Physical Characteristics of Coastal Hazards 25.1 Types of Coastal Hazards 553
Part C | 25.1
duction zones. Figure 25.3 depicts the locations of the
earthquakes that generated significant tsunamis; also
marked in Fig. 25.3 are the locations of island arcs that
feature explosive volcanism.
The eruptions of Krakatau between 26th and 27th
of August 1883 generated tsunamis in the Indian
Ocean during different stages of the eruption (explosion, caldera collapse, etc. [25.26]). While the main
explosion and caldera collapse are direct ways to generate tsunamis, oftentimes associated flank collapse either
during an eruption or later, such as predicted for Cumbre Vieja Volcano (La Palma, Canary Islands, [25.27]),
can be approached by considering the slide problem.
Tsunami Source Frequency
Earthquakes occur frequently and have been recorded
for about 100 years. The distribution of earthquakes
obeys a power-law distribution, indicating that smaller
earthquakes occur more frequently than larger ones.
A similar power-law distribution can be inferred from
meteorite impact craters on the Moon and other planets [25.28, 29]. Like for earthquakes, the size distribution influences respective hazard assessment in that
smaller impacts are more frequent than larger ones. Unfortunately, there is no direct measurement and specific
distribution of submarine landslides. The main problem
with defining appropriate frequency distributions originates from the fact that submarine landslides can be
triggered not only by earthquakes, but also by sea-level
rise, excess pore pressure, weak layers, and tectonic
over-steepening of the local slope.
25.1.3 Climate Variability, Climate Change,
and Sea-Level Rise
A changing climate impacts conditions at the coast via
two main processes:
1. Changes in weather patterns, such as location and
severity, and
2. Changes in the mean sea level.
Additionally, climate varies on multiple scales.
We will only consider long-term changes; however, it
should be noted that seasonal and decadal effects are
important, for example, for determining annual periods
of storm activity, high wave energy, etc. Consequently,
even though our focus here is on secular trends, we
will include some discussion of the impact of specific
cycles.
Sea-Level Rise
Long-term changes in the climate are often associated
with global trends. Recent literature supports a global
warming trend [25.30], which in turn has implications
on processes at the coast. Eustatic, or global sea-level
rise (SLR), arises from the thermal expansion of the
ocean and ice-sheet melting. Observations of eustatic
SLR in response to global warming indicate an accelerating SLR trend [25.30–32]. Observations made in
recent years indicate that eustatic SLR has accelerated
at a rate of 3 mm=yr, with respect to an average rate of
1:7 mm=yr over the last century [25.30]. The Intergovernmental Panel on Climate Change (IPCC) [25.30],
by considering a range of future climate scenarios,
from low to high carbon emission rates resulting in
a 1.1–6:4
ı C sea-surface-temperature (SST) rise over
the next century, estimated that eustatic SLR is likely
to continue accelerating, reaching rates as high as
6:0 mm=yr when major ice-sheet melting is not considered. Literature published since the 2007 IPCC report, which considers major ice-sheet melting, largely
supports a substantially larger upper limit on eustatic
SLR projections, up to 20 mm=yr over the next century [25.33–36]. Currently, projections of eustatic SLR
over the next century range from a low of 1.8 to a high
of 20 mm=yr.
Regional influences also contribute to relative, or local, SLR at a particular location. These regional impacts
are due to processes including subsidence and tectonic
activity. The Permanent Service for Mean Sea Level reports relative sea-level trends for locations worldwide
(Table 25.1), and shows that in many locations relative SLR rates exceed the eustatic rate. For example,
the Virginia and Louisiana coasts of the United States
exhibit 30-year relative SLR rates that are 30–300%
larger than the eustatic rate; the Shanghai, China region
exhibits a 30-year relative SLR rate that is also about
300% larger than the eustatic rate.
In addition to the obvious impact of raising the
mean water level, SLR causes shoreline retreat and
land-cover changes, allows for larger waves to propagate farther inland, alters tide levels and currents, alters
storm surge magnitudes and as noted in the previous
section induces landslide-generated tsunamis [25.37–
41].
Storm Climate
Global warming trends have also been shown to impact
coastal storm activity, with the potential to alter both
storm intensity and frequency, leading to changes in
wave climate and coastal flooding. In response to the
SST rise, the coastal storm intensity and rate of occurrence is expected to change over the next century.
A number of recent studies support an increase in tropical cyclone intensity with SST rise [25.43–47], where
wind intensity is expected to increase by 2–11% over
Part C | 25.1
duction zones. Figure 25.3 depicts the locations of the
earthquakes that generated significant tsunamis; also
marked in Fig. 25.3 are the locations of island arcs that
feature explosive volcanism.
The eruptions of Krakatau between 26th and 27th
of August 1883 generated tsunamis in the Indian
Ocean during different stages of the eruption (explosion, caldera collapse, etc. [25.26]). While the main
explosion and caldera collapse are direct ways to generate tsunamis, oftentimes associated flank collapse either
during an eruption or later, such as predicted for Cumbre Vieja Volcano (La Palma, Canary Islands, [25.27]),
can be approached by considering the slide problem.
Tsunami Source Frequency
Earthquakes occur frequently and have been recorded
for about 100 years. The distribution of earthquakes
obeys a power-law distribution, indicating that smaller
earthquakes occur more frequently than larger ones.
A similar power-law distribution can be inferred from
meteorite impact craters on the Moon and other planets [25.28, 29]. Like for earthquakes, the size distribution influences respective hazard assessment in that
smaller impacts are more frequent than larger ones. Unfortunately, there is no direct measurement and specific
distribution of submarine landslides. The main problem
with defining appropriate frequency distributions originates from the fact that submarine landslides can be
triggered not only by earthquakes, but also by sea-level
rise, excess pore pressure, weak layers, and tectonic
over-steepening of the local slope.
25.1.3 Climate Variability, Climate Change,
and Sea-Level Rise
A changing climate impacts conditions at the coast via
two main processes:
1. Changes in weather patterns, such as location and
severity, and
2. Changes in the mean sea level.
Additionally, climate varies on multiple scales.
We will only consider long-term changes; however, it
should be noted that seasonal and decadal effects are
important, for example, for determining annual periods
of storm activity, high wave energy, etc. Consequently,
even though our focus here is on secular trends, we
will include some discussion of the impact of specific
cycles.
Sea-Level Rise
Long-term changes in the climate are often associated
with global trends. Recent literature supports a global
warming trend [25.30], which in turn has implications
on processes at the coast. Eustatic, or global sea-level
rise (SLR), arises from the thermal expansion of the
ocean and ice-sheet melting. Observations of eustatic
SLR in response to global warming indicate an accelerating SLR trend [25.30–32]. Observations made in
recent years indicate that eustatic SLR has accelerated
at a rate of 3 mm=yr, with respect to an average rate of
1:7 mm=yr over the last century [25.30]. The Intergovernmental Panel on Climate Change (IPCC) [25.30],
by considering a range of future climate scenarios,
from low to high carbon emission rates resulting in
a 1.1–6:4
ı C sea-surface-temperature (SST) rise over
the next century, estimated that eustatic SLR is likely
to continue accelerating, reaching rates as high as
6:0 mm=yr when major ice-sheet melting is not considered. Literature published since the 2007 IPCC report, which considers major ice-sheet melting, largely
supports a substantially larger upper limit on eustatic
SLR projections, up to 20 mm=yr over the next century [25.33–36]. Currently, projections of eustatic SLR
over the next century range from a low of 1.8 to a high
of 20 mm=yr.
Regional influences also contribute to relative, or local, SLR at a particular location. These regional impacts
are due to processes including subsidence and tectonic
activity. The Permanent Service for Mean Sea Level reports relative sea-level trends for locations worldwide
(Table 25.1), and shows that in many locations relative SLR rates exceed the eustatic rate. For example,
the Virginia and Louisiana coasts of the United States
exhibit 30-year relative SLR rates that are 30–300%
larger than the eustatic rate; the Shanghai, China region
exhibits a 30-year relative SLR rate that is also about
300% larger than the eustatic rate.
In addition to the obvious impact of raising the
mean water level, SLR causes shoreline retreat and
land-cover changes, allows for larger waves to propagate farther inland, alters tide levels and currents, alters
storm surge magnitudes and as noted in the previous
section induces landslide-generated tsunamis [25.37–
41].
Storm Climate
Global warming trends have also been shown to impact
coastal storm activity, with the potential to alter both
storm intensity and frequency, leading to changes in
wave climate and coastal flooding. In response to the
SST rise, the coastal storm intensity and rate of occurrence is expected to change over the next century.
A number of recent studies support an increase in tropical cyclone intensity with SST rise [25.43–47], where
wind intensity is expected to increase by 2–11% over