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Climatic Controls of

Holocene Erosion of

The Lesser Himalayas

http://media.eurekalert.org/release_graphics/Geo_1.jpg

http://en.wikipedia.org/wiki/Geology_of_Nepal

The lesser Himalayas are the mid-section of the HimalayasShown in reddish colors on the map below:

http://www.pnas.org/content/107/12/5317/F1.large.jpg

Area of investigation: The Indus Water Shed The Indus Delta

http://www.lib.utexas.edu/maps/middle_east_and_asia/india.gif

Area of investigation:

Factors that control the rate of erosion in the Indus Delta Area:

• Steep slopes• Tectonic plate

movement• Sparse

vegetation• Water –

Glaciation and High rain fall

• Monsoons

http://hunzatimes.wordpress.com/northern-areas-photo-gallery/indus_river_from_karakouram_highway1/

Steep slopes Tectonic converging plates push land masses

together breaking lithosphere into blocks causing thrust fault mountains

GravityPulls downward on mountain slopes causing it to

become harder to build mountainTaller mountain = greater gravitational forces (friction)

FrictionBlocks sliding over one another create friction wearing

or breakdown of material

http://www.geo.arizona.edu/Antevs/ecol438/crust_05.gif

http://www.geo.fu-berlin.de/fb/e-learning/geolearning/en/mountain_building/weathering/Erosion3/index.html

Water (solid or liquid)Always runs toward base level

creating friction (erosion) Tectonic uplift causes river

bottom to rise adding energy to the system

http://www.geo.umass.edu/structure/analog_models/Erosion_MountBuilding.pdf

Glacial movementNew snow accumulates causing ice to flow down slope, friction grows between ice and rock, rock is

destroyed and carried by the river down slope

http://www.geo.umass.edu/structure/analog_models/Erosion_MountBuilding.pdf

Geologists believe the uplift of the Tibetan Plateau (23 to 10 million years ago) intensified the monsoon

climate for the Himalayas

Topography plays an integral part in rainfall along mountainous regions. This is enhanced during monsoon seasons.

http://asaa.asn.au/publications/ac/2008/asian-currents-08-06.html

http://en.wikipedia.org/wiki/File:India_climatic_zone_map_en.svg

Monsoons and Erosional processes:

Oct – FebWinter sun retreats South. The land mass cools rapidly air pressure builds over the North causing cold air to descend and sweep down from the Himalayas. Dry winds blowing from the Northeast creating arid conditions. Giving way to desert, dry shrub and sparse vegetation.

Rain and Lack Of…

http://web.mst.edu/~rogersda/umrcourses/ge301/what%20is%20a%20100%20year%20flood.htm

June – Sept.Moist wind blows in from the Southwest. The Himalaya Mountains act as a high wall blocking wind from passing into central Asia. Warm moist air rises causing a drop in temperature causing monsoon storms and precipitation.

http://readerfeedback.labs.wikimedia.org/wiki/File:India_southwest_summer_monsoon_onset_map_en.svg

Monsoon Season:When rain migrates far into the mountains and reaches regions shielded by orographic barriers large winds and huge amounts of precipitation on arid desert landscape increases debris flows and erosional hill slope processes increasing sediment evacuation.

The largest erosional feature

for the lesser Himalayas

http://www.geog.ucsb.edu/~bodo/pdf/bookhagen05_amy_nw_himalaya.pdf

Recall: Water Runs Down Slope carrying large amounts of sediment with it.

In this case into the Indus River Delta

http://www.geo.umass.edu/structure/analog_models/Erosion_MountBuilding.pdf