It has been postulated that a steady state between erosional and
tectonic processes may develop in continental collision. However, it is
not clear whether steady state conditions can be reached for all
components of the landscape. Here we show, using landscape evolution
models and field evidence, that a true geomorphic steady state may never
be reached in the Southern Alps of New Zealand. The strong asymmetries
in tectonic uplift and tectonic advection and the onset of glaciations
constantly interact to prevent the landscape from reaching a topographic
steady state. Evidence suggests that the first- order geomorphology on
the western side of the Southern Alps is controlled by orographic
precipitation combined with extreme rates of tectonic uplift, whereas
the development of deep glacial valleys on the eastern side is initiated
by differential uplift along large faults. We also develop a first-
order equation, governing the dynamics of the Main Divide, to show that
both tectonic advection and fluvial erosion efficiency control the
position and the height of the main drainage divide. Using a two-
dimensional landscape evolution model, we demonstrate that the
transition from glacial to fluvial conditions at the end of the last
glaciation led to substantial modifications of the landscape: While the
main trunk channels get slowly uplifted, ridges are leveled down,
causing the relief to decrease. Hillslopes appear to be affected by
fluvial processes which seem to be driven by incision of river
tributaries. This reduction of relief will probably never reach a steady
state since warmer interglacial periods are substantially shorter than
glacial periods.