USGS Science⌕ Search

Geology topics

T. J. Wilson

Publications and source records attributed to T. J. Wilson.

5 recordsLinked to original sources
USGS2019

Impacts of the 2015 eruption of Calbuco volcano on Chilean infrastructure, utilities, agriculture, and health

This report presents data and summarises the findings of a reconnaissance trip investigating the impacts of the April 2015 eruption of Calbuco volcano, Chile, undertaken in November-December 2016. This study is mostly focused on the Los Lagos region, focusing on impacts occurring within ~30 km of the volcano, which includes the tourism town of Puerto Varas and port city of Puerto Montt. Eruption impacts and response strategies may be similar for moderate size eruptions from other stratovolcanoes in temperate regions. As such, this study provides useful information for development of contingency plans at active volcanoes around the world. The 2015 eruption of Calbuco volcano began at 18:04 (local time) on 22 April 2015 and consisted of three eruptive phases. The first lasted for 1.5 hours and generated a 15-km eruption column and plume that was directed towards the northeast. Pyroclastic density currents (PDCs) were generated locally and distributed radially, affecting many of the major rivers. A second phase began at 01:00 (local time) on 23 April 2015, lasted six hours and generated a 17-km high eruption column and plume that was dispersed towards the north-northeast, and the most voluminous pyroclastic density currents of the sequence. A third eruptive phase occurred on 30 April 12:10 (local time) resulting in a 5-km column and plume dispersed towards the east.

Calbuco volcano↗
USGS2007

Elongate summit calderas as Neogene paleostress indicators in Antarctica

The orientations and ages of elongate summit calderas on major polygenetic volcanoes were compiled to document Miocene to Pleistocene Sh (minimum horizontal stress) directions on the western and northern flanks of the West Antarctic rift system. Miocene to Pleistocene summit calderas along the western Ross Sea show relatively consistent ENE long axis trends, which are at a high angle to the Transantarctic Mountain Front and parallel to the N77ºE Sh direction at Cape Roberts. The elongation directions of many Miocene to Pleistocene summit calderas in Marie Byrd Land parallel the alignment of polygenetic volcanoes in which they occur, except several Pleistocene calderas with consistent NNE to NE trends. The overall pattern of elongate calderas in Marie Byrd Land is probably due to a combination of structurally controlled orientations and regional stress fields in which Sh is oriented NNE to NE at a moderate to high angle to the trace of the West Antarctic rift system.

Open-File Report↗
USGS2007

Seismic facies and stratigraphy of the Cenozoic succession in McMurdo Sound, Antarctica: Implications for tectonic, climatic and glacial history

A new stratigraphic model is presented for the evolution of the Cenozoic Victoria Land Basin of the West Antarctic Rift, based on integration of seismic reflection and drilling data. The Early Rift phase (?latest Eocene to Early Oligocene) comprises wedges of strata confined by early extensional faults, and which contain seismic facies consistent with drainage via coarse-grained fans and deltas into discrete, actively subsiding grabens and half-grabens. The Main Rift phase (Early Oligocene to Early Miocene) comprises a lens of strata that thickens symmetrically from the basin margins into a central depocenter, and in which stratal events pass continuously over the top of the Early Rift extensional topography. Internal seismic facies and lithofacies indicate a more organized, cyclical shallow marine succession, influenced increasingly upward by cycles of glacial advance and retreat into the basin. The Passive Thermal Subsidence phase (Early Miocene to ?) comprises an evenly distributed sheet of strata that does not thicken appreciably into the depocentre, with more evidence for clinoform sets and large channels. These patterns are interpreted to record accumulation under similar environmental conditions but in a regime of slower subsidence. The Renewed Rifting phase (? to Recent, largely unsampled by coring thus far) has been further divided into 1, a lower interval, in which the section thickens passively towards a central depocentre, and 2. an upper interval, in which more dramatic thickening patterns are complicated by magmatic activity. The youngest part of the stratigraphy was accumulated under the influence of flexural loading imposed by the construction of large volcanic edifices, and involved minimal sediment supply from the western basin margin, suggesting a change in environmental (glacial) conditions at possibly c. 2 Ma.

Open-File Report↗
USGS2002

Draped aeromagnetic survey in Transantarctic Mountains over the area of the Butcher Ridge igneous complex showing extent of underlying mafic intrusion

A draped aeromagnetic survey over the area surrounding the Butcher Ridge igneous complex (BRIC), Transantarctic Mountains, was acquired in 1997–1998 as part of a larger Transantarctic Mountains Aerogeophysical Research Activity survey. The BRIC is a sill-like hypoabyssal intrusion ranging in composition from tholeiitic basalt to rhyolite. An 40 Ar/ 39 Ar age of 174 Ma and the chemical character of the basaltic rocks show the BRIC to be part of the widespread Jurassic Ferrar suite of continental tholeiitic rocks, that extends for 3500 km across Antarctica. The aeromagnetic survey shows a horseshoe-shaped pattern of anomalies reaching amplitudes as great as 1900 nT generally associated with the bedrock topography where it is exposed. It is apparent that the high-amplitude anomaly pattern is more extensive than the 10-km-long exposed outcrop, first crossed by a single 1990 aeromagnetic profile. The highest-amplitude anomalies appear south of the profile acquired in 1990 and extend out of the survey area. The new aeromagnetic data allow determination of the extent of the interpreted Butcher mafic(?) intrusion beneath exposures of Beacon sedimentary rock and ice in the area covered, as well as beneath the small BRIC exposure. The magnetic anomalies show a minimum area of 3000 km 2 , a much greater extent than previously inferred. Magnetic models indicate a minimum thickness of ∼1–2 km for a horizontal intrusion. However, nonunique models with magnetic layers decreasing in apparent susceptibility with depth are consistent with of a 4- to 8-km-thick layered intrusion. These magnetic models indicate progressively deeper erosion of the interpreted mafic-layered body from the south to north. The erosion has removed more magnetic upper layers that mask the magnetic effects of the lower less magnetic layers. The probable minimum volume of the intrusion in the area of the survey is ∼6000 km 3 . An alternate, but less likely, interpretation of a series of dikes can also fit the observed magnetic anomalies.

Journal of Geophysical Research B: Solid Earth↗