Volcanic Landscapes: How Water Shapes Them Over Time

Volcanic areas are some of the most active places on Earth, but we don't understand them very well. Let's look at the central Cascade arc in the USA. Here, water and landforms change together in a systematic way, linked to how old the volcanic rocks are. At the Cascade crest, where there's a lot of recent volcanic activity, water flows deep through the top 1 km of the Earth's crust. But as you move away from this hotspot, the water flow becomes shallower and more horizontal. This pattern shows how water's behavior changes over time in what scientists call the "deep Critical Zone. " Three main factors drive this change: chemical weathering deep underground, the deposition of particles on the surface, and tectonic forces. These factors push the landscape from a state with little topographic dissection, high vertical water flow, many lakes, and steady water levels, to one with deep river cuts, low vertical water flow, few lakes, and sudden water level changes.This shift is important for water resources in the region. Temperature readings from drill holes suggest there's at least 2 km of actively flowing groundwater at the Cascade Range crest, with water discharge varying a lot depending on the age of the rocks. Deeply circulating water also affects volcanism. Explosive magma-water interactions have been seen in Holocene eruptions in the High Cascades, increasing the potential for volcanic hazards. So, the state shift in the Critical Zone drives the evolution of volcanic landscapes in wet climates. It's a key to understanding how the Earth's solid parts and climate are connected in these regions.