scholarly journals Observations on the structure of Surtsey

2020 ◽  
Vol 14 ◽  
pp. 33-45 ◽  
Author(s):  
James C. Moore ◽  
Marie D. Jackson
Keyword(s):  
Sea Level ◽  
Explosive Activity ◽  
Geometrical Analysis ◽  
Dynamic Surface ◽  
Near Surface ◽  
Point Curve ◽  
Cast Doubt ◽  
Borehole Temperature ◽  
Water Saturated ◽  
Residual Heat

Comparison of investigations of the 1979 and 2017 cored boreholes coupled with continued observations of the dynamic surface of Surtsey has modified our concepts of the subsurface structure of the volcano. A geometrical analysis of the 2017 vertical and inclined cores indicates that near-surface layering dips westerly, indicating that the boreholes are located inside the Surtur crater. In subaerial deposits, as well as in deep deposits below sea level and below the pre-Surtsey seafloor, there are zones of porous tuff that contain abundant pyroclasts with narrow rims of fine ash. These features, typical of near-surface deposits, could have been carried down the vent by downslumping during fluctuating explosive activity. They support the hypothesis that a broad diatreme underlies the Surtur vent. No major intrusions were encountered in the 2017 drilling except for coherent basalt in deep sub-seafloor deposits below the center of Surtur crater. The 2017 borehole temperature measurements indicate that the peak temperature in the vertical boreholes was 124 °C at 105 meters below the surface (m.b.s.) and that in the inclined hole it was 127 °C at 115 m.b.s. immediately after drilling. These peak temperatures are 72 meters apart horizontally yet closely resemble each other in shape and magnitude, suggesting a broad heat source. In addition, measurements in the inclined hole from 200 to 290 m.b.s. indicate a temperature of 60±2 °C. This is apparently residual heat from the volcanic action that created the diatreme. These facts cast doubt on the previous concept that the heat anomaly in the 1979 borehole was due to a nearby intrusion. Instead they suggest that heat would have been conducted down from the 85-meter-thick hot lava shield within the Surtur crater into a warm diatreme substrate containing original volcanic heat. As the conducted heat moved down into the water-saturated substrate it would have elevated the temperature above the boiling point curve, baked out water, and created a vapor-dominated system below sea level. Eventually loss of heat by boiling and rise of steam caused the vapor-dominated system to retreat upward. The resulting steam rose and warmed the tephra adjacent to the lava shields where it produced broad areas of palagonitized tuff.

scholarly journals Increased Accumulation On The Antarctic Ice Sheet Due To Climatic Warming

1990 ◽  
Vol 14 ◽  
pp. 361-361
Author(s):  
Stephen Warren ◽  
Susan Frankenstein
Keyword(s):  
Vapor Pressure ◽  
Sea Level ◽  
Ice Sheet ◽  
Crystal Formation ◽  
Climatic Warming ◽  
Saturation Vapor Pressure ◽  
Simple Assumption ◽  
Near Surface ◽  
The Antarctic ◽  
Saturation Vapor

Climatic warming due to increased greenhouse gases is expected to cause increased precipitation in the next century because of the increased water content of the air, assuming constant relative humidity. Since temperatures over most of Antarctica are far below freezing even in the warmest month of the year, the increase in melting is probably negligible compared to the increase in precipitation.Oerlemans (1982) showed that this increase of precipitation would cause a growth of the ice sheet, tending to lower sea level. This would partially counteract the rise of sea level due to increased melting on mountain glaciers and Greenland, and to a possible (and more difficult to predict) surge of ice from West Antarctica.Oerlemans may have underestimated the increase in accumulation. He used results of General Circulation Models (GCMs) which indicated an increase of precipitation by only 12% for a temperature change ΔΤ = 3 Κ and 30% for ΔΤ = 8 K. In contrast, the change in accumulation rate at Dome C (Lorius and others, 1979) accompanying the warming from the recent ice age to the present was in accord with the simple assumption that accumulation is proportional to saturation vapor pressure at the temperature of the inversion layer, i.e. a 30% increase for ΔΤ = 3 K.The experimental results are to be preferred to the climate model results because GCMs do not represent ice-sheet accumulation processes well. Most of the accumulation is not snow falling from clouds but instead results from clear-sky ice-crystal formation in near-surface air, or hoarfrost deposition on the surface. GCMs lack sufficient vertical resolution to represent the strong temperature inversion on which these accumulation mechanisms depend.The figure shows that the increase of vapor pressure due to ΔΤ = 5 Κ varies from a factor of 1.9 at Τ = −60°C to a factor of 1.6 at Τ = −20°C. A climatic warming of 5 K. over Antarctica, which is possible during the next century, could thus increase the Antarctic accumulation from its present 17g cm−2 yr−1 to 30 g cm−2 yr−1, leading to a 50 cm drop in sea level in 100 years. This assumes that the simple proportionality of precipitation rate to saturation vapor pressure applies as well to the coastal regions, which is doubtful because the accumulation processes are not the same as on the plateau.The potential importance of Antarctic accumulation changes in contributing to changes of sea level argues for further study of the mechanisms of Antarctic precipitation and for their improved representation in climate models.

Surveying Batavia’s Graveyard: Geophysical controlled experiments and subsurface imaging of archaeological sites on an Indian Ocean coral island

Geophysics ◽  
2017 ◽  
Vol 82 (4) ◽  
pp. B147-B163 ◽  
Author(s):  
Jeffrey Shragge ◽  
David Lumley ◽  
Nader Issa ◽  
Tom Hoskin ◽  
Alistair Paterson ◽  
...  
Keyword(s):  
Sea Water ◽  
Controlled Experiments ◽  
Near Surface ◽  
Survey Techniques ◽  
Geophysical Surveys ◽  
Archaeological Materials ◽  
Coral Island ◽  
Water Saturated ◽  
Ground Penetrating ◽  
Geophysical Anomalies

We conducted geophysical surveys on Beacon Island in the Houtman Abrolhos archipelago offshore Western Australia, to investigate areas of archaeological interest related to the 1629 Batavia shipwreck, mutiny, and massacre. We used three complementary near-surface geophysical survey techniques (total magnetic intensity, electromagnetic induction mapping, and ground-penetrating radar) to identify anomalous target zones for archaeological excavation. Interpreting near-surface geophysical anomalies is often complex and nonunique, although it can be significantly improved by achieving a better understanding of site-specific factors including background conditions, natural variability, detectability limits, and the geophysical response to, and spatial resolution of, buried targets. These factors were not well-understood for Beacon Island nor indeed for the Australian coastal environment. We have evaluated the results of controlled experiments in which we bury known targets at representative depths and analyze the geophysical responses in terms of an ability to detect and resolve targets from natural background variability. The maximum depth of detectability of calibration targets on Beacon Island is limited to approximately 0.5 m due to significant variations in background physical properties between a thin ([Formula: see text]) and highly unconsolidated dry sand, shell, and coral layer of variable thickness overlying a sea-water-saturated sandy half-space. Our controlled measurements have implications for calibrating and quantifying the interpretation of geophysical anomalies in areas of archaeological interest, particularly in coastal and sandy-coral island environments. Our geophysical analyzes contributed to the discovery of archaeological materials and five historical burials associated with the 1629 Batavia shipwreck.

scholarly journals Increased Accumulation On The Antarctic Ice Sheet Due To Climatic Warming

1990 ◽  
Vol 14 ◽  
pp. 361
Author(s):  
Stephen Warren ◽  
Susan Frankenstein
Keyword(s):  
Vapor Pressure ◽  
Sea Level ◽  
Ice Sheet ◽  
Crystal Formation ◽  
Climatic Warming ◽  
Saturation Vapor Pressure ◽  
Simple Assumption ◽  
Near Surface ◽  
The Antarctic ◽  
Saturation Vapor

Climatic warming due to increased greenhouse gases is expected to cause increased precipitation in the next century because of the increased water content of the air, assuming constant relative humidity. Since temperatures over most of Antarctica are far below freezing even in the warmest month of the year, the increase in melting is probably negligible compared to the increase in precipitation. Oerlemans (1982) showed that this increase of precipitation would cause a growth of the ice sheet, tending to lower sea level. This would partially counteract the rise of sea level due to increased melting on mountain glaciers and Greenland, and to a possible (and more difficult to predict) surge of ice from West Antarctica. Oerlemans may have underestimated the increase in accumulation. He used results of General Circulation Models (GCMs) which indicated an increase of precipitation by only 12% for a temperature change ΔΤ = 3 Κ and 30% for ΔΤ = 8 K. In contrast, the change in accumulation rate at Dome C (Lorius and others, 1979) accompanying the warming from the recent ice age to the present was in accord with the simple assumption that accumulation is proportional to saturation vapor pressure at the temperature of the inversion layer, i.e. a 30% increase for ΔΤ = 3 K. The experimental results are to be preferred to the climate model results because GCMs do not represent ice-sheet accumulation processes well. Most of the accumulation is not snow falling from clouds but instead results from clear-sky ice-crystal formation in near-surface air, or hoarfrost deposition on the surface. GCMs lack sufficient vertical resolution to represent the strong temperature inversion on which these accumulation mechanisms depend. The figure shows that the increase of vapor pressure due to ΔΤ = 5 Κ varies from a factor of 1.9 at Τ = −60°C to a factor of 1.6 at Τ = −20°C. A climatic warming of 5 K. over Antarctica, which is possible during the next century, could thus increase the Antarctic accumulation from its present 17g cm−2 yr−1 to 30 g cm−2 yr−1, leading to a 50 cm drop in sea level in 100 years. This assumes that the simple proportionality of precipitation rate to saturation vapor pressure applies as well to the coastal regions, which is doubtful because the accumulation processes are not the same as on the plateau. The potential importance of Antarctic accumulation changes in contributing to changes of sea level argues for further study of the mechanisms of Antarctic precipitation and for their improved representation in climate models.

scholarly journals Water budget and partial melting in an Archean crustal column: example from the Dharwar Craton, India

2019 ◽  
Vol 489 (1) ◽  
pp. 115-133 ◽  
Author(s):  
Gautier Nicoli
Keyword(s):  
Partial Melting ◽  
Water Budget ◽  
Critical Parameter ◽  
Bound Water ◽  
Dharwar Craton ◽  
Bulk Rock ◽  
Near Surface ◽  
Surface Conditions ◽  
Magma Compositions ◽  
Water Saturated

AbstractThe fluid budget of a composite crustal column is a critical parameter that influences many lithospheric processes. The amount of water introduced into the middle and lower crust can be quantified using phase equilibrium modelling. The Dharwar Craton, India, displays a now-exposed continuous crustal section from near-surface conditions to c. 30 km depth. This section records the different steps of a c. 15 myr-long high-temperature metamorphic event (60°C kbar−1) responsible for the formation of syn- to post-tectonic anatectic intrusions. The global water budget is assessed using thermodynamic modelling on bulk-rock compositions of an average early Proterozoic supracrustal unit and c. 3.0 Ga felsic basement, the Peninsular gneisses. Results show the fast burial of a water-saturated supracrustal package (1.6 wt%) will release c. 50% of its mineral-bound water, triggering water-fluxed partial melting of the basement. Modelled anatectic magma compositions match the observed granitoid chemistries, and distinction can be made between water-fluxed melting and water-absent melting in the origin of syn- to post-tectonic anatectic granites. Findings from this study show the importance of crustal pile heterogeneity in controlling the nature of partial melting reactions, the composition of the magmas and the rheology of the crust.

scholarly journals Counteracting Climate Science Politicization With Effective Frames and Imagery

2019 ◽  
Vol 41 (2) ◽  
pp. 147-171 ◽  
Author(s):  
Toby Bolsen ◽  
Risa Palm ◽  
Justin T. Kingsland
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Visual Imagery ◽  
Climate Science ◽  
Environmental Hazards ◽  
Survey Experiment ◽  
Present Evidence ◽  
Cast Doubt ◽  
Change Beliefs

Politicization of science occurs when the inherent uncertainty of science is emphasized to cast doubt on scientific consensus. Climate change has become particularly susceptible to this kind of politicization. In this article, we report the results of a survey experiment in which we manipulated text frames and visual imagery associated with two types of environmental hazards linked to climate change—sea level rise with associated flooding and increased heat levels with associated drought and wildfires. We present evidence that the use of visual imagery can counter the effects that science politicization has on climate change beliefs and behaviors.

Observations on the Structure of Surtsey, Iceland, and its Basaltic Lapilli Tuff

2020 ◽  
Author(s):  
James G. Moore ◽  
Marie D. Jackson
Keyword(s):  
Thermal Anomaly ◽  
High Water ◽  
Unit Weight ◽  
High Porosity ◽  
The South ◽  
Dynamic Surface ◽  
Near Surface ◽  
Thin Sections ◽  
Lapilli Tuff ◽  
Comparison Of The Results

<p>Comparison of the results of new investigations of the 1979 and 2017 cored boreholes coupled with observations of the dynamic surface of Surtsey have modified our concepts of the subsurface structure of the volcano, an oceanic island erupted from 1963–1967 on the insular shelf of the south coast of Iceland. The temperature anomalies in the 2017 vertical and inclined boreholes closely resembled each other in shape and magnitude even though they are 80 m apart horizontally. The peak temperature of the vertical hole anomaly immediately after drilling was 124 °C at 105 m below surface (m.b.s.) and the inclined hole anomaly 127 °C at 115 m.b.s. This temperature anomaly and the paucity of coherent basalt in the 2017 cores casts doubt on a previous concept — that the heat anomaly in the 1979 borehole, 141 °C at 100–106 m.b.s., was due to nearby intrusions. The new observations suggest instead that top-down heating from the subaerial lava shield may have contributed to the Surtsey thermal anomaly.  In August 1966–June 1967, lava flows rapidly filled the Surtur vent crater to 80 m.b.s. and overflowed to the south and east. The conduction of heat from the cooling shield into the water-saturated substrate would have been influenced by the material characteristics of the underlying lapilli tuff, but the mechanisms of downwards heat transfer are not clear. In the zone of tidal flux centred at ~58 m.b.s., for example, the tuff was highly porous in 1979 and it remains porous and permeable 50 years after eruptions terminated. Boiling of interstitial water below sea level could have produced steam that rose and warmed the porous and permeable tephra adjacent to the lava shield, where it produced broad areas of palagonitized tuff.  Other sources of heat are also under consideration. At 107 m.b.s., fresh glass in the lapilli tuff of the original 1979 thin sections contains abundant granular and microtubular structures. These resemble endolithic microborings, and they are perhaps indicative of an early, short-lived episode of cooler temperatures and functional microbial activity at <120 °C. A geometrical analysis of layering in unrolled digital scans of the 2017 cores indicates that the relation of the apparent dip to the true dip of layering in the core inclined 55° from horizontal is such that steep dips are more common in westerly true dips, and gentle dips are more common in easterly true dips. The measurements indicate that near-surface layering in both the vertical and inclined cores dips westerly, suggesting that the boreholes are located inside the Surtur crater.  In this proximal setting, the section of lapilli tuff may be almost entirely composed of facies re-sedimented from unstable depositional sites and/or recycled through the vent perhaps multiple times. Sub-seafloor lapilli tuff samples with high porosity, high water absorption and low unit weight may reflect these complex eruptive processes. The new observations support the hypothesis that broad conduit and vent filling deposits underlie the Surtur crater.</p>

Determination of Technetium and Selenium Transport Properties in Laboratory Soil Columns

1988 ◽  
Vol 127 ◽  
Author(s):  
J. A. Del Debbio ◽  
T. R. Thomas
Keyword(s):  
Transport Properties ◽  
Soil Column ◽  
Retardation Factor ◽  
Soil Columns ◽  
Water Contact ◽  
Near Surface ◽  
One Dimensional ◽  
High Level ◽  
Water Saturated

ABSTRACTLaboratory studies are being conducted to measure the transport properties of various radionuclide species through soil columns. The studies are being conducted to support evaluations for potential near-surface disposal of high-level radioactive waste (HLW) calcine stored at the Idaho National Engineering Laboratory. The data will be used to model radionuclide transport through the vadose (unsaturated) zone of the site under various water-contact scenarios. Retardation factors and dispersion coefficients for technetium and selenium species have been measured in water-saturated soil columns made up of sediments taken from 12 and 35 meters below the surface. A one-dimensional, convective-dispersive, solute-transport equation was fitted to column effluent data by optimizing three parameters (retardation factor, dispersion coefficient and pulse time) using a non-linear, least-squares fitting routine. The data indicated no retardation of the pertechnetate ion (TcO4-)and selenate ion (SeO4-) and a large retardation of the selenite ion (SeO3-) relative to water transport through the soil column.

scholarly journals Permanent Meanders in the California Current System

2008 ◽  
Vol 38 (8) ◽  
pp. 1690-1710 ◽  
Author(s):  
L. R. Centurioni ◽  
J. C. Ohlmann ◽  
P. P. Niiler
Keyword(s):  
Sea Level ◽  
Current System ◽  
California Current ◽  
Ocean Model ◽  
Ocean Modeling ◽  
Surface Velocity ◽  
Regional Ocean Modeling System ◽  
Near Surface ◽  
Geostrophic Velocity ◽  
California Current System

Abstract Surface Velocity Program (SVP) drifter data from 1987 through 2005; Archiving, Validation, and Interpretation of Satellite Oceanographic data (AVISO) sea level anomalies; and NCEP reanalysis winds are used to assemble a time-averaged map of the 15-m-deep geostrophic velocity field in the California Current System seaward of about 50 km from the coast. The wind data are used to compute the Ekman currents, which are then subtracted from the drifter velocity measurements. The resulting proxy for geostrophic velocity anomalies computed from drifters and from satellite sea level measurements are combined to form an unbiased mean geostrophic circulation map. The result shows a California Current System that flows southward with four permanent meanders that can extend seaward for more than 800 km. Bands of alternating eastward and westward zonal currents are connected to the meanders and extend several thousand kilometers into the Pacific Ocean. This observed time-mean circulation and its associated eddy energy are compared to those produced by various high-resolution OGCM solutions: Regional Ocean Modeling System (ROMS; 5 km), Parallel Ocean Program model (POP; 1/10°), Hybrid Coordinate Ocean Model (HYCOM; 1/12°), and Naval Research Laboratory (NRL) Layered Ocean Model (NLOM; 1/32°). Simulations in closest agreement with observations come from ROMS, which also produces four meanders, geostrophic time-mean currents, and geostrophic eddy energy consistent with the observed values. The time-mean ageostrophic velocity in ROMS is strongest within the cyclonic part of the meanders and is similar to the ageostrophic velocity produced by nonlinear interaction of Ekman currents with the near-surface vorticity field.

scholarly journals Frequency dependent amplification of weak ground motions in Porirua and Lower Hutt, New Zealand

1992 ◽  
Vol 25 (4) ◽  
pp. 303-331 ◽  
Author(s):  
J. John Taber ◽  
Euan G. C. Smith
Keyword(s):  
New Zealand ◽  
Frequency Band ◽  
Spectral Ratio ◽  
Silty Sand ◽  
Peak Ground Velocity ◽  
Soft Sediment ◽  
Spectral Ratios ◽  
Near Surface ◽  
Fine Grained ◽  
Water Saturated

The relative ground response due to microearthquakes has been examined at a total of 36 sites in the Porirua and Lower Hutt regions of New Zealand, as part of a multi-disciplinary microzoning project conducted with the Wellington Regional Council. The sites were studied in two separate experiments and were chosen to sample a variety of soil types and depths ranging from strong rock to thick sections of alluvial gravels and sands to soft water-saturated fine-grained deposits. The amplitude response of each site relative to a bedrock reference site has been determined as a function of frequency. Fourier spectral ratios (Fsr) were calculated for each earthquake and then between three and twenty-six earthquakes were averaged together at each of the sites. Spectral ratios of individual earthquakes varied significantly from the average spectral ratio. In the Hutt Valley there is a gradual down-valley increase in shaking in a similar pattern to the down-valley increase of the depth to bedrock and thickness of near-surface soft sediment. The response at the upper-most valley sites, underlain by less than 50 m of alluvial gravel and silty sand, is similar to the response at the rock sites on the side of the valley (Fsr = 2.4) while the Fourier spectral ratios reach 14 at the lower-most valley sites, which are underlain by greater than 20 m of soft sediment. The highest amplifications were recorded at two sites on soft flexible sediments (10 to 35 m thick) in an enclosed valley (Fsr = 16 to 18) and a site on an apparently drained and filled swamp (Fsr = 15). A spectral ratio of 18 corresponds to an increase in peak ground velocity by a factor of 5. The amplification at most Lower Hutt sites occurred over a broad frequency band from 0.5 Hz to up to 5 Hz, with the high frequency limit of the band decreasing as the spectral ratio in the band increased. Two of the flexible sediment sites exhibited a very narrow frequency response with a peak in the 1-2 Hz range, similar to three flexible sediment sites in the Porirua basin where the amplification was in the 1-3 Hz frequency band. These flexible sediment sites had Fourier spectral ratios of up to 18 relative to a hard rock site. Three other Porirua sites had spectral ratios greater than 5 at some frequency. Two of these sites were on fan alluvium and fine grained sediment, while the third was on siltly sand on a topographic ridge. The remaining five sites were on weathered gravels and showed little amplification.

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