The following highlights summarize research papers in
Geophysical Research Letters (GL). The papers related to these
Highlights are printed in the next paper issue of the journal
following their electronic publication

1. First geophysical observations of 2002 Stromboli volcanic
collapse
2. U.S. extreme precipitation rise may be natural variability
3. Projecting future atmospheric dust reductions
4. Small elements contribute to better ocean circulation models
5. Geyser discharge likely not influenced by strain
6. Fluid injection can induce underground seismicity
7. Statistical measure of El Nino variability
8. New ocean monitor tracks seafloor fluid discharge
9. New hypothesis for Cambrian explosion
10. Prior shock likely encouraged Denali earthquake

Instruments at the Stromboli volcano in the Italian archipelago
recorded the December 2002 collapse of the island's northern flank
into the sea, which launched large tsunami waves. Bonaccorso et al.
present the first multidisciplinary data from the failure, including
thermal surveys and ground movement information from when two
portions of the volcano fell into the water. The authors report
detailed observations from the two-day sequence of events from the
start of the eruption to the collapse of a large portion of the
continually active volcano. They note that the new information will
allow researchers to interpret the conditions associated with the
flank failure, landslides, and the potential hazard of tsunamis, and
they suggest that the results can be used to refine estimates for
similar events in the future.

Title: Dynamics of the December 2002 flank failure and tsunami at
Stromboli volcano inferred by volcanological and geophysical
observations

Authors:
Alessandro Bonaccorso, S. Calvari, G. Garfi, L. Lodato, D. Patane,
National Institute of Geophysical and Volcanological Sciences,
Catania Section, Italy.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL017702, 2003

An analysis of newly available data indicates that there was a period
approximately 100 years ago when short-duration extreme
precipitation storms in the United States occurred nearly as often as
today. Kunkel et al. found a high frequency of such storms around
the turn of the 20th century, prior to the period usually associated
with manmade climate change. The authors suggest that the increase
in the frequency of intense events seen in the past 30 years could be
attributed to a combination of both natural variability and human
effects on the climate. Many existing current studies attribute the
effect to environmental changes resulting from a warmer climate.
The new report used U.S. National Weather Service precipitation
data from 1895 to the present, longer than previous data sets, and
identified a minimum in the frequency of extreme precipitation
storms during the middle of the 20th century and higher frequencies
at the start and end of the record.

Title: Temporal variations of extreme precipitation events in the
United States: 1895-2000

Authors:
Kenneth E. Kunkel, Illinois State Water Survey, Champaign,
Illinois;
David R. Easterling, NOAA/National Climatic Data Center,
Asheville, North Carolina;
Kelly Redmond, Western Regional Climate Center, Desert Research
Institute, Reno, Nevada;
Kenneth Hubbard, University of Nebraska, Lincoln, Nebraska.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL018052, 2003

Current and planned changes in land use, carbon dioxide reduction,
and human-induced climate change will likely reduce the amount of
airborne dust in the future. Mahowald and Luo studied multiple
scenarios showing possible environmental changes in the next 100
years, which suggest that climate and anthropogenic influences may
result in decreases in the atmospheric dust load ranging from 20 to
60 percent compared to current levels. Mineral aerosol levels have
varied widely in the past with human-initiated and natural climate
change and glacial cycles, which affect the amount of soil and
desert dust in the air. The authors used ice core data and previous
simulations to estimate dust sources and circulation patterns from
the late 1800s and the late 1990s and then projected the possible
results at the end of the current century. They conclude that
anticipated reductions in global dust levels have significant
implications for climate predictions and biogeochemistry in the
future.

Title: A less dusty future?

Authors:
Natalie M. Mahowald, Chao Luo, National Center for Atmospheric
Research, Boulder, Colorado.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL017880, 2003

Thin layers of water moving alternately north and south within the
thermocline (the ocean layer where the temperature starts to
decrease rapidly, about one degree Celsius [two degrees Fahrenheit]
or more with each meter [three feet] of depth) likely provide a
foundation for mixing in the Pacific Ocean, a finding that may
supply researchers with new information to refine ocean and
atmospheric models. Richards and Edwards studied the conditions
that help mix ocean water in the thermocline and found that
small-scale instabilities can enhance the likelihood of the mixing by
creating thin layers of unstable flow. They suggest that the new
information can be used to enhance ocean models, as details from
such small variations are missing from existing simulations, which
often propose colder ocean temperatures in the Pacific that extend
further west than those actually measured. The authors suggest that
ocean waters have small-scale variations, like these layers, that need
to be factored into ocean dynamics models to more accurately
portray the global ocean circulation and better estimate climate
variability.

Title: Lateral mixing in the equatorial Pacific: The importance of
inertial instability

Authors:
Kelvin J. Richards, International Pacific Research Center,
University of Hawaii, Honolulu, Hawaii;

N. R. Edwards, University of Bern, Switzerland.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL017768, 2003

New data indicate that atmospheric pressure-influenced ground
movements do not likely affect geysers and that their discharge
frequency is instead likely determined by internal dynamics.
Rojstaczer et al. monitored the Upper Geyser Basin in Yellowstone
National Park and found that Earth tides have very little influence
on hydrothermal eruptions in the region. Previous reports had
speculated that seismic activity could affect the underground strain
that governs the regular periodicity of most geysers, along with
similar phenomena like ocean-bottom discharges or volcanic
eruptions. The authors observed six strongly periodic natural
geysers in the basin, including Old Faithful, and measured the
effects from daily strains like the diurnal tides on the geyser's
eruption frequency. Their analysis suggests that only exceptionally
strong or long-period variations in the ground properties can change
the timing of a geyser's discharge.

Title: Variability in geyser eruptive timing and its causes:
Yellowstone National Park

Authors:
Stuart Rojstaczer, Duke University, Durham, North Carolina;
D. L. Galloway, U.S. Geological Survey, Sacramento, California;
S. E. Ingebritsen, U.S. Geological Survey, Menlo Park, California;
D. M. Rubin, U.S. Geological Survey, Santa Cruz, California.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL017853, 2003

Experiments in a super-deep borehole in Germany may allow
scientists to better understand the evolution of seismic activity in
the Earth's crust. Rothert et al. studied the ground movement and
liquid diffusion after injecting fluid at various depths in the
9.1 kilometer-deep [5.7 mile-deep], mostly rock borehole. Fluid
movement is associated with pressure and density changes that
often trigger earthquakes and other seismic shifts along faults. The
authors analyzed the depth and location of the epicenter from
microseismic responses after changing the ground properties by
adding fluids along pre-existing fractures. They also measured the
reflection of signals that are used to judge the intensity of seismic
activity and suggest a direct relationship between low (and high)
fluid movement and low and high signal reflection. The researchers
conclude that fluids can be used to induce underground
microseismicity.

Title: Mutual relationship between microseismicity and seismic
reflectivity: Case study at the German Continental Deep Drilling
Site (KTB)

Authors:
Elmar Rothert, S. A. Shapiro, S. Buske, Institute for Geological
Sciences, Berlin, Germany;
M. Bohnhoff, Ruhr-University Bochum, Bochum, Germany.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL017848, 2003

A statistical analysis that assesses the stability of the El Nino
weather phenomenon over the past 125 years may help climate
researchers better understand the effects of global warming on
weather. Solow and Huppert applied their new test method to more
than a century of El Nino records and found no statistically
significant evidence of a change in its variability over the past 125
years. Their investigation stems in part from a possible connection
between El Nino variability and large-scale warming; previous
researchers were concerned that large-scale global warming might
alter the evolution and movement of El Nino and disrupt weather
patterns. The authors examined records of the air pressure at sea
level and sea surface temperatures in the tropical Pacific Ocean,
both of which are influenced by El Nino, and found no change in
their behavior from the oscillation's effects.

Title: On non-stationarity of ENSO

Authors:
Andrew R. Solow, Amit Huppert, Woods Hole Oceanographic
Institution, Woods Hole, Massachusetts.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL018225, 2003

A new seafloor monitor placed in deep ocean hydrothermal
environments may reveal the possible beginnings of terrestrial life
near the planet's underwater crust. Taniguchi et al. developed an
automated water meter to measure fluid discharge that can provide
longer-term and higher-resolution measurements of water
fluctuations on the ocean floor than are currently available. The
authors placed the monitor at the base of the underwater Suiyo Sea
Mountain in Japan, where they found regular semi-daily variations
in the liquids released from the sea bottom. They then used water
temperature fluctuations at various depths to estimate the heat
transport and upward movement of the fluids. The new equipment
predicts a discharge rate into the ocean of approximately one
micrometer per second, which agrees with previous estimates.

Title: Periodical changes of submarine fluid discharge from a deep
seafloor, Suiyo Sea Mountain, Japan

Authors:
Makoto Taniguchi, Research Institute for Humanity and Nature,
Kyoto, Japan;
Shingo Uchida, Nara University of Education, Nara, Japan;
Masataka Kinoshita, Japan Marine Science and Technology Center,
Japan.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL017924, 2003

A new theory proposes that the Cambrian explosion, considered the
"big bang" of biology, when biological life rapidly flourished on
Earth, was caused when environmental conditions in the ancient
world cooled and allowed cellular life in the biosphere to begin.
Von Bloh et al. present details from their previously published Earth
system model that predicted the growth of microscopic biomass and
eventually multicellular life beginning approximately 542 million
years ago. The authors show that gradual decreases in inhospitably
warm environmental conditions passed a temperature threshold that
caused abrupt changes in the composition of the biological world.
They then describe the cooling mechanism as a trigger for the
Cambrian explosion and investigate the Earth's stability,
considering the environmental changes they proposed. The
researchers conclude that the event was most likely caused by
external factors such as continental breakup, rather than biological
growth, and agree with theories that the Earth is a self-regulating
system.

Title: Cambrian explosion triggered by geosphere-biosphere
feedbacks

Authors:
Werner von Bloh, Christin Bounama, Siegfried Franck, Postdam
Institute for Climate Impact Research, Postdam, Germany.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL017928, 2003

An earthquake in Alaska that failed to break the land surface likely
increased the ground stress and helped initiate a much stronger
quake two weeks later. Wright et al. suggest that a late October
2002 tremblor detected by satellite radar images along the Denali
Fault contributed to the adjacent 7.9 magnitude Denali earthquake
in early November that was one of the strongest ground-rupturing
quakes ever recorded. Such prior shocks are not uncommon and the
authors suggest that their results can be used to estimate the impact
of preliminary ground movement on the following quakes. The
researchers analyzed ground-sensing InSAR data between the two
events, which detected a slight shift in the ground surface caused by
slip deep within the center of the Denali fault zone. They propose
that the earthquake increased the underground stress and likely
increased the chances of the following earthquake.

Title: Source model for the Mw 6.7, 23 October 2002, Nenana
Mountain Earthquake (Alaska) from InSAR

Authors:
Tim J. Wright, Oxford University, Oxford, United Kingdom;
Zhong Lu, U.S. Geological Survey EROS Data Center, Science
Applications International Corporation, South Dakota;
Chuck Wicks, U.S. Geological Survey, Menlo Park, California.

Source: Geophysical Research Letters (GRL) paper
10.1029/2003GL018014, 2003

*****
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