About 56 million years ago, a massive release of carbon warmed Earth by more than 5 °C. This event, the Paleocene–Eocene Thermal Maximum (PETM), is one of the best geologic analogs for modern climate change, so how rivers responded to it can tell us how rivers might respond to future warming.
I study PETM river deposits in the Bighorn Basin of northwestern Wyoming with Brady Foreman (Western Washington University) and Akshay Mehra (University of Washington). We combine field sedimentology with drone photogrammetry, building three-dimensional point clouds of outcrops to measure sedimentary structures remotely, and we use paleocurrents to reconstruct the planform of ancient rivers.
So far, the rivers do not appear to have gotten bigger during the PETM: we see no clear change in flow depth, channel planform, or the flow conditions recorded by bedforms. Instead, they reworked their floodplains faster and left behind a much wider channel belt. This matters because about two billion people live on floodplains, and a river that shifts across its floodplain more quickly can erode the farms, homes, roads, and bridges along its banks, even if the river itself gets no bigger. That pace also sets how long sediment and carbon are stored on floodplains, with major implications for the carbon cycle.
We currently have two papers in review, so check back soon to take a look at those!
