Boulder, Colo., USA - Scores of people were killed by an explosive eruption of Kīlauea Volcano, Hawai'i, in 1790. Research presented in GSA Bulletin by D.A. Swanson of the Hawaiian Volcano Observatory and colleagues suggests that most of the fatalities were caused by hot, rapidly moving surges of volcanic debris and steam that engulfed the victims. Deposits of such surges occur on the surface on the west summit area and cover an ash bed indented with human footprints.
The footprints, made by warriors and their families, appear along a major trail in use at the time. Today, the area is one of the most visited parts of Hawai'i Volcanoes National Park.
The explosive eruption resulted from the violent interaction of groundwater with hot rocks. Such explosive eruptions have happened frequently in Kīlauea's past and will probably occur in the future when the caldera collapses down to the water table, some 600 m (2000 ft) below the summit of the volcano.
The 1790 eruption of Kīlauea was explosive, and its major impacts were in the summit area of the volcano. The eruption taking place now at Kīlauea is effusive, says Swanson, producing a flow of lava that erupts without explosion. This flow is erupting from a site named Pu'u 'Ō'ō on the east rift zone, far from the summit area, and lava has to flow many kilometers (several miles) before reaching inhabited areas.
Explosive eruptions are very hazardous; the 1790 fatalities bear witness to this fact. Lava flows are not very hazardous to life but can be exceedingly destructive to property. Explosive eruptions are brief but terrifying. Lava flows often last for months or more and are captivating to the viewer. Kīlauea has both types of eruptions, but not at the same time.
Violent explosive eruptions from the summit of Kīlauea are geologically common. They are generally clustered into periods lasting a few centuries. It has been about 200 years since the most recent major explosion, which culminated about 300 years of frequent explosive eruptions. In the past 200 years, Kīlauea has produced many lava flows similar to the present one; small explosions took place in 1924 and, on an even smaller scale, during the past 6 years.
The general public is unaware of Kīlauea's explosive nature, because the volcano has erupted mainly lava flows in recent times. Kīlauea will almost certainly become explosive at some future time, producing conditions similar to those of 1790. However, according to Swanson, there is no reason to think that a period of violent eruptions will resume any time soon. The public can probably expect more lava flows in the near future, such as those of the past three decades from Pu'u 'Ō'ō.
Reconstructing the deadly eruptive events of 1790 at Kīlauea Volcano, Hawai'i
D.A. Swanson et al., U.S. Geological Survey, Hawaiian Volcano Observatory, P.O. Box 51, Hawaii National Park, Hawaii 96718, USA. Published online ahead of print on 6 Oct. 2014; http://dx.
Other GSA BULLETIN articles (see below) cover such topics as
- 1. Geologic snapshots from the 2010 Maule earthquake region, Chile;
2. Analysis of a rapidly uplifting watershed in the San Gabriel Mountains of California (USA) that contains more than 800 waterfalls; and
3. Understanding Mars canyons through study of the Snake River Plain (USA).
GSA BULLETIN articles published ahead of print are online at http://gsabulletin.
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Constructing forearc architecture over megathrust seismic cycles: Geological snapshots from the Maule earthquake region, Chile
F. Aron et al., Dept. of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA. Published online ahead of print on 6 Oct. 2014; http://dx.
This paper presents the first neotectonic field data supporting the hypothesis that the long-term morphology and tectonics of the central-southern Chile coastal region, facing the 2010 Mw 8.8 Maule earthquake, results from extensional deformation following large subduction events accumulated over geologic time. Furthermore, the paper provides field data consistent with previous findings of other authors showing that regional-scale transverse faults, such as the Pichilemu fault, represent crustal seismogenic sources capable of producing Mw 7 shallow earthquakes. The results of this research are as well consistent with independent observations in other plate boundaries such as Japan, where large and widespread co- and post-seismic crustal faulting followed the recent, 2011 Mw 9.0 Tohoku earthquake. Seismic hazard at subduction plate boundaries not only arises from the interplate contact but also from upper plate crustal faults that may reactivate over a time period of about 10 cycles of great magnitude subduction earthquakes (Mw greater than 8.5).
The role of waterfalls and knick zones in controlling the style and pace of landscape adjustment in the western San Gabriel Mountains, California
R.A. DiBiase et al., Dept. of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA. Published online ahead of print on 22 Oct. 2014; http://dx.
Branching networks of river channels form the skeleton of mountainous landscapes, and preserve an archive of the ongoing competition between tectonic uplift and climate-driven erosion. However, in order to read the record of climate and tectonics in river profiles, a quantitative understanding of the processes that incise bedrock and transport sediment is required. One challenge is that existing models of bedrock river incision are poorly equipped to explain the growth and development of waterfalls and cascades common to landscapes experiencing a change in climate or tectonics. In this paper, we present a detailed analysis of a rapidly uplifting watershed in the San Gabriel Mountains of California containing over 800 waterfalls. We find that waterfalls and knickzones (steep river reaches) can both accelerate and slow river response to changes in uplift rate, highlighting their importance in controlling the pace of landscape evolution.
Interaction of outburst floods with basaltic aquifers on the Snake River Plain: Implications for Martian canyons
William H. Amidon and Arthur C. Clark, Middlebury College Geology Dept., Middlebury, Vermont 05753, USA. Published online ahead of print on 6 Nov. 2014; http://dx.
This paper proposes a solution to the long-standing debate about whether amphitheater-headed canyons on Mars were formed by large outburst floods or by groundwater sapping. We propose a "composite model" in which flood waters are routed through basaltic aquifers before returning to the surface and coalescing as large flows capable of significant erosion. This model may explain why many canyons on Mars lack upstream tributaries but appear too large to be formed by conventional groundwater discharges.
Mapping and measuring Lake Agassiz strandlines in North Dakota and Manitoba using LiDAR DEM data: Comparing techniques, revising correlations, and interpreting anomalous isostatic rebound gradients
James T. Teller and Zhirong Yang, Dept. of Geological Sciences, University of Manitoba, Winnipeg, MB, Canada R3T 2N2 (Teller), and Water Survey of Canada, Environment Canada, 373 Sussex Drive, Ottawa, ON, Canada K1A 0H3 (Yang). Published online ahead of print on 6 Nov. 2014; http://dx.
State-of-the art high-resolution LiDAR imagery has allowed us to map and precisely measure ancient beaches of glacial Lake Agassiz, once the largest lake in the world. This has revealed that century-long correlations of some beaches are incorrect, which is important when establishing the extent of this paleo-lake and in calculating volumes of water that periodically overflowed into the ocean and affected ocean circulation and climate; we have revised previous correlations. In addition, differential compaction of clayey deep-water sediments that lay below some of these ancient beaches, has led to deformation of the beaches, making recognition very difficult; we have revised correlations there. Our paper compares two different techniques for measuring beach elevations by LiDAR imagery, and found them comparable.
Reconstruction of maximum burial along the Northern Apennines thrust wedge (Italy) by indicators of thermal exposure and modeling
C. Caricchi et al., Dipartimento di Scienze, Sezione di Scienze Geologiche, Università "Roma Tre," Largo San Leonardo Murialdo 1, 00146 Roma, Italy. Published online ahead of print on 6 Oct. 2014; http://dx.
The paper gives an innovative contribution to understand the evolution of mountain belt (Northern Apennines case history) in terms of variations of amount and rates of shortening and tectonic transport as well as of structural style. In this research multi-method approach has adopted integrating organic and inorganic thermal indicators and thermo-chronological data as constraints for modeling. This approach substantially reduce the number of acceptable geometric and kinematic models on the basis of the amount of maximum burial and exhumation that characterize different portions of the thrust wedge. A series of thermal models, performed along five geological cross-sections across the chain, from Tyrrhenian margin to more internal sector, allowed to reconstruct the tip line of the wedge and the areal distribution of the eroded structural portion of the wedge and to trace the burial-exhumation history of the thrust belt during Tertiary times.
Insights into rates of fracture growth and sealing from a model for quartz cementation in fractured sandstones
R.H. Lander and S.E. Laubach, Geocosm, 10 Town Plaza #233, Durango, Colorado 81301 USA and Bureau of Economic Geology, The University of Texas at Austin, 10100 Burnet Road, Bldg. 130, Austin, Texas 78758 USA. Published online ahead of print on 6 Oct. 2014; http://dx.
A new model accounts for crystal growth patterns and internal textures in quartz cement in sandstone fractures as well as in metamorphic veins. The model suggests that these features form in response to (1) the ratio of the rates of quartz growth to fracture opening and (2) the substantially faster growth rate that occurs on non-euhedral surfaces in certain crystallographic orientations compared to euhedral crystal faces. In sandstones the same fundamental driving forces, in both the host rock and fracture system, are responsible for quartz cementation with the only significant difference within the fracture zone being the creation of new pore space as well as new non-euhedral surfaces for cases where overgrowths span fractures between fracturing events. Rates of fracture growth and sealing in sandstones may be inferred from fracture cement textures using model results.
Correlation of fluvial terraces and temporal steady-state incision on the onshore Makran accretionary wedge in SE Iran: Insight from channel profiles and 10Be exposure dating of strath terraces
N. Haghipour et al., Geological Institute, ETH-Zurich, Sonneggstrasse 5, CH-8092 Switzerland. Published online ahead of print on 22 Oct. 2014; http://dx.
We present local and regional incision/uplift patterns over a large area of the exposed Makran accretionary wedge. Results allow identifying regional correlations leading to robust interpretation of the landscape response to tectonic and climate changes. The measured vertical velocities can be transformed into full accretion rate, which are key to the internal dynamics of the wedge on a different time scale than denudation rates derived from low-temperature geochronology. This large-scale information is essential to characterize the bulk, natural rheology of accretionary wedges and is needed to refine numerical models of such elements of convergent plate boundaries.
Two Paleoproterozoic glacio-eustatic cycles in the Turee Creek Group, Western Australia
Martin J. Van Kranendonk and Rajat Mazumder, School of Biological, Earth and Environmental Sciences, and Australian Centre for Astrobiology, University of New South Wales, Kensington, NSW 2052, Australia. Published online ahead of print on 22 Oct. 2014; http://dx.
This study highlights climate change events associated with the rise in atmospheric oxygen 2.3 billion years ago, as preserved in a succession of rocks from Western Australia. Whereas previously only one glacial episode was known from this succession, we document two glacio-eustatic cycles from this area, each accompanied by a relative sea level fall and then rise, which aids our understanding of the extent and significance of this climatic revolution in Earth history and its influence on the evolution of the biosphere.
Characteristics of channel networks in unconfined carbonate aquifers
Stephen R.H. Worthington, Worthington Groundwater, 55 Mayfair Avenue, Dundas, Ontario L9H 3K9, Canada. Published online ahead of print on 6 Nov. 2014; http://dx.
Carbonate aquifers are some of most challenging to understand because solution can greatly enhance their permeability, but the effects of solution are often difficult to determine. This study analyzes data from caves, wells, and tracer tests to explore the extent of solution channel networks. Channels have a fractal size distribution. Caves represent the largest channels, but small channels often account for most of the permeability measured in wells. Solution channel networks are widespread in unconfined carbonate aquifers, and their presence explains why carbonate aquifers have higher permeability than aquifers in any other rock type.
Early to middle Eocene magneto-biochronology of the southwest Pacific Ocean and climate influence on sedimentation: Insights from the Mead Stream section, New Zealand
Edoardo Dallanave et al., Dept. of Earth and Environmental Science, Ludwig-Maximilians University, Theresienstrasse 41, Munich D-80333, Germany. Published online ahead of print on 6 Nov. 2014; http://dx.
In this paper we present the first magnetic polarity stratigraphy from an early-middle Eocene outcropping sedimentary record of the Southwest Pacific ocean. This record is integrated with calcareous nannofossil and foraminifera biostratigraphy. The first result is that during the early-middle Eocene the low-mid latitude calcareous nannofossil domain extended at least to ~50-55 degrees S in the South Pacific. Correlation of the magnetic polarity stratigraphy from the Mead Stream section with the geomagnetic polarity time scale allows us to derive sediment accumulation rates. Two intervals of increased sedimentation rates occurred during the early Eocene climatic optimum (52 to 50 million years ago) and during the transient warming peaking with the middle Eocene climatic optimum (40.5 million years ago). This correlation indicates that warmer climate promotes continental weathering, transportation, and accumulation of terrigenous sediments.
A way to hydrothermal paroxysm, Colli Albani Volcano, Italy
G. Vignaroli et al., Dipartimento Scienze della Terra (CNR-IGAG), Sapienza Università di Roma, Piazzale A. Moro 5, Rome, 00185, Italy. Published online ahead of print on 6 Nov. 2014; http://dx.
What causes hydrothermal paroxysm, sudden gas outburst, and similar phenomena in active volcanic settings? The Roman area in central Italy is known to be a densely-populated and volcanically-active region where numerous and dangerous hydrothermal phenomena have occurred in historical and very recent times. Even the Romans knew these phenomena, so much so that they built a drainage tunnel through the flank of the nearby Colli Albani caldera to avoid maar lake overflows during hydrothermal episodes. The main issue addressed in this work is the process leading to fluid subsurface entrapment and pressure increase up to hydro-fracturing and, possibly, to paroxysm, so to envisage such processes and mitigate their effects in the volcanically-active study area (Rome, Colli Albani) and elsewhere. The way to hydrothermal paroxysm is modulated by the pristine and transient hydraulic-rheological properties of shallow rocks. Also where permeable rocks occur initially granting the passage of hydrothermal fluids with no dangerous accumulations, the acidic hydrothermal circulation can progressively lead to a fatal argillic alteration of rocks from pervious to impervious.
A 30 Myr record of Late Triassic atmospheric pCO2 variation reflects a fundamental control of the carbon cycle by changes in continental weathering
Morgan F. Schaller et al., Dept. of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey 08854, USA, Current Address: Earth and Environmental Science, Rensselaer Polytechnic Institute, Troy, New York 12180, USA. Published online ahead of print on 6 Nov. 2014; http://dx.
We've estimated the level of CO2 in the ancient atmosphere and found that the changes that took place over a ~ 30 million year period in the late Triassic (200-230 Million years ago) are the same as those predicted by some of the most recent modeling efforts. What is really unique about this time period is that we're able to isolate many of the variables that affect atmospheric CO2 and get to the root causes of those changes. There are essentially two main drivers of CO2 concentrations over the long-term: changes in the amount coming out of the mantle, and changes in the amount removed by chemical weathering on land. What we have found is that we can ascribe much of the CO2 change in the Triassic to chemical weathering. Specifically, the amount of land area in the tropics can be a main driver of atmospheric CO2 concentrations over these long timescales.
Orogenic pulses in the Alberta Rocky Mountains: Radiometric dating of major faults and comparison with the regional tectono-stratigraphic record
D.I. Pană and B.A. van der Pluijm, Alberta Energy Regulator/Alberta Geological Survey, Twin Atria Building, 4999-98 Avenue, Edmonton, Alberta T6B 2X3, Canada (Pana), and Dept. of Earth and Environmental Sciences, University of Michigan, 1100 N. University Avenue, Ann Arbor, Michigan 48109-1005, USA (van der Pluijm). Published online ahead of print on 6 Oct. 2014; http://dx.
From the abstract: Radiometric ages from regionally distributed thrust-fault gouge show that the eastward propagation of the southern Rocky Mountain fold-and-thrust belt in Canada occurred in four orogenic pulses that correlate with tectonic events of the Cordilleran interior and with depositional patterns in the adjacent foreland. In the Main Ranges, the Pyramid (163.0 million years ago), Simpson Pass (161.7 million years ago), and Johnson Creek (145.7 million years ago) thrusts were related to the initiation of thin-skinned deformation from Jurassic terrane accretion and were partly contemporaneous with development of the first clastic wedge in the foreland basin. In the Front Ranges, the emplacement of the Greenock thrust (103.1 million years ago) and Broadview-Snake Indian thrust (99.2 million years ago) was contemporaneous with development of Cenomanian deltaic deposits in the immediate foreland. Three thrusts in the Front Ranges, Rocky Pass (74.8 million years ago), Sulfur Mountain (75.6 million years ago), and Clearwater (74.2 million years ago) thrusts, define a Campanian phase of tectonic loading that led to the last major transgression in the southern portion of the Alberta foreland. Along the eastern margin of the Front Ranges, the McConnell thrust (54.0 Ma), together with the Muskeg (52.4 million years ago), Brule (53.9 million years ago), and Nikanassin (52.1 million years ago) thrusts in the Foothills, recorded the last phase of regional contraction. The Late Jurassic, mid-Cretaceous, Late Cretaceous, and early Eocene deformation pulses are separated by relatively long periods (~45 million years, 25 million years, and 20 million years) of tectonic quiescence. These spatially and temporally restricted fault motion pulses contrast with gradual, forward fault propagation, while regional eastward progression of deformation is preserved.
High-resolution carbon isotope (delta 13Ccarb) chemostratigraphy of the lower Permian from the U.S. midcontinent: Checking the pulse of the late Paleozoic ice age
K. Tierney Cramer and M. Bostic, Dept. of Geosciences, Denison University, Granville, Ohio 43023, USA. Published online ahead of print on 22 Oct. 2014; http://dx.
From the abstract: High-resolution stable isotope chemostratigraphy from the Asselian and Sakmarian Stages (Cisuralian Series, Permian System) was carried out on the Newby 2-28R core from Stevens County, SW Kansas. The cyclothemic strata of the Council Grove and Chase Groups sampled in this study record the rapid rise and fall of sea level due to the expansion and contraction of glacial mass during the Early Permian in the waning phases of the late Paleozoic ice age... The data presented here represent the first high-resolution analysis of carbon cycle dynamics during the Early Permian, and it remains to be seen if the heartbeat of the late Paleozoic ice age preserved in this region is recognizable globally.