GY1004 TEST WEATHERING SOILS AND LANDFORMS Thursday 17 February BENNETT F75B11:30 AND 12:05 See 1 st year notice board

The test on Thursday is compulsory. If you miss the test for good cause (e.g. medical reasons or personal problems), you must submit either a self-certification form (available from the general office) or a medical certificate from your doctor to be eligible to sit the test at a later date. If you are absent without good cause and/or do not self- certificate or provide a medical certificate from your doctor, you will not be allowed to sit the test at a later date and you will be awarded a mark of zero. If you do miss the test for good cause, it is your responsibility to seek an opportunity to sit the test at a later date. Failure to do so will result in a mark of zero. I will not chase students who miss the test on Monday, whatever the reason.

GY1004 Principles of Physical Geography B Lecture 9 Uplift and denudation DEPARTMENT OF GEOGRAPHY

Uplift

Causes of uplift Orogenic uplift – uplift associated with active tectonics Eperiogenic uplift - uplift without significant folding and faulting

Measurement and estimation

Rates of orogenic uplift Minima Alps and Himalayas m Ma -1 ( mm ka -1 ) Southern Tibet 2000 m Ma -1 Himalayas, Andes 5000 m Ma -1 ( mm ka -1 ) Maxima Southern Alps 10,000 m M a -1 New Zealand(=10,000 mm ka -1 or 10 mm a -1 ).

Rates of orogenic uplift

Rates of eperiogenic uplift Colorado Plateau, USA 100 m Ma -1 Deccan Plateau, India 15 m Ma -1 Florida, USA 20 mm a -1 (unsutsainable) Europe after glaciation mm ka -1 15,000 BP5-10,000 mm ka -1 Current5-20,000 mm ka -1

Summary Orogenic uplift Minimum rates m Ma -1 (Alps, Himalayas) High rates – 5,000 m Ma -1 (Southern Tibet) Maximum rates – 10,000 m Ma -1 (Southern Alps New Zealand) Eperiogenic uplift Typical rates – m Ma -1 (Deccan and Colorado Plateaus) All averaged over several million years

Agents of erosion Mass wasting Water Wind Ice Himalayas

Global fluvial denudation rates SourceMt a -1 Total mechanical denudation15,000 Total solute denudation2,200 Total denudation17,200 = 116 t km -2 a -1 = 43 mm ka -1 Excluding areas of internal drainage= 61 mm ka -1

Deriving rates of fluvial denudation River sediment loads; Reservoir sedimentation; Marine sedimentation; Dating surfaces of known erosional age. Results are representative of progressively longer time spans

Long term rates of fluvial denudation Minima c. 1 m M a -1 Maxima > 5000 m M a -1 These are similar to range of estimates of present day denudation rates. Radiometric estimates for Cenozoic era (65 Ma BP) in regions of subdued relief of 30 m Ma -1 are not incompatible with a global average of m Ma -1.

Uplift and denudation, New Zealand

How high can a mountain become? RangeCrest widthCrest height S. Alps N. Zealand80 km3,000 m Himalayas350 km7,500 m S. Alps Himalayas

Summary Denudation is the lowering of the land surface by erosional processes. In most terrestrial environments, the action of water dominates the removal of weathered products.

Summary The mean global denudation rate is about 61 mm per thousand years. Mechanical denudation is by far the most important, contributing 85% Solution contributes 15%.

Summary Denudation rates are controlled by several factors including climate, relief, basin size, lithology and anthropogenic impacts. Maximum rates of orogenic uplift and denudation lie between 5000 and 10,000 mm ka -1. Rates of crustal uplift and denudation in young mountain ranges are approximately equal, reflecting the achievement of a steady state.

Learning outcomes revisited These lectures have explored how the planetary systems of the atmosphere and lithosphere interact to determine the character and nature of the earths surface. It has concentrated on how tectonically created land surfaces are modified by surficial processes. Of particular concern have been the processes by which rocks at or near the earth surface are broken down into a mantle of waste called regolith (weathering), the transformation of regolith into soil (pedogenesis) and the processes which cause the erosion of the earths surface (denudation). We have also considered the geographical distribution of soils and landforms at the global scale.