Quantifying landscape differences across the Tibetan plateau : implications for topographic relief evolution

Abstract

We quantify the bulk topographic characteristics of the Tibet-Qinghai plateau with

specific focus on three representative regions: northern, central, and southeastern Tibet.

Quantitative landscape information is extracted from Shuttle Radar Topography

Mission digital elevation models. We find that the morphology of the Tibetan plateau is

nonuniform with systematic regional differences. The northern and central parts of the

plateau are characterized by what we suggest to call ‘‘positive topography,’’ i.e., a

topography in which elevation is positively correlated with relief and mean slope. A major

change from the internally drained central part of Tibet to the externally drained part of

eastern Tibet is accompanied by a transition from low to high relief and from positive

to ‘‘negative topography,’’ i.e., a topography where there is an inverse or negative

correlation between elevation and relief and between elevation and mean slope. Relief in

eastern Tibet is largest along rivers as they cross an ancient, eroded plateau margin at high

angle to the major strike-slip faults, the Yalong-Yulong thrust belt, implying strong

structural control of regional topography. We propose that the evolution of river systems

and drainage efficiency, the ability of rivers to transport sediments out of the orogen,

coupled with tectonic uplift, is the simplest mechanism to explain systematic regional

differences in Tibetan landscapes. Basin filling due to inefficient drainage played a

major role in smoothing out the tectonically generated structural relief. This mode of

smoothing started concurrently with tectonic construction of the relief, as most clearly

illustrated today in the Qilian Shan-Qaidam region of the northeastern plateau. In

the interior of Tibet, further ‘‘passive’’ filling, due to internal drainage only, continued to

smooth the local relief millions of years after the cessation of major phases of surface

uplift due to crustal shortening.