unit seven: variation in glacial processes, landforms and landscapes over different timescales Flashcards
what are 3 time scales to examine how glacial landforms change over time
rapid, seasonal and long-term
how can glacial landscapes change rapidly?
mass movement such as rockfall
what is rockfall?
rapid, free-fall of rock from a steep cliff face. activated by freeze-thaw weathering, loosening the exposed rock
what is an example of where scree slopes can be found in the uk?
nant ffrancon valley in snowdonia
where did the randa rockslide take place?
switzerland
when was the randa rockslide?
april 18th 1991
what happened during the randa rockslide?
- around 15 million m3 of rock slid down the valley
- it was caused by intense freeze-thaw weathering
- total of 33 million m3 of rock fell 600m
- changed the profile of the valley in less than a day
- 33 buildings destroyed
- blocked a 1.3km-long stretch of vispa river
what are fluvioglacial streams like in the summer?
more meltwater = bigger streams
what are fluvioglacial streams like in the winter?
less meltwater = smaller streams
how can fluvioglacial streams change daily?
impacted by the direction of the slope is facing, because facing towards the sun will result in bigger streams
what do seasonal variations impact?
processes of transport and deposition vary
what are 2 landforms where seasonal changes to fluvioglacial streams affect deposition?
- infilling of lakes as kettle hole lakes
- infilling proglacial lakes with varves
how do varves form?
- winter = less meltwater = smaller clay and silt pieces
- summer = more meltwater = bigger pieces (finer material in suspension while big are deposited)
what can varves tell us?
1) age
2) climate (how much sediment was deposited)
why do varves occur?
changes in meltwater and velocity
what ultimately may happen to kettle hole and proglacial lakes after a number of years, if varves continually form?
they will get filled with sediment and will slowly stop being a lake
what are alluvial fans?
deposits of stream load at the base of a steep slope
how do alluvial fans form?
- streams flow down the mountain areas with a lot of energy, due to steep gradient
- carry large amounts of sediment
- lower altitudes on flatter ground = velocity of stream is reduced = loss of stream energy
- as stream fans out it creates the familiar triangle-shaped feature
what is an example of an alluvial fan in the uk?
beneath cwm coch in the nant ffrancon valley in snowdonia
what is the apex of an alluvial fan?
the narrow point of the alluvial fan
what is the fan apron of the alluvial fan?
the wide triangle
how big is koshi river’s, in nepal, alluvial fan?
15,000 km2
how are ribbon lakes infilled?
as the stream enters the lake, its velocity drops, resulting in the stream load being deposited
what is a misfit stream?
the running water that drains the post glacial landscape will converge at the base of a glacial trough
how does a misfit stream alter the shape of a glacial trough?
cuts downwards due to vertical erosion
what is an example of a misfit stream?
the afon ogwen through the nant ffrancon valley
