est coast of South America, is one of the driest places on Earth. Many geologists consider the desert to have formed more than 10 Ma. It has been proposed that the desert was generated by the uplift of the Andean mountain range, which created a rain shadow along the west coast of South America. The authors work shows that this isn't true. There is good evidence for the presence of permanent lakes and rivers in the area occupied by the present day Atacama Desert until up to 3 Ma. Studies of deserts in Africa show that they also became more arid 3 Ma. This suggests that whatever caused the increase in aridity affected at least the Southern Hemisphere, and probably the world. Because the Southern Hemisphere appears to have become drier ca. 3 Ma, the authors think that the Atacama Desert developed because of global climate change, rather than because of the growth of the Andes.

Mid-Cretaceous tectonic evolution of the Tongareva triple junction in the southwestern Pacific basin.

Roger L. Larson et al., Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882, USA. Pages 67-70.

A geological structure called the "Tongareva triple junction" has been mapped for the first time across more than 3200 km (2000 miles) of southwestern Pacific Ocean seafloor using a high-resolution sonar system. Longer than the Appalachian Mountains, this structure would extend from the U.S.-Canadian border to Cuba if laid out along the eastern coast of the United States. The researchers located the structure at the intersection of two distinctly different trends of elongated abyssal hills that mark two of three former tectonic plate boundaries. They mapped this intersection by zigzagging the research vessel back and forth across it as the sonar system traced out the shapes of the elongated hills on the seafloor 5 km below. The triple junction trace contains the geological history of three tectonic plates that met in Cretaceous time ca.
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Contact: Ann Cairns
acairns@geosociety.org
303-357-1056
Geological Society of America
4-Jan-2002

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