How Many Years Can a Mountain Exist before it's Washed to the Sea? Or, Bob Dylan's Theory of Landscape Evolution

Abstract

The question of the persistence of topography is not just a line in one of the most famous songs ever written, it is also one of the long-standing questions in geomorphology. Mountains created by tectonic processes hundreds of millions of years ago still stand proud in the landscape, posing intriguing questions of how topography can persist for such a long time, and if the mountains we see today are the result of more recent processes, and therefore not a direct relict of the original topography. Although models have been proposed to explain the antiquity of topography, the only way to test these models is by providing denudation rates over millions of year time scales. Such data can be uniquely provided by low temperature thermochronometers. In this paper we provide a brief review of these techniques and an example from western Scotland where the thermochronometers have been applied to determine the age of first order topography. The results indicate that although denudation rates have been temporally and spatially variable in the last ∼300 Ma, the macro-topography has not changed significantly.

Key Words:

• First-order topography
• persistence of topography
• millions of year time scale
• low temperature thermochronometers
• denudation rates
• Scotland