Landslides are not only a natural hazard, they also erode entire mountain ranges. The mobilization of rock and soils has far reaching implications for the concentration of CO2 in the atmosphere and it influences Earth’s climate. This February, we spent four weeks in the Southern Alps of New Zealand to investigate how landslides influence the global carbon cycle. We, that is Dr. Erica Erlanger – freshly graduated from the ETH Zurich and now a postdoc at the GFZ – and Alexander Gessner, Master student at the FU Berlin.
The Southern Alps of New Zealand are one of the fastest evolving mountain ranges on the planet. Uplift rates here are several millimeters per year, producing steep hillslopes that are rapidly eroded. Close to 100% of this erosion occurs by landsliding, and the fresh, fine rock mass in landslide deposits creates efficient reactors for chemical weathering. Chemical weathering is the dissolution of minerals by acidic groundwater. Much of the acid in the groundwater stems from dissolving atmospheric CO2 in water. Where this acid dissolves silicate rocks, calcium, magnesium, and bicarbonate (HCO3-) ions are produced that are washed into the ocean by rivers. In the ocean, these ions provide the ingredients for the formation of carbonate rocks (e.g. CaCO3) which effectively locks up the atmospheric CO2 into the rock record. By sampling springs from landslide deposits, we aim to build a model for how landslides influence chemical weathering in mountain regions. This project is part of the EU-funded Marie Skłodowska-Curie project WetSlide.
Landslides have another important impact on the carbon cycle, because they strip soil and vegetation from hillslopes. The soil and vegetation contain organic carbon and all carbon that makes it to the ocean can get locked up in rocks on the ocean floor. On the bare hillslopes, new soils can build up and lock up carbon from the atmosphere. On this trip, we sampled soils and measured how they grow over time by studying landslides that occurred anywhere from 1- to 1000 years ago.
