17616472
Description
Mind Map by Blerta Morina, updated more than 1 year ago
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Created by Blerta Morina
over 5 years ago
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Rivers & Coasts: Formations
- Waterfalls &
Gorges
- They form where a river flows over an area of hard
rock followed by an area of soft rock. The soft rock is
eroded (by hydraulic action and abrasion) more than
the hard rock, creating a step in the river.
As water goes over the step, the soft rock is eroded
more and more and eventually, a steep drop is made
(a waterfall). The hard rock is undercut by erosion and
becomes unsupported and collapses. The collapsed
rocks are swirled around at the bottom of the
waterfall where they erode the soft rock (by abrasion),
creating a plunge pool. Over time, more undercutting
causes more collapses and the waterfall will move
back up the channel, leaving behind a gorge.
- They form where a river flows over an area of hard
rock followed by an area of soft rock. The soft rock is
eroded (by hydraulic action and abrasion) more than
the hard rock, creating a step in the river.
As water goes over the step, the soft rock is eroded
more and more and eventually, a steep drop is made
(a waterfall). The hard rock is undercut by erosion and
becomes unsupported and collapses. The collapsed
rocks are swirled around at the bottom of the
waterfall where they erode the soft rock (by abrasion),
creating a plunge pool. Over time, more undercutting
causes more collapses and the waterfall will move
back up the channel, leaving behind a gorge.
- Meanders &
Oxbow Lakes
- Rivers tend to be straight in the beginning. An
obstacle in the river may cause the river to divert to
one side. This causes erosion to one side of the river,
which leads to a further S-shaped motion of the
river, causing further erosion downstream and a
curved river channel.
- Over time, the neck of the meander will
narrow due to the erosion and the two
outside bends may eventually meet. The
river will take the new straighter, shorter
course, which makes the oxbow lake cut off.
- Rivers tend to be straight in the beginning. An
obstacle in the river may cause the river to divert to
one side. This causes erosion to one side of the river,
which leads to a further S-shaped motion of the
river, causing further erosion downstream and a
curved river channel.
- Deposition
- The river floods so it bursts its banks and so there is a loss of
energy. This means that the river can no longer carry the
material it was transporting and so deposition occurs and the
largest material is left behind first. This material is the reason
it begins to build up the banks at the side. This happens a
number of times and there is a build-up of layers of material
and so the levels get bigger and more apparent and formed.
- The river floods so it bursts its banks and so there is a loss of
energy. This means that the river can no longer carry the
material it was transporting and so deposition occurs and the
largest material is left behind first. This material is the reason
it begins to build up the banks at the side. This happens a
number of times and there is a build-up of layers of material
and so the levels get bigger and more apparent and formed.
- Interlocking
Spurs
- Upper course. Rivers aren't powerful
enough to erode laterally, so they
wind around the hillsides that stick
out into their paths on either side.
The hillsides that interlock with each
other, as the river winds around
them are interlocking spurs.
- Upper course. Rivers aren't powerful
enough to erode laterally, so they
wind around the hillsides that stick
out into their paths on either side.
The hillsides that interlock with each
other, as the river winds around
them are interlocking spurs.
- Levees
- Natural embankments along the river channel.
During a flood, eroded material is deposited
over the whole floodplain. The heaviest material
is deposited closes to the channel so, over time,
the deposited material is builds up, creating
levees along the edges of the channel.
- Natural embankments along the river channel.
During a flood, eroded material is deposited
over the whole floodplain. The heaviest material
is deposited closes to the channel so, over time,
the deposited material is builds up, creating
levees along the edges of the channel.
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