| Glacial processes have shaped conspicuous landscapes at the Earth surface. In alpine
environments, glacial pre-conditioning of the topography exerts a strong control on the
geomorphological response following glacier retreat. However, whether the late Cenozoic
climate cooling and onset of glaciation have had a widespread impact on mountain erosion
remains debated. Sediment budgets, in various mountain ranges and at a global scale, show
an increase in sediment fluxes during the late Neogene, although their interpretation as proxy
for increased erosion is challenged. In-situ low-temperature thermochronometry (including
recent developments such as 4He/3He and OSL thermochronometry) records rock
exhumation within the upper crust to quantify long-term erosion and relief histories. Here I
will review some recent thermochronometric studies that investigate the mountain
erosional and topographic response to glaciation, going from mid- to high-latitude
regions.
In the European Alps, recent apatite 4He/3He data combined with thermal-kinematic
modelling suggest a significant increase in topographic relief over the last ∼1 Myr,
with 1-1.5 km of valley deepening by large and erosive glaciers. This episode is
synchronous with the Mid-Pleistocene climatic transition from symmetric 40-kyr to
strongly asymmetric 100-kyr glacial/interglacial cycles. Similar findings in other
mountain ranges, as well as recent compilations at a global scale, point toward a
globally averaged (but more pronounced at mid-latitudes) increase in erosion rates
since 1-2 Ma. This would support the assumption that enhanced climatic variability
during the Plio-Pleistocene, rather than cooling through the Late Cenozoic, has
controlled mountain erosion and topography. However, in the high-latitude settings of
the Patagonian Andes and southern Alaska, which have been glaciated since the
late Miocene, new thermochronometric results show that a substantial increase in
erosion had already occurred at ∼6-8 Ma, when alpine glaciers first appeared at these
sites but under a less-oscillating climate. Interestingly, thermochronometric data
also imply an increase in topographic relief since ∼1 Ma in these high-latitude
settings.
These findings suggest that the erosional response to glaciation may have propagated
equator-ward since the Late Miocene, quite simultaneously in both hemispheres. They also
highlight threshold mechanisms in the erosional response to climate change, ultimately
intensifying over the last 1-2 Myr when climate variability enhanced. Evaluating the
influence of Plio-Pleistocene climatic oscillations on mountain erosion and topographic
evolution now requires quantification of glacial erosion rates with higher temporal and spatial
resolution. |