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The Afon Glaslyn, SnowdoniaCase Study of fluvial landforms and processes

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Introduction

The Afon Glaslyn, Snowdonia Case Study of fluvial landforms and processes All rivers aim to reach equilibrium so they are balanced and when they are in equilibrium from source to mouth a smooth curve is created called the graded long profile. However, as you can see from the diagram many rivers such as The Afon Glaslyn, do not acheive equilibrium and reach their graded long profile: Long Profile of Afon Glaslyn River with graded long profile Rivers become out of equilibrium when there is a change in base (sea) level. There can either be a positive change (rise) in the sea level or a negative change (fall) in sea level, resulting to a change in base level and a new graded long profile. Sea level changes happen because the Earth is in or out of glacial periods. Therefore sea level is changed either eustatically- a change in sea level due to a change in the amount of water locked up in ice sheets, or isostatically- when the the change in sea level is due to a change in the level of land caused by growing or retreating ice sheets. The change in base level affects the long profile of a river and as the river tries to reach its new graded profile in order to reach equilibrium there are various processes and landforms found along the river's course. ...read more.

Middle

Afterwhich some of the rock will be swirled around by river to form a plungepool. This can be seen in the diagram. Rapids occur when the layers of rock are thin and so there is no obvious break of slope. 4-6.5km * Processes The main process at this stage is deposition. The base level has decreased and in order to reach equilibrium, the river must deposit material to reach its graded profile. Base level may have decreased due to a change sea level or because the rock is soft and so it has been eroded down to much. However, deposition also happens because it lacks energy to carry load. * Landforms As the rock is below graded profile (eroded downwards) as lake has formed. Furthermore, as the flows into the lake, due to the lack of eneregy material has been deposited which overtime builds upwards and outwards forming a delta. . * Material size At these two sections material size is greatest as the sediment is made up of mainly large boulders as they have not yet been eroded with some clays and sands. Also, there are a large number of angular boulders and uneven beds in the upper reaches. Therefore, velocity is at its least because the small hydraulic radius increases friction and most of the energy is being used for erosion, traction and saltation. ...read more.

Conclusion

Velocity is higher than the upper reaches and so the amount od sediment transported is also higher. Lower reaches 14-16km * Processes Mainly erosian taking place because river above graded profile (base level decreased) so erodes to each equilibrium. * Landforms As there are erosional processes occurring in this section, it means that there are erosional features such as: rapids, potholes and gorges. The rapids and potholes are formed in the same way as in section 1. Gorges are formed as the process of the rocks collapsing (in waterfall process) repeats and as the water retreats upstream a gorge is formed. 16-25km * Processes The river is now below graded profile the process of deposition is taking place to reach equilibrium. * Landforms Landforms include floodplains, large meanders, braiding, pools and rifles-depositional features. 25-27km * Processes Now that the river is coming to the end and is nearing the sea it must deposit the load and therefore deposition is the main process. The bedload is deposited as sand and the suspended load deposited as mud. Also there is transportation in the form of solution and suspension. * Landforms The main landform created due to this deposition is an estuary. * Material Size By the time the sediment reaches the end of the river the material becomes the smallest it can get in a river because it has been eroded throughout the rivers course. ...read more.

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