DIFFERENTIATING PATH AND SOURCE PROCESSES IN COMPLEX GEOLOGIC STRUCTURE THROUGH PASSIVE SEISMIC STUDIES: BERING GLACIER, ALASKA AND VILLARRICA VOLCANO, CHILE

Measuring shallow seismic sources provides a way to reveal processes that cannot be directly observed, but the correct interpretation and value of these signals depend on the ability to distinguish source from propagation effects. Furthermore, seismic signals produced by a resonating source can look almost identical to those produced by impulsive sources, but modified along the path. Distinguishing these two phenomena can be accomplished by examining the wavefield with small aperture arrays or by recording seismicity near to the source when possible. We examine source and path effects in two different environments: Bering Glacier, Alaska and Villarrica Volcano, Chile. Using three 3-element seismic arrays near the terminus of the Bering Glacier, we have identified and located both terminus calving and iceberg breakup events. We show that automated array analysis provided a robust way to locate icequake events using P waves. This analysis also showed that arrivals within the long-period codas were incoherent within the small aperture arrays, demonstrating that these codas previously attributed to crack resonance were in fact a result of a complicated path rather than a source effect. At Villarrica Volcano, seismometers deployed from near the vent to ~10 km revealed that a several cycle long-period source signal recorded at the vent appeared elongated in the far-field. We used data collected from the stations nearest to the vent to invert for the repetitive seismic source, and found it corresponded to a shallow force within the lava lake oriented N75°E and dipping 7° from horizontal. We also used this repetitive signal to search the data for additional seismic and infrasonic properties which included calculating seismic-acoustic delay times, volcano acoustic-seismic ratios and energies, event frequency, and real-time seismic amplitude measurements. These calculations revealed lava lake level and activity fluctuations consistent with lava lake level changes inferred from the persistent infrasonic tremor.

Alpine Plants and Climate Change in Glacier National Park, New Zealand and Scotland

The first part of the lecture details a study of how receding glaciers and snowfields in Montana, New Zealand and Scotland affect the alpine plants that grow along and near their edges. Measuring and monitoring techniques are included. The second part describes the Global Observation Research Initiative in Alpine Environments (GLOBAL) whose purpose is "to establish and maintain a world-wide long-term observation network in alpine environments. Vegetation and temperature data collected at the GLORIA sites will be used for discerning trends in species diversity and temperature."

Tracing glacier wastage in the Northern Tien Shan (Kyrgyzstan/Central Asia) over the last 40 years

The status and dynamics of glaciers are crucial for agriculture in semiarid parts of Central Asia, since river flow is characterized by major runoff in spring and summer, supplied by glacier- and snowmelt. Ideally, this coincides with the critical period of water demand for irrigation. The present study shows a clear trend in glacier retreat between 1963 and 2000 in the Sokoluk watershed, a catchment of the Northern Tien Shan mountain range in Kyrgyzstan. The overall area loss of 28% observed for the period 1963–2000, and a clear acceleration of wastage since the 1980s, correlate with the results of previous studies in other regions of the Tien Shan as well as the Alps. In particular, glaciers smaller than 0.5 km2 have exhibited this phenomenon most starkly. While they registered a medium decrease of only 9.1% for 1963–1986, they lost 41.5% of their surface area between 1986 and 2000. Furthermore, a general increase in the minimum glacier elevation of 78 m has been observed over the last three decades. This corresponds to about one-third of the entire retreat of the minimum glacier elevation in the Northern Tien Shan since the Little Ice Age maximum.