Research Projects

Geomorphic history and fluvial responses to active tectonics and climate change in an uplifted forearc region, Pacific coast of southern Costa Rica, Central America

PI: Tom Bullard and S.G. Wells

Project Period: 1986 - 1988

Funding: National Science Foundation

Keywords: Quaternary geology, Costa Rica, geomorphology, active tectonics, soil-geomorphology, earthquakes

Project Description

Identifying and characterizing fluvial terraces and fluvial geomorphology along Río Grande de Térraba (Río Térraba) provide the necessary data for assessing Quaternary fluvial adjustments to active tectonics in an uplifted forearc region of the convergent plate margin of southern Costa Rica. Uplift initiated in the Pliocene and continues in response to partial subduction of the aseismic Cocos Ridge (Cocos Plate) beneath the Caribbean Plate. Quaternary geologic mapping, soil geomorphology, tectonic geomorphology, and radiocarbon dating were used to elucidate spatial differences in the tectonic framework, uplift rates, and geomorphic responses. Although grain-size data for the Pleistocene and Holocene fluvial deposits suggest little change in the hydrology of Río Térraba in the past 35,000 yr, terrace remnants and sedimentology document changes in clast composition, sinuosity, gradient, and knickpoint migration. Evidence shows stream captures related to tectonic activity involving significant drainage reorganization in the lower Río Térraba, whereas late Pleistocene and Holocene climate change may be a factor in some smaller scale stream captures. The development of synchronous alluvial sequences throughout the uplifted forearc region argues for climate influence on geomorphic processes in addition to the strong tectonic signal contained in the geomorphic record.

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