Topography, groundwater, river discharge, and weathering co-evolve across the Oregon Cascade Range

What is it about?

A study of the volcanic central Cascade Range in the United States finds that the manner in which water moves through and erodes the landscape likely undergoes a significant shift as the volcanic bedrock ages, and proposes that this “Critical Zone state shift” explains similar patterns seen in volcanic regions globally. The initial state of the terrain, located at the crest of the range where volcanism is currently active, is minimally shaped by rivers and dotted with lakes and hosts an active groundwater reservoir with volume similar to major continental lakes.

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Why is it important?

Understanding the near-surface environment where atmospheric and solid earth processes interact, often termed the `Critical Zone', is important for assessing resources and building resilient societies. This paper examines a volcanic landscape in the Oregon Cascade range, an understudied Critical Zone setting that is host to major regional water resources, high rates of silicate weathering, and significant geohazards (volcanic eruptions). We show that the volcanic Critical Zone undergoes a structural shift, from depth extents of >1 km to meters, over timescales of ~1 million years. We map an active groundwater volume of at least 81 cubic km, comparable to major continental lakes, stored at the Cascade range crest. This state shift makes volcanic landscape evolution a unique probe of deep coupling between Earth systems.