December Geology and GSA Today ...( to available geological evidence. Eur...)

to available geological evidence. Europe and the Mediterranean ca. 3 Ma can be described as both seasonally and annually warmer and wetter than present. The cause for these changes relate to reduced land and sea ice cover in the Northern Hemisphere, which in turn affected regional atmospheric pressure systems and wind strengths. In particular, increasing wind strengths and surface wind stress over the North Atlantic Ocean facilitated greater oceanic heat transport by producing a more vigorous flow of heat transporting surface ocean currents such as the Gulf Stream. If future climate warming reduces Northern Hemisphere land and sea ice cover, Europe and the Mediterranean may experience a climatic scenario akin to what occurred 3 million years ago.

Estimation of fault propagation distance from fold shape: Implications for earthquake hazard assessment.
Richard W. Allmendinger and John H. Shaw

As an unexposed (blind) thrust fault propagates, folding of the layers of rock is accompanied by earthquakes. The shape of these folds may record how far the fault tip has propagated relative to the amount of displacement of the blocks on either side of the fault. This information can tell us where in the Earth a fault nucleated. By applying this approach to the Puente Hills thrust-Santa Fe springs anticline in the Los Angeles basin, the authors show that the fault nucleated in the same part of the Earth as the subsequent Whittier Narrows earthquake.

Dead deltas former productivity: Two trillion shells at the mouth of the Colorado River.
Michal Kowalewski et al.

Biological productivity of the Colorado River delta is about 5% of what it was before the mighty Colorado's water was diverted for human uses. Since the 1930's theres been a drastic reduction in the number of shellfish that inhabit the rivers estuary because dams, diversions, and irrigation projects have reduced the flow of nutrient-laden fresh water to the Colorado Delta in Mexico. The sh
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Contact: Ann Cairns
acairns@geosociety.org
303-447-2020 ext 156
Geological Society of America
27-Nov-2000

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