Fluvial Geomorphic and Hydrologic Evolution and Climate Change Resilience in Young Volcanic Landscapes: Rhyolite Plateau and Lamar Valley, Yellowstone National Park
Quaternary volcanism associated with the last caldera cycle in Yellowstone National Park included emplacement of ash-flow tuffs, massive rhyolite flows ranging from 79 to 484 ka, and valley-filling basalts. This study examines (1) the evolution of spring hydrology with flow age on the Rhyolite Plateau, (2) initial development and evolution of stream networks on the rhyolite flows, and (3) the impact of the 630 ka caldera formation and volcanic flow emplacement on Lamar Valley incision rates.
Integrated stream networks formed within 79 kyr on the Rhyolite Plateau. Incision is focused on steep flow margins and knickpoints and is dependent on local stream power. Plugging of fractures causes hydraulic conductivity of the flows to decline over time. Snowmelt infiltrates rapidly into younger flows, leaving ephemeral surface streams, but many flow-margin springs experience a delayed snowmelt response and enhanced discharge during late-summer periods of water stress, providing important refugia for aquatic organisms threatened by climate change.
Incision rates over the past 630 kyr in the Lamar Valley are greatest (≤ 0.55 mm/yr) where the greatest thickness of Quaternary volcanic material was emplaced, where they are higher than most rivers in the region. Incision rates are lowest (≤ 0.15 mm/yr) above a knickpoint caused by erosion resistant crystalline bedrock, and in the upper reaches of two tributaries, where I infer that faulting associated with caldera formation led to stream capture of portions of the headwater areas
