Temperature-controlled erosion dominates in the Western Southern Alps of New Zealand

The interplay of tectonics, climate, and erosion controls mountain topography, modulates Earth’s climate, and regulates the fluxes of sediments and solutes across Earth’s surface. Understanding and quantifying the complex processes behind this interplay remains one of the key challenges in the Earth Sciences. At the scale of mountain ranges, glacial erosion, river incision, and landsliding are the only processes that have been observed to be capable of balancing rapid rock-uplift rates. These processes are thought to link tectonics and climate through the influence of mountain elevations on orographic precipitation or glaciation.

The western Southern Alps of New Zealand (WSA) are one of the fastest-eroding ranges on Earth, where erosion has long been thought to be dominated by landsliding and glacial scouring. However, previous erosion studies in the WSA have been restricted to very few catchments, to decadal timescales, or to below the tree line, which has prevented evaluating the variables and processes controlling erosion at the orogen-scale over longer timescales. Here, 20 new in-situ ¹⁰Be catchment-averaged denudation rates, which mostly range between ~0.6-9 mm/yr, allow us to examine the controls and spatial distribution of denudation. We find that the proportion of catchment area within the 1500-2000 m elevation window explains >70% of the variability in denudation rates, more than any other variable. In the WSA, this elevation range is where temperatures most commonly fluctuate between -3ºC to -8ºC in the presence of water (the frost-cracking window), and includes the zone of recent glacial retreat and permafrost degradation. Our data hence suggests that temperature-controlled peri- and paraglacial erosional processes can balance some of the fastest rock-uplift rates on Earth, of several mm/yr. Therefore, these processes, which are also elevation-dependent, can play an important, but previously overlooked role in linking tectonics and climate and limiting mountain elevations.