Haraldur Sigurdsson | University of Rhode Island (original) (raw)

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Papers by Haraldur Sigurdsson

Ground-penetrating radar (GPR) is used to image and characterize fall and pyroclastic flow deposi... more Ground-penetrating radar (GPR) is used to image and characterize fall and pyroclastic flow deposits from the 1815 eruption of Tambora volcano in Indonesia. Analysis of GPR common-mid-point (CMP) data indicate that the velocity of radar in the subsurface is 0.1 m/ns, and this is used to establish a preliminary traveltime to-depth conversion for common-offset reflection profiles. Common-offset radar profiles were collected along the edge of an erosional gully that exposed approximately 1-2 m of volcanic stratigraphy. Additional trenching at select locations in the gully exposed the contact between the pre-1815 eruption surface and overlying pyroclastic deposit from the 1815 eruption. The deepest continuous, prominent reflection is shown to correspond to the interface between pre-eruption clay-rich soil and pyroclastics that reach a maximum thickness of 4 m along our profiles. This soil surface is distinctly terraced and is interpreted as the ground surface augmented for agriculture and buildings by people from the kingdom of Tambora. The correlation of volcanic stratigraphy and radar data at this location indicates that reflections are produced by the soil-pyroclastic deposit interface and the interface between pyroclastic flows (including pyroclastic surge) and the pumicerich fall deposits. In the thickest deposits an additional reflection marks the interface between two pyroclastic flow units.

Geochimica et Cosmochimica Acta, 2019

Multibeam bathymetry mapping and seismic airgun surveys of the submarine region around the Santor... more Multibeam bathymetry mapping and seismic airgun surveys of the submarine region around the Santorini volcanic field in the Hellenic Arc (Greece) have revealed regions of terraced or step-like topography. These features may be related to the transport and deposition of submarine pyroclastic flows from the last major eruption of this volcano (~3600yrs. B.P.). The uppermost sediment sequence identified in seismic

Drilling in the Caribbean Sea during Ocean Drilling Program Leg 165 has recovered a large number ... more Drilling in the Caribbean Sea during Ocean Drilling Program Leg 165 has recovered a large number of silicic tephra layers and led to the discovery of three major episodes of explosive volcanism that occurred during the last 55 m.y. on the margins of this evolving ocean basin. The earliest episode is marked by Paleocene to early Eocene explosive volcanism on the Cayman Rise, associated with activity of the Cayman arc, an island arc that was the westward extension of the Sierra Maestra volcanic arc in southern Cuba. Caribbean sediments also document a major mid- to late Eocene explosive volcanic episode that is attributed to ignimbrite-forming eruptions on the Chortis Block in Central America to the west. This event is contemporaneous with the first phase of activity of the Sierra Madre volcanic episode in Mexico, the largest ignimbrite province on Earth. In the Caribbean sediments, a Miocene episode of explosive volcanism is comparable to the Eocene event, and also attributed to sources in the Central American arc to the west. Radiometric 40Ar/39Ar dates have been obtained for biotites and sanidines from 27 tephra layers, providing absolute ages for the volcanic episodes and further constraining the geochronology of Caribbean sediments. Volcanic activity of the Cayman arc is attributed to the northward subduction of the leading edge of the oceanic plate that carried the Caribbean oceanic plateau. Although the factors generating the large episodes of Central American explosive volcanism are unclear, we propose that they are related to contemporary major readjustments of plate tectonic configuration in the Pacific.

Proceedings of the Ocean Drilling Program, 1997

The Cretaceous-Tertiary Event and Other Catastrophes in Earth History, 1996

ABSTRACT Tektite glasses from Beloc, Haiti, formed by impact melting, show bimodal composition of... more ABSTRACT Tektite glasses from Beloc, Haiti, formed by impact melting, show bimodal composition of doininantly silicic melt of crustal origin (black glass) and a minor CaO-rich melt of sedimentary origin (yellow glass). Low-velocity Mossbauer spectra of the black ...

Initial Reports of the Deep Sea Drilling Project, 1977

Indonesian Journal on Geoscience, 2006

The eruption of Tambora volcano on the island of Sumbawa in 1815 is generally considered as the l... more The eruption of Tambora volcano on the island of Sumbawa in 1815 is generally considered as the largest and the most violent volcanic event in recorded history. The cataclysmic eruption occurred on 11 April 1815 was initiated by Plinian eruption type on 5 April and killed more than 90,000 people on Sumbawa and nearby Lombok. The type plinian eruptions occurred twice and ejected gray pumice and ash, to form stratified deposits as thick as 40-150 cm on the slopes and mostly distributed over the district west of the volcano. Following this, at about 7 pm, on 11 April the first pyroclastic surge was generated and progressively became greater extending to almost whole direction, mainly to the north, west, and south districts from the eruption center. The deadliest volcanic eruption buried ancient villages by pyroclastic surge and flow deposits in almost intact state, thus preserving important archaeological evidence for the period. High preservation in relatively stable conditions and known date of the eruptions provide approximate dating for the archaeological remains. Archaeological excavations on the site uncovered a variety of remains were relieved by ground penetrating radar (GPR) to map structural remains of the ancient villages under the pyroclastic surge and flow deposits. These traverses showed that GPR could define structures as deep as 10 m (velocity 0.090 m/ns) and could accurately map the thickness of the stratified volcanic deposits in the Tambora village area.

Journal of Volcanology and Geothermal Research, 1982

A theoretical analysis is presented for the spread of a viscous liquid flowing under its own hydr... more A theoretical analysis is presented for the spread of a viscous liquid flowing under its own hydrostatic pressure on a horizontal surface in order to model lava dome formation. Two situations are considered in detail: the spreading of a constant volume of liquid and the case where the amount of liquid is continually increased. Experiments with silicone liquids show close agreement with theory. The formation of a basaltic andesite lava extrusion in 1979 on the crater floor of the Soufri~re of St. Vincent (West Indies) provided the motivation for and an application of the model. The extrusion reached a diameter of 868 m and a height of 133 m over a period of 150 days. Over the first 90 days the growth relationships were consistent with those predicted by theory. Application of the theory to the Soufri~re dome suggests an effective viscosity of 2 × 1012 poise for the basaltic andesite lava. The large effective viscosity calculated for the lava may be attributed to the dominant influence of a high-viscosity skin which forms at the margins of the flow as it cools. After 70 days, the rate of growth of the extrusion markedly decreased because a substantial collar of rubble accumulated at the flow front. Due to this collar the growth of the extrusion ceased after 150 days. From approximately two weeks after the initiation of the extrusion, the discharge rate of lava decreased approximately tineariy with increasing dome height. This observation suggests that the lava ascended under a decreasing hydrostatic driving pressure and that extrusion ceased when the lava column reached hydrostatic equilibrium.

AGUFM, Dec 1, 2006

Subduction zone magmas are typically characterized by high concentrations of dissolved H2O (up to... more Subduction zone magmas are typically characterized by high concentrations of dissolved H2O (up to 6-7 wt%), presumably derived from the subducted plate and ultimately responsible for melt generation in this tectonic setting. Pressure-release melting from upward mantle flow, however, is increasingly cited as a secondary driver of mantle wedge melting. Here we report new SIMS volatile and LA-ICP-MS trace element

ODP Preliminary Report, 1996

The Cretaceous/Tertiary (K/T) and ocean history goals of ODP Leg 165 were accomplished through dr... more The Cretaceous/Tertiary (K/T) and ocean history goals of ODP Leg 165 were accomplished through drilling at five sites. Highlights of the leg included the recovery of K/T boundary clays and ejecta deposits (at Site 1001 and perhaps Site 999), and the recovery of igneous basement from the Caribbean Oceanic Plateau (Site 1001). Beyond any of our pre-cruise goals or expectations, we discovered a spectacular record of Eocene and Miocene explosive volcanism at Sites 998, 999, 1000, and 1001, which is unmatched in its magnitude and chronostratigraphic resolution. This includes the first documentation of arc volcanism along the Cayman Ridge. Also recorded above the excellently preserved basement/sediment contact in the two holes at Site 1001 is a mid-Campanian volcanic episode, probably the waning stages in the formation of the basaltic plateau that is the foundation of the Caribbean Plate. The age, physical characteristics, and geochemistry of the underlying basalts will bear importantly on the tectonic history of the Caribbean. The vesicularity of the basalts, the benthic microfossils found in sediments resting on the flows, and the magnetic directions recorded by the flows indicate the plateau was rapidly subsiding and near the paleoequator in the mid-Campanian. Geochemical results indicate that dispersed volcanic ash (excluding discrete ash layers) is a significant constituent (typically 10% to 20%) of the Caribbean sedimentary record. The ash alteration products strongly influence the composition of pore waters and may be an important source of silica for the vast accumulation of cherts that abound in the Eocene marine record. Important paleoceanographic events recovered by drilling include the K/T boundary, the "late Paleocene thermal maximum" (LPTM), and a middle/late minimum in carbonate accumulation ("carbonate crash"). All three holes from which the K/T boundary interval was recovered contained an unusual limestone layer that directly overlies clays and claystone. The limestone, though only a few centimeters thick, is anomalous in that it appears more massive, more indurated, and lighter in color (white to very light gray) than any other limestone recovered during the leg. The LPTM also marks a change in lithology and physical properties, characterized by a faintly laminated claystone unit, less than one meter thick, with significantly lower carbonate content than surrounding chalks and limestones. The spatial distribution of a middle/late Miocene minimum in carbonate accumulation ("carbonate crash") was extended from a regional anomaly in the Pacific to an interbasinal tropical anomaly. In addition to these anomalies, the transect of sites with Leg 165 Preliminary Report Page 8 depths ranging from 916 mbsf (Pedro Channel, Site 1000) to 3260 mbsf (Hess Escarpment, Site 1001) and with continuous depositional sequences offers the opportunity to study Neogene water mass history and circulation across the basin. Finally, Site 1002 from the anoxic Cariaco Basin contains a unique tropical counterpart to high latitude ice cores for studies of large and abrupt climate changes in the latest Quaternary.