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The Geological Triggers of Climate Change
Climate Forcing of Geological Hazards.
Bill McGuire and Mark A. Maslin, eds.
Wiley, 2013. 326 pp., illus. $159.95
(ISBN 9780470658659 cloth).
I
n the Pacific Northwest, where I
live, we have witnessed geologic hazards triggered by climate change. In
November 2006, a heavy rainstorm
created debris flows, a watery mixture
of sediment and boulders, on several
of our glacier-clad volcanoes—most
notably, Mount Hood (just outside of
Portland, Oregon) and Mount Rainier
(southeast of Seattle, Washington). The
debris flows were initiated in glacial
valleys, where the steep valley walls are
no longer buttressed by the presence of
glacial ice. One consequence of these
flows was the closure of a major highway on the east side of Mount Hood
for about a month, isolating a major
ski area. In Mount Rainier National
Park, one road was closed for over
a year. With this background, I read
Climate Forcing of Geological Hazards
with more than just academic interest.
The edited volume is geological and
geophysical in nature, covering volcanic eruptions, faults, landslides, and
methane hydrates in 12 chapters. It does
not cover the more geomorphology-­
oriented processes, such as debris
flows, riverine environments, or coastal
shorelines, that might be of more
direct interest to biologists. However,
to understand the long-term (approximately 103 years) trends of geological
hazards, this book is a helpful guide.
The first two chapters serve as an
introduction, providing an overview of
the material and a pro forma summary
of climate projections through the end
of this century. The first chapter argues
that geologic conditions on the threshold of stability can be destabilized by
relatively small changes in mass distribution (relative to the mass of the
rock overburden) in climate-affected
landscapes, such as the mass of snow
and ice or sea-level change.
68 BioScience • January 2014 / Vol. 64 No. 1
The next three chapters offer details
of geological hazards and focus on
volcanic events. Mount Etna, in Sicily,
is used as a case study about processes
that trigger edifice collapses. Much
text is devoted to the dating of an
ancient edifice collapse, which may
be more appropriate for a book on
dating techniques, and then attempts
to link the timing of the collapse to a
wet climatic period, suggesting that the
increased infiltration of water into the
volcano walls weakened its mechanical strength. The implication is that
if glacier-clad volcanoes are subject
to increased ice melt caused by climate warming, they, too, would be less
stable.
The next chapter tries to link volcanic eruptions to shrinking glaciers,
the notion being that, as the weight
of the ice decreases, the magma vents
more easily, and eruptions increase
in frequency. Although I am sympathetic to the argument, I think that it
is a stretch. The eruptive frequency of
volcanoes has not changed over the
past 1000 years, which brackets the
Little Ice Age, the most glaciologically
significant event in the past several
thousand years—and a period rich
in dated samples. If such a volcanic
response exists, the response time is
much slower than the variation in the
climate (around 102 years).
In contrast to the implication in the
previous chapter, the following chapter
suggests that volcanic activity may be
reduced by the shrinking of glaciers. As
pressure on the planet’s crust decreases
as a result of ice loss, the volume of
shallow magmatic chambers increases
because of the elastic rebound of the
crust; together with fractures created
by the rebound, this increased volume
reduces the local magmatic pressure.
Although the loss of ice may
not have a decisive effect on eruptive activity, faulting behavior may
be a different story. Both terrestrial
and marine fault environments are
examined, as are the specific faults in
three regions: northern Scandinavia,
Utah, and Wyoming. The loading or
unloading of the crust changes the
pattern of stress accumulation, which
causes fault slip. Numerical modeling
shows that crustal unloading, due to
the disappearance of Pleistocene glaciers and lakes, can cause fault slip and
may explain the synchronous increase
in postglacial seismicity observed in
regions formerly covered by glaciers
and ice sheets.
Climate Forcing of Geological Hazards
next examines whether the relatively
small variations in sea level (40 centimeters) due to the El Nino–Southern
Oscillation (ENSO) can affect seismicity along the plate boundary at the East
Pacific Rise in the southeastern Pacific
Ocean, which is highly fractured and
relatively weak. Results show a significant correlation between seismic
events and the Southern Oscillation
Index, and seismic activity is greatest several months after an ENSOinduced lower sea level. Although no
direct connections to geologic hazards exist, such changes may help
trigger large earthquakes by concentrating stress in faults in a more critical
state.
Two subsequent chapters address
the possible effects of climate change
on landslide potential. The first reports
on different styles of continental shelf
landslides, their global distribution,
and their geomorphic setting. Potential
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landslides exist where thick deposits
of stable coarse sediments, deposited
during glacial periods, are separated
(interbedded) by weak, fine-grained
sediments deposited during interglacial periods. The second of these
two chapters examines landslides in
high-mountain regions related to ice
and changing meteorological conditions. On the basis of studies in three
different regions—­central Alaska, the
European Alps, and the Southern Alps
of New Zealand—two general (and
separate) associations emerge. The first
is a period (days) of warm weather
prior to a landslide, and the second
is a sudden drop in air temperature
to below freezing in the hours (to
days) before the event. The hypothesis
for the former is that meltwater from
snow and ice fills the fractures in the
rock, reducing the rock strength; for
the l­atter, the freezing of infiltrated
meltwater mechanically weakens the
­
rock.
The book concludes with a wonderful overview of hydrates, including
the history of their discovery (natural
deposits were not recognized until the
1970s), their crystalline structure, their
role in recent geologic history, and
the potential hazards that are associated with them. These ice-like deposits
of gas—mostly methane—are stable
under high pressure and at low temperatures and are found at the ocean
bottom and in permafrost. Were the
ocean to warm sufficiently, the clathrate would break down and release
methane, a greenhouse gas, which
would contribute to accelerated global
warming. Thawing hydrate ice may
also trigger underwater landslides that
could release other methane deposits
or even create tsunamis. Identifying
the distribution of hydrate deposits
and keeping an eye on their stability is
in our best interest.
Climate Forcing of Geological
Hazards thoroughly addresses the
­volcanic eruptions and landslides that
are associated with climate warming.
Its informative material will teach
even those readers, such as myself,
who think they know the subject
matter.
http://bioscience.oxfordjournals.org ANDREW G. FOUNTAIN
Andrew G. Fountain ([email protected])
is a professor of geography and geology
at Portland State University,
in Portland, Oregon.
doi:10.1093/biosci/bit011
TIME AND TIDE
Rising Seas: Past, Present, Future.
Vivien Gornitz. Columbia University
Press, 2013. 360 pp., illus. $40.00 (ISBN
9780231147392 paper).
T
he specter of sea-level rise is one of
the most charismatic consequences
of climate change. It is also the subject
that is covered admirably, and with
an overarching historical context, by
Vivien Gornitz in her book Rising
Seas: Past, Present, Future. Gornitz
has made sea-level studies a focus of
her career at the Columbia University
Center for Climate Systems Research
and the NASA Goddard Institute for
Space Studies, and her (1982) article in
Science helped usher in the modern era
of sea-level-rise research.
To understand the movement and the
levels of the seas is to gain insight into
how the Earth has functioned throughout history. Sea-level change is mostly
associated these days with climate
change. Rising temperatures are melting glaciers and heating seawater—and
increasing the volume of the oceans.
Gornitz argues that the factors controlling this warming process are now more
numerous than at any other point during human history. At any given time,
the levels of the oceans are controlled
astronomically: The relative positions
of the Earth, the Moon, and the Sun
are the principal factors controlling the
tides. Indeed, these daily fluctuations
are the aspects of sea-level change most
commonly experienced. Over much
longer time scales, however, the position
of the sea is controlled by the tectonic
movement of the Earth’s plates, because
the rate of seafloor spreading controls
an ocean’s temperature and also the
buoyancy of those plates. Periods of
fast seafloor spreading, such as during
the Cretaceous Period, tended to have
a buoyant ocean crust and, therefore,
higher sea levels, whereas the modern
Quaternary Period has a slower rate of
seafloor spreading and generally lower
sea levels.
Sea level is also controlled by
changes in the mass and density of
the lithosphere with respect to underlying the asthenosphere, a process of
equilibrium called isostacy. In many
places in North America and Europe,
glacially driven isostatic adjustments
are one of the major factors influencing sea-level change over the past
several thousand years. In locations
with soft sediments, such as deltas,
sea-level rise is affected by sediment
autocompaction, sediment dewatering, and oil and gas production.
Rising Seas is written for a wide
audience—an academic who is not an
expert on the subject but who wishes
to learn more or a layman interested
in the long-term effects of sea-level
rise. The book is enjoyable to read,
thoughtfully illustrated and ­containing
artful renderings of climatic processes and presentations of raw data.
Schematics are found throughout the
pages that explain important sea-levelrelated processes, such as how isostacy
functions, how a tide gauge works, and
how sand is transported along a beach.
In addition, there are data that present
temperature changes in ice cores, as
well as tide gauge and altimetry data of
sea-level change over the past century
and a half.
January 2014 / Vol. 64 No. 1 • BioScience 69