INSTAAR Geophysics Group

Geophysics Group

The general objective of the Geophysics Group is the application of modern mathematical, physical, and chemical knowledge to increase understanding of earth-system processes. The group seeks to understand how:

processes act to create the environment we live in today
past environments were produced
predicted climatic forcing will affect future environments
deep-earth processes have been involved in the development of the modern earth environment.

The Geophysics Group applies skills in solid and fluid mechanics & dynamics, heat transfer, chemistry, applied mathematics, solid-earth geophysical methods, and remote sensing. Members utilize theoretical analysis, numerical modeling, and quantitative field & laboratory study to investigate snow, ice, water, and sediments in the world's oceans, glaciers, and land areas.

Background

Public concerns ranging from sea-level rise, to deforestation, to degradation of ecosystems indicate that global change has become a pressing and controversial topic throughout the world. Disagreement persists about how the global environment may change in the future, and whether human activities are involved in climate change. Work in the INSTAAR Geophysics Group is broadly focused on understanding physical processes and objects (ocean, rivers, sediment, permafrost, glaciers, and snow cover) underlying the changing Earth system. Our research seeks this understanding on a global scale and for site-specific processes which have large-scale or global applications.

Recent Achievements

Global riverine sediment discharge: A new modeling system has been developed to provide global predictions on the terrestrial flux of sediment, on a river-by-river basis, under Modern and pre-Anthropocene conditions. Pre-Anthropocene sediment flux was likely 15.5 BT/yr. Human activities have increased fluvial sediment erosion by 2.3 BT/yr. Modern delivery of sediment is presently 12.6 BT/yr, due to an estimated trapping of 100 BT of sediment behind reservoirs. Seasonal patterns of sediment delivery are conditioned by precipitation patterns, snow-release periods, and human-influenced water release from reservoirs.

Hydrology, Sedimentation, and the Carbon Cycle: Terrestrial sedimentation may account for much of the so-called "missing carbon" in the earth's modern carbon cycle. The role of event-type processes, such as landslides and fire-flood events, as well as human activity are significant at hillslope to watershed scales.

Glacier Changes and Sea-Level Rise: Regional to global syntheses of glacier mass balance continue to address problems of detecting current and predicting future sea-level change. Most glaciers in the world are currently retreating and becoming thinner, accounting for approximately 20% of global sea-level rise during the last century. The most recent analysis of global mountain and subpolar glaciers reveals that their regime shifted to a new mode in 1988, with increased air temperature sensitivity and increased annual rate of contribution to sea-level rise. The annual rate of glacier contribution to sea-level rise generally has been increasing: 0.15 mm yr-1 from1961-76, 0.24 mm yr-1 from 1977-87, and 0.41 mm yr-1 from 1988-98. Our publically available mass balance datasets have been used by collegues for a number of studies including the influence of glacier changes on Earth’s inertia and rotation rate.

Coastal Sediment Dynamics and Structure:Oceanic margins contain a wealth of information relevant to mineral resources, geologic history, and oceanographic and climate change. New models developed at INSTAAR incorporate processes of sediment dispersal and stratigraphic evolution, with application to modern environmental assessment, global warming scenarios, natural disaster mitigation, oil exploration, and national security.

Antarctic Subice Structure: Antarctic Subice Structure: Aeromagnetic surveys combined with radar sounding reveal dynamics of the West Antarctic Ice Sheet and the evolution of underlying bedrock. High amplitude magnetic anomalies at the base of the ice are due to volcanic sources over large areas. Subglacial eruptions were common but their edifices are poorly preserved due to glacial erosion. Volcanically induced subglacial uplift of the Sinuous Ridge at the ice divide may have forced a large advance of the West Antarctic Ice Sheet.

Iceberg Calving: The terminus of the Columbia Glacier, the largest tidewater glacier draining the Chugach Mountains of south-central Alaska, has retreated at a rate of about 1 km/yr. High calving rates have been partially offset by steadily increasing ice velocity. As ice continues to thin, and the terminus retreats into a 500-meter-deep basin, rapid and dramatic changes in the state of the Columbia Glacier are inevitable.

Glaciated Continental Margins: Arctic margins are some of the least explored submarine environments on the surface of the earth. They formed under the influence of ice sheets that once advanced to the edge of the continental shelves, and when sediment was dispersed directly into the deep ocean. Continental slopes along the margins of Greenland and Iceland, for example, are very different, having experienced different ice sheet conditions. The Greenland continental slopes developed under the influence of polar ice conditions when basal till was intermittently remobilized as debris flows. The Icelandic continental slopes developed under the influence of more temperate ice conditions and sediment dispersal was more by turbidity currents and surface plumes.

Predicting the sediment flux from land to the ocean: Refined hydrological models are linked to global data sets through web distributed (DODS) systems and offer the ability to 1) globally predict the monthly water and sediment load of rivers with drainage basins larger than 25,000 km2, 2) individually predict the daily discharge and sediment load of any river with a drainage basin larger than 1,000 km2, 3) predict the type discharges (water and sediment) for selected rivers during periods of ice age conditions using simulated paleoclimate scenarios (i.e. CCM2).

Jökulhlaups (Glacial outburst floods): Sudden release of water impounded by a glacier can produce much larger floods than weather-induced floods. At Kennicott Glacier, Alaska, an annual jökulhlaup from Hidden Creek Lake provided the opportunity to plan observations of one of these events through its entirety. Results from 1999 and 2000 show that there was no leakage prior to the outburst, about 20% of the lake water was stored under the ice adjacent to the ice dam, the hydrograph passed through the glacier essentially unchanged, and the flood strongly perturbed the subglacial hydrology as seen in the hydrochemistry and changes in water levels in basins along the glacier. The conditions that trigger ice-dammed lake drainage remain under study.

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