Tectonics, Climate, and Mountain Topography

There is ongoing debate as to what specific roles climate and tectonics play in the topographic growth of mountains. It was established that mountain elevation is primarily influenced by crustal strength, rock uplift and surface denudation (Whipple 1999,2010). However, feedback mechanisms such as a link to climate have proved more difficult to prove and are a subject of debate amongst researchers. There are two major arguments, one side believes that plate tectonics are the primary driver of topographic growth and the correlations between growing mountains and climate are a result of uplift. While the other side believes that climate is the primary driver and that changes in tectonics forces are the result of a change in climate. There are physical arguments and numerical experiments that suggest the forces actively deforming mountain ranges are influenced by climate (Molnar et. al 1990). However, finding definitive evidence that climate does have a significant impact on mountain building is difficult. Multiple scientists have found correlations between periods of intense precipitation or glaciation and rising mountain elevations. However, other findings further supported the idea that the changes in climate were the result of uplift, creating a back and forth between the two with no definitive answer yet.

In 1990 Molanar and England proposed the idea that most of the phenomena commonly associated with uplift, are instead brought on by climate change. The authors pointed out that many of the arguments made in support of tectonics as the primary driver, could also be used to indicate climate change as the major influence on topographic growth. It was believed that increased rates of erosion driven by climate, combined with crustal thickening resulted in an isostatic rebound creating higher peak elevations (Molanar et. al 1990). Later studies suggested that variations in erosion rates caused by precipitation affect the mountains width, crustal deformation rates, and uplift (Willet,1999). While other studies found that high rates of uplift create greater relief resulting in in higher rates of erosion (Balco et. al, 2013). This is important because it establishes that erosion rates can be affected by precipitation but, that it is not the main driver of increased erosion. In 2006 scientists concluded that the heights of mountains are directly influenced by a glacial erosional process known as “Glacial Buzzsaw”, in which the height of mountain ranges are limited by the snowline altitude and extent of glacial relief above the snow line (Mitchell et. al 2006). A connection was found that variations in mountain height correlate with climate-driven snowlines and that differences in elevation were primarily due to variations in climate and not tectonic processes (Eghold et. al 2009). In 2015 (Michalak et. al) further built upon these ideas, using data collected from the Eastern Cordillera, the authors found accelerated rates of cooling during the mid-late to Miocene. This is important because the majority of rocks uplifted to the surface in the Maranon fold-and-thrust belt occurred during that same period. Additionally, large exhumation of rocks can result in lower global temperatures. This led the authors to conclude that a change in climate created more erosive environments, which when uplifted (tectonics), exposes more surface area increasing erosion rates.

To summarize, there are many ways in which tectonics and climate influence mountain topography. Climate can affect mountain topography in the form of erosional processes such as precipitation which affects fluvial denudation (Willet, 1999), and glacial processes such as glacial Buzzsaw (Mitchell et. al 2006). Then, through the process of isostatic rebound (Molnar et. al 1990), in which high rates or erosion or incision into a mountain, and crustal thickening generate an isostatic response, that results in higher elevations. Tectonics also play an important role in the topographic growth of mountain topography. High relief slopes created by uplift can result in increased erosion (Balco et. al 2013), while crustal thickness is also believed to limit the maximum potential height of a mountain (Beaumont et. al 2004). In most of these cases the general idea is that increased rates of erosion driven by climate, result in the uplift and deformation of the rock.

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