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GG Autumn Assembly
2007 |
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Chris Bochicchio |
Where did Lanikai Beach go? Determining long-term
sediment transport across the seafloor through net sediment grain-size
trend analysis
Identifying
long-term trends of sediment transport in coastal environments is a
fundamental goal shared by coastal scientists, engineers, and resource
managers. Lanikai Beach, windward Oahu, is an excellent example of
coastline where unexplained chronic beach erosion has threatened the
community. Historical photographic analysis and predictive computer models
have served as the primary approaches to characterizing long-term trends
in sediment flux. This talk presents a relatively new, geologically based
technique for characterizing littoral sediment systems, known as Net
Sediment Grain-Size Trend Analysis. This technique analyzes grain-size
data from sediment samples collected in the study area, and outputs
sediment transport vectors. This technique reveals new previously unseen
aspects of the Lanikai littoral sediment system. Net long-shore sediment
transport along Lanikai Beach is shown to be primarily to the North,
indicating a sediment deficit to the south is responsible for the observed
erosion. Northern transport agrees well with observed wind and wave data.
Results also allow the visualization of two distinct littoral cells. The
cell boundary coincides well with the area of most severe beach erosion.
Sediment thickness data of near-shore sand bodies shows the thickest
deposits in areas shown to have converging transport trends. This
technique allows for a better understanding of sediment cycling in the
coastal system, leading to a scientifically informed perspective for
coastal resource managers.
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Carrie Brugger |
Plagioclase crystallization kinetics in rhyodacite
magma during continuous decompression
experiments
Crystallization in a magma results from either a
decrease in melt temperature or volatile exsolution. Magmas in volcanic systems ascend
nearly isothermally, thus formation of microlites in volcanic conduits is
a consequence of decompression and accompanying volatile exsolution. These crystals are an important
component of magma because they help control magma viscosity and they
record valuable information about the ascent history. It has been shown that microlite
compositions and morphologies depend on the decompression path, however,
we need to understand how decompression affects kinetic processes to
interpret magma ascent processes from crystal textures in natural volcanic
rocks. In our Experimental
Petrology Laboratory we have the ability to run temperature- and
pressure-controlled experiments to simulate conditions of magma
ascent. To study the kinetics
of decompression-induced crystallization in rhyodacite magma experiments
were conducted at four decompression rates, ranging from 0.5 to 10 MPa/hr,
which correspond to ascent rates of ~0.007 to ~0.14 m/s. Two types of experiments were run:
(A) “snapshot” experiments quenched at regular intervals along each
decompression path, and (B) “anneal” experiments quenched after a long
duration at constant intermediate pressures. At the fastest decompression rate
plagioclase microlites do not begin forming until 26 MPa, significantly
below their liquidus. The
time required to reach this pressure thus represents a minimum estimate of
crystallization lag time.
Comparisons between snapshot
and anneal experiments indicate that the slowly decompressed
samples are able to crystallize an equilibrium proportion of
plagioclase until late in the decompression, thus retaining a
very low effective undercooling and remaining in the
growth-dominated crystallization regime.
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Rebecca Carey |
Dispersal characteristics of wet and dry
phases of the Askja 1875 eruption,
Iceland
The
1875 eruption of Askja volcano in
Iceland
is the youngest ‘type’
example of Phreatoplinian volcanism and the only one documented by
detailed historical reports. The main phase of the eruption began with a
dry subPlinian phase (unit B), followed by a phreatoplinian (unit C) and
finally a Plinian (unit D) phase, lasting a total of 6.5 hours.
Each phase produced a continuous tephra
sheet over eastern
Iceland
and pylograms of the
three phases each show a minimum of 3 segments, with the proximal segment
indicating significant over-thickening of these deposits irrespective of
style or intensity. In detail, there are differences in these proximal
sedimentation regimes between wet and dry fall units. The proximal
deposits of the wet phase are over-thickened at an extended distance from
vent (11 km) as compared to the Plinian phase (5.5 km). This
over-thickening must be related to the high density of the wet plume,
leading to instabilities, generating dilute weak surge deposits and/or
premature sedimentation of particles. More
than 60 active volcanoes have water- or glacier-filled summit craters or
calderas. Higher intensity phreatomagmatic eruptions have the potential to
disperse wet ash over large distances. Tephra dispersal models of tephra
from dry plumes have been well developed in recent years, however
dispersal models of wet plumes need to be better
quantified. |
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Tom Fedenczuk |
Quantitative
characterization of topographical features in digital elevation models
(DEM) and bathymetry data
We
have developed an automated and quantitative approach to the
interpretation of topographical features with an application to EM300
bathymetry data collected in 2003 over Big Blue Seamount, a serpentinite
mud volcano in the Mariana forearc region (Western Pacific). The method
employs a series of Matrix
Laboratory (MATLAB)
functions and scripts, and exports the results as data sets, figures, text
files, and summary reports. These can be visualized and manipulated in
MATLAB itself or in Geographic
Information System (GIS)
applications. The method can be used for any digital
topographic/bathymetric data set in subaerial or submarine settings to
characterize surface features such as flows, folds, distal edges of flows
or mass-wasting deposits, slump scars, fault scarps, ridges, valleys, and
plateaus. It provides a method for analyzing surface roughness as well as
gradient magnitude and direction. It is automated to convert DEM and
bathymetry into gradient datasets, render gradient maps, create profiles
across morphologic features, determine the underlying slope of the
features, calculate the slope-corrected heights (or thickness), and
estimate volumes by assuming that thickness satisfies Laplace’s
equation. This approach
permits a more rigorous measure of surface morphology that can be applied
to the interpretation of a wide variety of geologic settings, ranging from
volcanic and mass-wasting processes to reef
habitats. |
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Pat Hughes |
Tracking the mobility of subsurface oil plumes using a
fluorescent tracer
Portions of the Honolulu Harbor area have hosted industrial
activities for the last 100+ years. During that time, petroleum
operations associated with these activities have resulted in numerous
releases of oil into the subsurface. One particular 20 acre parcel – the
setting for this talk - is underlain by an oil plume, estimated to be some
2.5 million liters in volume. One of the key questions at this site is
whether or not the oil plume is mobile or stable. If it is still mobile -
and therefore still moving toward the Harbor – then relatively more
aggressive actions need to be taken to contain the plume. On the other
hand, if the oil plume has stabilized, then relatively less aggressive
actions may be sufficient, to slowly recover and manage the oil plume in
place. Typically a combination of monitoring and numerical modeling is
used to answer this sort of question. Both techniques, however, involve
indirect measurement of the
mobility of the oil plume.
Recently a new technique was developed to directly measure the movement of
these plumes, using a fluorescent tracer. As originally envisioned, the
technique was not expected to be applicable in coastal settings, where
tidal fluctuations might affect the results. This talk will briefly
discuss the basic tracer technique, and then describe the efforts to adapt
the technique, for use in a tidal setting.
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Seung-Sep
Kim |
Effects of uncertainties in surface load on estimation of
elastic thickness
Estimated elastic thicknesses of the lithosphere beneath
volcanic edifices reflect the thermal age of the lithosphere at the time
of loading. Because no
“perfect” observation and prediction are available in reality, those
estimated values are normally constrained by lower and upper limits in
order to comprehend errors in both observed data and model. However, a criterion to determine
such limits has not been established. Even if one finds that errors in
observed data are purely random and a model approximates the data well,
uncertainties related to hidden surface loads still need to be
investigated. Because
bathymetry is the combination of numerous nonlinear geologic processes,
including both lithospheric cooling and swells, it is necessary for
flexure modeling to separate volcanic surface loads (i.e., seamounts) from
the rest of observed data not directly associated with flexural
deformation. Unfortunately,
this separation can only be approximate, not exact, so that some
uncertainties in the description of the surface loading are
unavoidable. Thus, I explore their behaviors in simple flexure models using (1)
synthetic data and (2) real geophysical data in the vicinity of theCape
Verde
Islands. Directional median (DiM) filtering
is employed to separate the Island loads from the
Cape Verde
swell and its uncertainties are measured in terms of the median absolute
deviation (MAD) values that reflect the sensitivity to the solutions as we
vary the DiM filter widths. |
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Eric Mittelstaedt |
Ridge jumps associated with
plume-ridge interaction: Weakening of the lithosphere by upwelling
asthenosphere
Interaction
of mantle plumes and young lithosphere near mid-ocean ridges can lead to
changes in spreading geometry by shifts of the ridge-axis toward the plume
such as seen at
Iceland
and the Galapagos. Previous work has shown that, with
a sufficient magma flux, magmatism alone may weaken the plate sufficiently
to initiate a ridge jump, but the contribution of upwelling asthenosphere
to plate weakening and ridge-jumps is poorly understood. Using the FLAC
(Fast Lagrangian Analysis of Continua) algorithm, we solve the equations
of continuity, momentum and energy to examine deformation in near-ridge
lithosphere associated with relatively hot upwelling asthenosphere and
seafloor spreading. The cold portion of the lithosphere is treated as an
elastic-plastic material and experiences brittle failure while the lower
lithosphere and asthenosphere obey a non-Newtonian viscous rheology.
Combined with a freely deformable surface this allows for simulation of
gravitational effects on topography and dynamic faulting. The upper region
of the box is initially set to a square-root of age thermal profile while
a hot patch is placed at the bottom to initiate a single asthenospheric
upwelling. The effect of upwelling asthenosphere on ridge jumps is
evaluated by varying three parameters; the plume excess temperature, the
spreading rate and the lateral location of the hot patch relative to the
ridge axis. Preliminary results show plume related thinning (i.e.
weakening) of the lithosphere over a wide area (100’s of km’s) with the
rate of thinning dependent upon the thermal excess temperature of the
plume. Initially thinning occurs as the plume approaches the lithosphere
and asthenospheric material is forced out of the way. As the plume
material comes into contact with the lithosphere, thinning of the boundary
layer occurs through thermal weakening and mechanical removal of material.
Thinning of the lithosphere is one of two primary factors in achieving a
ridge jump. The other is high stresses capable of initiating rifting at
this weakened location. Model stresses induced by the buoyant
asthenosphere are significant fractions of the lithospheric yield strength
near the plume and reach a maximum at the center of plume upwelling. The
stresses decrease with distance from the plume center and increase with
increasing spreading rate. Ridge jumps induced by upwelling asthenosphere
alone are not observed which suggests that additional effects, such as
off-axis magmatism, are important to ridge jump
formation.
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Eva-Marie Nosal |
Bottom-mounted hydrophones used to investigate sperm whale
swim orientation and click characteristics
Located in the Tongue of the
Ocean in the Bahamas, the U.S. Navy's Atlantic Undersea Test and
Evaluation Center (AUTEC) includes a sophisticated array of bottom-mounted
widely-spaced (~10 km spacing) hydrophones. Data collected on the AUTEC
array is often rich with marine mammal vocalizations, making it a valuable
resource for the development of tracking methods and for marine mammal
studies. We developed a sperm whale tracking algorithm and applied it to
25 minutes of data recorded on 5 AUTEC phones. Our method relies on
arrival times of direct and surface-reflected paths and gives position
estimates that are accurate to within 10 meters. With such accuracy, we
were able to estimate the whale's pitch and yaw by assuming that its main
axis (which points from the tail to the rostrum) is parallel to its
velocity. Roll was found by fitting the details of the pulses within each
sperm whale click to the so-called bent horn model of sperm whale sound
production. Given the position and orientation of the whale, we
reconstructed its beam pattern, which was found to be highly directional
with an intense forward directed component. [Work supported by the Office
of Naval Research. Data provided by the Naval Undersea Warfare Center].
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Brad Romine |
Overview of the PX and
PXT shoreline change rate methods and results from the s outheast Oahu
shoreline study
Coastal
erosion studies by the University of Hawaii Coastal
Geology Group provide technical
information on shoreline dynamics to help government agencies and the
public manage coastal resources and avoid coastal hazards. To further the
goal of providing reliable erosion study results, we developed the PX and
PXT methods for calculating shoreline erosion rates, which employ
polynomial regression to model shoreline change using historical shoreline
data from an entire beach.
These methods are an improvement on the previously used single
transect (ST) method as they produce more statistically significant and
defensible erosion rates.
I present a comparison
of the PX, PXT, and ST methods for shoreline change rate calculation,
along with results from shoreline change analysis using these methods for
several beaches on southeast Oahu. |
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Kolja Rotzoll |
Numerical ground-water flow
simulation around Red Hill Ridge, Oahu, Hawaii
The Red Hill Fuel Storage Facility (RHFSF),
located on south
Oahu, consists of 20
underground storage tanks with a total capacity of about 250 million
gallons of petroleum-based fuel. Several public drinking-water sources are
located down gradient from the fuel tanks. A numerical ground-water flow
model was developed to simulate the flow around the RHFSF. The
three-dimensional MODFLOW model is comprised of seven layers including
Koolau basalt, caprock, and low-permeability valley-fills. The model was
calibrated with the island-wide Source Water Assessment Program model and
an 18-day aquifer test with nine observations wells across the adjacent
valleys. The calibration of the transient model was good, except for over
predicting the responses north of the Halawa valley fill from pumping Red
Hill Shaft. Capture zone delineation indicates that ground-water flow
passing the fuel tanks is withdrawn at Red Hill Shaft, which poses a
potential risk to human health associated with petroleum compounds from
past or future releases to the environment from the RHFSF. The model is
acceptable as a tool to evaluate the transport of actual or hypothetical
dissolved petroleum constituents in the ground water under a variety of
pumping and recharge
conditions.
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Andrea Steffke |
Coupled use of COSPEC and satellite measurements to
define volumetric balance during effusive eruptions at Mt.
Etna, Italy
Sulfur
dioxide (SO2) fluxes have been derived from COSPEC measurements gathered
at Mt. Etna,
Italy, on a
regular basis since 1987. SO2 fluxes are used to calculate volumes of
degassed magma that are in turn used to calculate magma supply rates and
related volumes. At the same time, satellite thermal data can be used to
estimate effusion rates and erupted volumes. In this study we compare the
volumes of degassed magma with the amount of erupted lava during three
eruptions at Mt. Etna between 2002 and 2006. We use COSPEC
derived SO2 fluxes to calculate the volume of degassed magma and Advanced
Very High Resolution (AVHRR) thermal satellite data to measure the volume
of erupted lava. Both methods have associated errors of approximately 30
percent. We observed three types of behavior during these eruptions: Type
1 - degassed magma is less than erupted volume. This implies that a
portion of the erupted volume comprised magma that was previously
degassed, possibly in storage. Type 2 - degassed magma is equal to erupted
volume. In this case degassed magma is erupted to produce lava flows. Type
3 - degassed magma is greater than erupted magma. A portion of degassed
magma was not erupted, was degassed within the conduits feeding
coincident, persistent (non-effusive) degassing activity at the summit
craters, and/or some of the degassed volume was represented by ash. We
show that the balance between the volumes of degassed magma and erupted
lava not only varies from eruption to eruption, but also varies during
single
eruptions.
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Wendy Stovall |
Density-driven crustal
overturn in l
ava l
akes: The example of
Kilauea Iki
1959
Lava lakes are common features at basaltic volcanoes on
Earth and other planetary bodies including Triton and Io and the motion of
crustal surface plates has been used as an analog to global plate
tectonics. Previous studies have attributed crustal foundering and
accompanying crustal motion to thermal and/or density differences within
the lava. However at active lava lakes, i.e. those fed by a vent directly
below the lake, the overturn process proceeds to completion leaving no
physical evidence of the foundering event and hence limiting our ability
to constrain inputs into models of the process. In addition the close of
eruptive activity is generally accompanied by magma withdrawal and lake
surface collapse, thereby destroying surface crust features associated
with overturn. In contrast inactive lava lakes (fed by vents adjacent to
the lake) typically have shorter lifetimes of active overturn, limited
lava withdrawal and therefore significantly higher preservation potential
for surface features associated with crustal motion. As an example, part
of the surface of the 1959 Kilauea Iki lava lake in
Hawai’i
preserves the
‘frozen’ record of a final, incomplete crustal-overturn cycle
enabling us to sample portions of foundering crust plus
over-riding and under-lying lava to constrain the density of
the units involved in the overturn process. This evidence
indicates a significant density difference driving crustal
foundering, leading inevitably to complete crustal
renewal. |
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Loyc
Vanderkluysen |
Dike of the Deccan
Traps: Insights into the plumbing system of a continental flood basalt
province
The difficulty in
identifying and locating vent areas in the Deccan Traps of India remains a
barrier to our understanding of the emplacement of this 500,000
km2
continental flood basalt province. Spatial, temporal and tectonic
information recorded by feeder dikes are thus a key component in our study
of the emplacement of the province. Our study, focusing on the major and trace element
and Pb, Sr, and Nd isotope characteristics of samples from all three dike
swarms identified in the province, reveals that dikes with isotopic and
chemical signatures matching those of the upper group of lava formations
are abundant in the west coast swarm and the central Nasik-Pune swarm,
whereas a number of feeders for the lower and middle formations are
located in northern Narmada-Tapi swarm. As a group, the feeder-like dikes
for the upper formations in the coastal and Nasik-Pune swarms do not
display any preferred trend, precluding rifting to have been dominant at
the time of their emplacement. Dikes with signatures matching those of the
lower and middle formations found in the Narmada-Tapi swarm, however, have
geometries indicating that N-S extension was taking place in the area at
the time. On this basis, we propose that rifting was occurring in the
Narmada-Tapi region in the earlier phases of the mainDeccan volcanic event, but did not affect the feeder
swarms of the upper formations. E-W extension along the west coast
followed shortly after the emplacement of the Deccan’s upper formations. As a
result, N-S rifting in the Narmada-Tapi region cannot be ruled out as a
trigger mechanism for the massive melting event, whereas E-W extension
along the coast can be excluded. |
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Sean Vitousek |
Conicidence of high wave and high tide events:
Implications for wave runup and the influence of sea-level
rise
Inundation water levels and coastal erosion are a function
of both wave height and tide. Wave events occurring on high (spring) tides
cause significant erosion and inundation; where as, wave events falling on
low (neap) tides often do not. Joint probability models of high wave and
high tide events are constructed from observations. Empirical runup
equations translate wave height into wave runup and allow for construction
of joint probability models of wave runup and tide. An individual
probability distribution of total inundation water level can be
constructed from the sum of the wave runup and tide probabilities. The
influence of sea-level rise on frequency of inundation is explored using
total inundation water level probability distributions. The increase in
inundation frequency for general areas is found to be about 1.3% per year.
A case study for Laniakea on the North Shore of Oahu, Hawai‘i is also
considered. The highway at Laniakea is overtopped by large wave events and
shut down a few times per year. A sea-level rise scenario of +0.5 m will
drastically increase the frequency of highway
inundation. |
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Bob Whittier |
Oxygen
and hydrogen isotope anomalies: The implication for the water
budget
The
hydrogen and oxygen isotopic composition of stream and groundwater is
dependent on the isotopic composition of the precipitation, and
evaporation during and after the precipitation events. Precipitation generally gets
trends toward a lighter isotopic composition as elevation increases and as
temperature decreases. The
elevation effects are further amplified by higher elevations having a
higher ratio of snow (which is isotopically light) to rain (which is
isotopically heavy) compared to the lower elevation precipitation. In a high elevation basin in
East-Central
Idaho, the relationship was
reversed where the highest elevation water sampled also had the heaviest
isotopic composition. The
current research, which is studying the groundwater/surface water
interaction in this basin, will investigate if this anomaly indicates a
shorter residence time for water in high mountain area resulting in a
greater contribution of rain versus snow to the summer baseflow. Further analysis will
investigate if this anomaly indicates that the precipitation is currently
underestimated in the high mountain areas of the
basin.
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