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EARTH SCIENCE
A data-set compilation suggests that measurements of river erosion into rock depend on the observation timescale, casting doubt on whether terraces and other incised landforms faithfully record changes in climate and tectonics. SEE LETTER P.391
The pattern and ages of relict landforms, such as terraces, that are incised by rivers provide the best record of changes in Earth's surface elevation over millennial to million-year timescales. As a result, much work has been devoted to deter- mining the age of bedrock landforms1 and sediment deposited on terraces2 and in caves3, to constrain the magni- tude and timing of river incision. On page 391 of this issue, Finnegan et al.4 challenge the perception that the ages of relict landforms along incised bed- rock rivers (Fig. 1) retain a signature of climatic and tectonic forcing. Instead, the authors argue that the intermittent nature of bedrock river incision means that attempts to measure long-term incision rates are inherently biased by the timescale over which they are averaged.
Bedrock rivers set the pace of land- scape evolution and form an important connection between Earth's tectonic and climatic systems. As mountain ranges are uplifted, increases in topo- graphic relief cause rivers to incise bedrock towards a balance between erosion and uplift. Furthermore, the ability of rivers to incise rock and transport sediment is controlled by the size and frequency of floods. Such floods are sensitive to changes in cli- mate that may in turn be driven by tectonic processes. In recent decades, provocative hypotheses5 regarding the potential coupling of climate, tectonics and erosion have impelled the need for a quantita- tive understanding of the mechanics of river incision6.
The idea of a link between the rates of change in surface elevation and the measure- ment timescale is well known in stratigraphy; this...