Abstract. Absent glacial erosion, mountain range
height is limited by the rate of bedrock river incision and is thought to
asymptote to a steady-state elevation as erosion and rock uplift rates
converge. For glaciated mountains, there is evidence that range height is
limited by glacial erosion rates, which vary cyclically with glaciations. The
strongest evidence for glacial limitation is at midlatitudes, where
range-scale hypsometric maxima (modal elevations) lie within the bounds of
Late Pleistocene snow line variation. In the tropics, where mountain
glaciation is sparse, range elevation is generally considered to be fluvially
limited and glacial limitation is discounted. Here we present topographic
evidence to the contrary. By applying both old and new methods of hypsometric
analysis to high mountains in the tropics, we show that (a) the majority are
subject to glacial erosion linked to a perched base level set by the snow
line or equilibrium line altitude (ELA) and (b) many truncate through glacial
erosion towards the cold-phase ELA. Evaluation of the hypsometric analyses at
two field sites where glacial limitation is seemingly marginal reveals how
glaciofluvial processes act in tandem to accelerate erosion near the
cold-phase ELA during warm phases and to reduce their preservation potential.
We conclude that glacial erosion truncates high tropical mountains on a
cyclic basis: zones of glacial erosion expand during cold periods and
contract during warm periods as fluvially driven escarpments encroach and
destroy evidence of glacial action. The inherent disequilibrium of this
glaciofluvial limitation complicates the concept of time-averaged erosional
steady state, making it meaningful only on long timescales far exceeding the
interval between major glaciations.