Landslides in action

There are lots of good resources about landslides and other mass movements available on the web.  The best is the Landslides Blog by Prof Dave Petley, University of Durham.http://blogs.agu.org/landslideblog/

He updates it regularly and it contains some excellent examples and explanations of mass movements and their impacts from around the world.

There's also a good You Tube video of a recent dramatic cliff collapse in Cornwall which is well worth looking at http://youtu.be/ZVjr4mii3cE

Ecology and geomorphology - the search for a signature of life on Earth

As my lecture on  'Ecology and Geomorphology' demonstrated, there are many direct and indirect ways in which vegetation, animals and microorganisms influence geomorphology.  Beavers create dams which affect whole water courses, badgers burrow and cause huge amounts of sediment to be moved around hillslopes, whilst vegetation can protect many soil surfaces from wind and water-based erosion.  But does all this biogeomorphic effort actually add up to anything recognisable?  Is there a signature of life on Earth? These questions have received much attention from geomorphologists over recent years, as evidenced by this paper by Dietrich and Perron which is well worth looking at.  Read it and see what you think...

The search for a topographic signature of life.

Dietrich WE, Perron JT.  Nature 2006, 439: 411-418

Abstract

Landscapes are shaped by the uplift, deformation and breakdown of bedrock and the erosion, transport and deposition of sediment. Life is important in all of these processes. Over short timescales, the impact of life is quite apparent: rock weathering, soil formation and erosion, slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions, dilate soil, disrupt the ground surface and add strength with a weave of roots. Over geologic time, biotic effects are less obvious but equally important: biota affect climate, and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution. Apart from the obvious influence of humans, does the resulting landscape bear an unmistakable stamp of life? The influence of life on topography is a topic that has remained largely unexplored. Erosion laws that explicitly include biotic effects are needed to explore how intrinsically small-scale biotic processes can influence the form of entire landscapes, and to determine whether these processes create a distinctive topography.

Why does geomorphology matter?

Geomorphology shapes the world around us, and in turn we have a dramatic impact on much of the landscape through our influence on earth surface processes.  This is, in a nutshell, one of the major reasons geomorphology matters.  An interesting recent example of the key influence of geomorphology, in this case tectonic geomorphology, on humans comes from an article in the Journal of Human Evolution by Bailey et al.  In it, they illustrate how tectonic processes made a clear difference to the early hominids in South Africa.  A simple news item on the findings of the paper can be found at:
http://www.sciencedaily.com/releases/2011/03/110303065358.htm

Further details can be found by reading the paper as a whole,

Landscapes of human evolution: models and methods of tectonic geomorphology and the reconstruction of hominin landscapes

Geoffrey N. Bailey, Sally C. Reynolds,  Geoffrey C.P. King

Journal of Human Evolution 2011, 60: 257-280

Abstract

This paper examines the relationship between complex and tectonically active landscapes and patterns of human evolution. We show how active tectonics can produce dynamic landscapes with geomorphological and topographic features that may be critical to long-term patterns of hominin land use, but which are not typically addressed in landscape reconstructions based on existing geological and paleoenvironmental principles. We describe methods of representing topography at a range of scales using measures of roughness based on digital elevation data, and combine the resulting maps with satellite imagery and ground observations to reconstruct features of the wider landscape as they existed at the time of hominin occupation and activity. We apply these methods to sites in South Africa, where relatively stable topography facilitates reconstruction. We demonstrate the presence of previously unrecognized tectonic effects and their implications for the interpretation of hominin habitats and land use. In parts of the East African Rift, reconstruction is more difficult because of dramatic changes since the time of hominin occupation, while fossils are often found in places where activity has now almost ceased. However, we show that original, dynamic landscape features can be assessed by analogy with parts of the Rift that are currently active and indicate how this approach can complement other sources of information to add new insights and pose new questions for future investigation of hominin land use and habitats.

Tectonics and climate: the great geomorphic battle

The twin controls of climate and tectonics are the major forces shaping the geomorphological landscape around us.  Much recent geomorphic work has gone into clarifying which is the most important, and how they interact.  Many recent studies focus in particular on the relationship between tectonic uplift and climatically-powered denudation in shaping mountains.  There are several good papers you can look at to find more about this topic, but I recommend as a starting point this paper by Egholm et al:

Glacial effects limiting mountain height.

Egholm DL, Nielsen SB, Pedersen VK, Lesemann JE.

Abstract

The height of mountain ranges reflects the balance between tectonic rock uplift, crustal strength and surface denudation. Tectonic deformation and surface denudation are interdependent, however, and feedback mechanisms-in particular, the potential link to climate-are subjects of intense debate. Spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first-order controls on mountain range width, crustal deformation rates and rock uplift. Moreover, limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus, such as those in Tibet and the central Andes. There are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw. Here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate-controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles. With the aid of a numerical model, we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier-sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline. The model thereby self-consistently produces the hypsometric signature of the glacial buzzsaw, and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces.

Nature. 2009 460:884-7.

The San Andreas fault



Looking west from Joshua Tree, with the San Andreas fault running straight across in the middel distance

 One of the many advantages of being on sabbatical in Los Angeles is the opportunity to visit some prime geomorphological sites.  On a recent trip to the Joshua Tree National Park I had this great view over the San Andreas Fault from a local viewpoint.  As you can see the fault really does have a clear landscape presence.

Himalayan tectonics and landscape

There are lots of reports and papers about the Himalayas and the Tibetan Plateau, which I will refer to in susbequent posts, but perhaps a good starting point is the on-line chapter from the book 'Geomorphology from Space' which you can find at: http://disc.gsfc.nasa.gov/geomorphology/GEO_2/GEO_PLATE_T-48.shtml  This shows lots of good imagery and gives you a basic explanation of the relief here.

Welcome to this blog

This blog accompanies the 5 lectures for Prelims geomorphology given by podcast by Heather Viles.  These lectures cover:

1. Introduction to geomorphology
2. Tectonics and geomorphology
3. Climate, climate change and geomorphology
4. Ecology and geomorphology
5. Mass movements and slopes

The posts on the blog will provide some more information and links to these and other key geomorphological topics.  I hope they are useful...