2024 KEYNOTE SPEAKERS

"Lithology in the driver’s seat: making sense of widespread river reorganizations in tectonically dead regions (and why it matters for biodiversity)" 

For decades, the slow rates of erosion in tectonically inactive, non-mountainous landscapes have fueled the misconception that intraplate, low-relief settings have little geomorphic activity. However, as known for over a century, many intraplate landscapes contain evidence suggestive of ongoing, widespread drainage network rearrangement via river captures and drainage divide migration. Paradoxically, it is in the purported undynamic, slowly eroding landscapes in continent interiors that the highest freshwater biodiversity is observed.  How can tectonically dead landscapes be so geomorphically alive and incredibly biodiverse? In this talk, I explore how the slow erosional exhumation of hard rocks can be the primary driver of systematic drainage network reorganizations in the absence of tectonic activity. The exhumation of variable rock types systematically reroutes rivers and provides the missing motor of vicariant events needed to shuffle the aquatic biota and create highly biodiverse freshwater systems.

"Track & Trace: Using cosmogenic nuclides to track landslide activity and trace landslide-derived sediment"

Landslides are a major erosion mechanism in mountain landscapes, one of the most sensitive erosional processes to changes in climate and tectonics, and a critical geohazard. However, our estimates of landslide activity are at best based on observations on 100 -101 year timescales, and in most cases, on a snapshot of their activity or an incomplete record of preserved landslides. This limits our ability to quantify the role of landslides on landscape evolution, and to evaluate the impact of climate change or human influence on landslide frequency, magnitude and spatial distribution.

In this talk, I will present two novel ways in which we can use cosmogenic radionuclides to quantify landslide activity over 102 -103 year timescales. First, I will show in situ 10Be concentrations from 17 recent landslides on the Southern Alps and Fiordland (New Zealand), and how, in combination with photogrammetry surveys of the landslide scars, these data can be used to infer long-term landslide frequencies. By comparing these 10 Be-based, long-term landslide frequencies with decadal, aerial imagery-based landslide

inventories, we can examine potential spatial and temporal changes in landslide activity. For the Southern Alps, I will compare these estimates of landslide activity with the magnitude and spatial distribution of denudation rates that can be inferred from recently published catchment-averaged 10Be concentrations.

Second, I will show how in situ 14C/10Be ratios can be used to trace landslide-derived sediment, because due differences in the production mechanisms of these nuclides, 14C/ 10Be ratios increase with bedrock depth, and landslides excavate deeper in the bedrock than other erosional processes. I will present preliminary data on 14C/10Be ratios from 9 landslides and 19 catchments testing the sensitivity of this isotopic pair to fingerprint landslide-derived sediment, and whether these isotopic signatures of landsliding are transmitted effectively at the catchment-scale and detectable in its fluvial sediment export.