CG11A-01
Modelling Glacier Surface Temperature Using Weather Station Data and Historical Climate Reconstructions
Models of glacier response to climate change and snow/ice melt require knowledge of air temperatures at the glacier surface. This can be directly measured at selected locations, but distributed models of glacier melt require temperature information over an entire surface. Furthermore, in many practical applications, temperature must be estimated for locations where no data is available. A new and more accurate model to extrapolate temperature has been developed at the Haig Glacier in Alberta to meet this need. Air temperature measurements collected at an array of sites since 2001, including an expanded station network in the summer of 2008 to examine the effects of proximity to a south-facing valley wall, are used to create the model. Air temperatures 1.5 m above the surface of the Haig Glacier are then computed using the new model from data collected at a weather station located at the foot of the glacier. Temperature and precipitation data collected from this station is supplemented with digital elevation models and synoptic reanalysis data from the National Center for Environmental Prediction. The new temperature model accounts for differences in the effect of elevation, incoming solar radiation, albedo, regional weather systems, and valley walls on temperature between the weather station and a point on the glacier surface. This model yields hourly air temperature values across the glacier to a 25 m horizontal resolution. The new method of temperature extrapolation shows a considerable improvement over the constant lapse rate model in terms of accuracy and increased spatial variability. This model can be applied to simulations of summer melt and runoff from the Haig Glacier and from neighbouring ice masses, providing a tool for estimating catchment-scale melt water discharge and the sensitivity of glacier runoff to climate warming.
CG11A-02
Electromagnetic Land Surface Classification by Integrated Multi-Spectral and Polarized Radar Remote Sensing Data
We present a new hierarchical electromagnetic (EM) land surface classification scheme by the integration of high-resolution multi-spectral optical and polarimetric SAR images. In addition to spectral characteristics of the reflected surface conventionally extracted from multispectral images, backscattered amplitude of radar image is used to classify land surface in terms of EM parameters such as permittivity, conductivity, permeability, surface roughness, correlation length, and specific attenuation parameters. A hybrid classification algorithm is developed, in which direct field and lab EM measurements data as well as data from literatures are used. The new classification scheme gives us new insight on the wave propagation modeling for a mobile communication and electrical hazard estimation.
CG11A-03
Drought Impact Characterization for the Canadian Prairie Using Remote Sensing and Ecosystem Models
Drought can cause diverse impacts on terrestrial ecosystems and land surface including plant physiology, surface albedo, hydrology, carbon sequestration, etc. Accurate characterization of drought impact is not only required for drought and drought-related studies, it is also an important component in assessing the social- economical impact and in decision making. In this presentation we will discuss the spatial-temporal distributions of the impact of the drought occurred around 2001-2003 over the Canadian prairies. Our method is based on the integration of satellite observations and the ecosystem model EALCO. Parameters used to illustrate the drought impacts include canopy stomatal conductance, vegetation indices (e.g., NDVI), land surface albedo, fraction of absorbed photosynthetically active radiation (fAPAR), evapotranspiration, and plant productivities.
CG11A-04
Volcano Instability Induced by Resurgence at the Ischia Island Caldera (Italy), and the Tsunamigenic Potential of the Related Debris Avalanche Deposits: a Complex Source of Hazard at Land-sea Interface
Slope instability is a common feature in the evolution of active volcanic areas. The occurrence of mass movements is doubly linked to volcanism and volcano-tectonism, which act as either preparing factor (through increased topographic gradients or emplacement of unconsolidated deposits on slopes) or triggering factor (through earthquakes and/or eruptions). Debris avalanches and lahars in active volcanic areas are an additional factor of hazard, due to their high destructive power. Moreover, volcanoes located in coastal areas or on islands, may experience lateral collapses with the potential to generate large tsunamis. Ischia is an active volcanic island in the Gulf of Naples. Volcanism begun prior to 150 ka and continued, with periods of quiescence, until the last eruption in 1302 A.D. It has been dominated by a caldera-forming eruption (55 ka), which was followed by resurgence of the caldera floor. Volcanism and gravitational mass movements have been coeval to resurgence, which generated a maximum net uplift of about 900 m over the past 33 ka. Resurgence occurred through intermittent uplifting and tectonic quietness phases. During uplift, volcanism and generation of mass movements were very active. The resurgent area is composed of differentially displaced blocks and has a poligonal shape, resulting from reactivation of regional faults and activation of faults directly related to volcano-tectonism. The western sector is bordered by inward-dipping, high-angle reverse faults, cut by late outward-dipping normal faults due to gravitational readjustment of the slopes. The north-eastern and the south-western sides are bordered by vertical faults with right transtensive and left transpressive movements, respectively. The area located to the east of the most uplifted block is displaced by outward- dipping normal faults. Some giant landslides and their relationships with volcano-tectonism have been recognized at Ischia. Their deposits are intercalated with primary volcanics and minor landslide deposits in the eastern sector of the island. Within the northern and western sectors, historical earthquake-triggered landslides are well exposed, also due to lack of recent volcanic rocks. The largest landslide bodies seem to have a submarine counterpart, as evidenced by the hummocky topography of the seafloor in the offshore of the island. The recognized landslides vary from small lahars to large debris-avalanche, whose detachment areas are clearly conditioned by the geometry of the same structures that drove resurgence and fed volcanism. Tsunami hazard in the Gulf of Naples has not yet evaluated, even though potential for tsunami generation exists due to the recognized cases of slope failure. The catastrophic collapse that formed the big scar in the southern flank of Ischia can be taken as the upper limit case for tsunamigenic failures on the island, although smaller episodes have also to be taken into account. Ischia subaerial slopes are known to be prone to failures: although usually subaerial landslides do not reach the sea, the case of a tsunamigenic subaerial failure cannot be ruled out. Further the existence of a lot of scars along the submarine flanks of the edifice, evidences several past events and scenarios of possible future landslides.
CG11A-05
Geologic Subsidence in the Sacramento-San Joaquin Delta, California, and its Implications for Risk Assessment
California probably moves more water within its boundaries than any other political entity in the world. A key component of the state's water distribution system is the Sacramento-San Joaquin Delta. The decrease in land-surface elevation of artificial islands and tracts within the Delta is generally attributed to the draining of peat-rich wetlands and the subsequent disappearance of organic material through oxidation, wind erosion and other processes. This anthropogenic subsidence is of great concern because it increases pore pressure on the levees that surround the islands and tracts. Failure of Delta levees will have serious economic and social consequences not only locally, but for the entire state of California. However, the anthropogenic subsidence is superimposed on natural geologic subsidence that, for the most part, has received little attention in risk assessments. Ages for basal peat deposits in cores at 18 sites within the Delta indicate that peat formation began about 6500 years BP. At most sites the basal peat is about 9 meters below current sea level. Global sea level curves suggest that about 6500 years ago, sea level was only 3 meters below current sea level. Because peat is generally assumed to form at or slightly below sea level, the most reasonable interpretation of the data from the basal peat deposits is that about 6 meters of natural geologic subsidence has occurred in the Delta over the past 6500 years. A subsidence rate of about 1 meter per 1000 years agrees well with estimates deduced by Shlemon and Begg (1971) from the present depth of tilted, older alluvial fans in the Sacramento Valley. These observations have profound implications for the assessment and mitigation of risk in the Sacramento-San Joaquin Delta. First, the rate of geologic subsidence is comparable to the recent rate of sea level rise due to anthropogenic global climate change, and because these two effects operate in concert, stress increase on Delta levees may well be twice as rapid as has generally been assumed. Second, the on-going geologic subsidence coupled with evidence for relative tectonic stability to the west of the Delta suggests that a generally north-south, active fault trends through the middle of the region. And finally, global glacial-interglacial cycles, imposed on the long-term geologic subsidence, likely led to the formation and burial of thick layers of older peat that could significantly affect the seismic response of the region.
CG11A-06
Seabed Doming: a Precursor to Pockmark Formation?
Since their discovery in 1960's, the frequent occurrence of pockmarks on the ocean floor and their potential as a geohazard has led researchers to seek out and understand their presence. Evidence of seabed doming in pockmarked areas, combined with upward bending of sediment layers beneath many pockmarks and mud volcanoes suggests that doming may be a possible precursor to sediment failure and pockmark formation. The ability of fluids to migrate vertically due to buoyancy is well documented, but more recent studies have shown migration pathways to become horizontal under some conditions. Sediment layering can create planes of weakness along which fluid can migrate horizontally and result in local surface layer doming. Initial experiments using thin layers of gelatin and mixtures of mud-silt-sand particles show that horizontally migrating fluid under a thin layer of sediment causes uplift and doming of the surface in the shape of a spherical cap. Continued fluid flow between layers causes tensional failure of the surface layer and release of the fluid from a focal point, resulting in a pockmark-like feature. The induced doming can be described using thin-plate bending theory for domes whose diameters are many times greater than the overlying layer thickness. From the theory, stress created in a domed seabed can be nearly two orders of magnitude larger than the pressure applied by the underlying fluid. This can allow for low relief domes to induce large tensile stresses while going undetected by most acoustical imaging methods.
CG11A-07
Landslide-Generated Tsunami Hazards in Fiordland, New Zealand and Norway
Sub-aerial or submarine landslides can generate large displacement waves, sometimes with devastating consequences. Catastrophic rockslides fall into the fiords of western Norway about every 100 years: during the last century, 174 people have been killed by landslide-generated tsunami, including the 1934 Tafjord rockslide which generated a 62 m high wave, killing 41 people. Hazard evaluation for the Norwegian fiords is based on high-resolution sonar imagery of landslide deposits, seismic reflection data, and event chronology developed from radiocarbon and surface exposure dating. The ongoing hazard is managed by identifying and monitoring potential failure areas, calculating slide paths and estimating slide properties at the points of impact. High-risk locations are monitored intensively, and include the Aknes slide area on Geirangerjord which could generate a tsunami of up to 30 m in height, and the Akernes landslide above Storfjorden. The current system of hazard evaluation and mitigation in western Norway is effective because large landslides are normally preceded by smaller rockfalls and by accelerating motion of the rock bodies. By contrast, large landslides in the very similar but highly seismic terrain of Fiordland, southwestern New Zealand are most likely earthquake-initiated, and therefore precursory minor rockfalls are unlikely. Coseismic landslides are common in New Zealand; seismic shaking serves as the primary trigger for failures that are preconditioned by progressive degradation of rock mass strength since deglaciation. The seismicity of Fiordland is dominated by the plate-boundary Alpine Fault, which runs immediately offshore of the popular tourist destination of Milford Sound; it has ruptured at least four times in the past 1000 years (the last time around 1717 A.D.) producing earthquakes of about magnitude 8. The probability of an earthquake of similar magnitude occurring along the Alpine Fault within the next 50 years is estimated at 65% plus/minus 15%. New seismic reflection and high-resolution sonar data from the fiords of New Zealand clearly show the presence of large rock avalanche deposits. I compare the distribution of landslide deposits in Milford Sound to that in Tafjord in Norway, and compare the means available to manage the hazard risk in both locations.