-dominated coasts within the tropics
(Vita-Finzi and Cornelius, 1973; Taboroši and Kázmér,
2013).
Despite the immediate destruction by shock waves,
earthquake-related coastal hazards are mainly attributed
to coseismic (crustal) uplift or subsidence as witnessed,
e.g., during the 1964 Alaska earthquake (Plafker, 1969).
A further criterion to distinguish coastal hazards is the
duration of time, which ranges from seconds for tsunami
landfall to thousands of years for relative sea-level
changes. Another important issue is to separate coastal
hazards into local, regional, and global hazards. All
geohazards may cause significant loss of life and may
have severe economic impacts. In the following, extreme
wave events caused by storm surges and tsunamis are
discussed.
Extreme wave events
Extreme wave events can develop into a coastal hazard,
and they primarily result from two fundamentally different
phenomena: storm surges and tsunamis. Whereas the
intensity of such events is high, the frequency is usually
low. The major difference between these two natural phenomena lies in the energy source responsible for the piling
up of water. An earthquake-generated tsunami is the result
of endogenous forces with the energy derived from the
Earth’s interior. A storm surge, however, is fueled by
exogenous forces; the energy that drives this process,
276
GEOHAZARDS: COASTAL DISASTERS