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A V-shaped valley, a U-shaped valley, a dune, a delta and a stack each name the carrier that made them and say whether it cut or built.
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In this lesson you read four landforms on a drawn skyline before any of them is named, and then find the rules you were using. By the end you will be able to say from a landform's shape what shaped it — a river, ice, wind or waves — and whether it was cut by erosion or built by deposition, and to do it whether or not the maker is still there.
You know that weathering breaks rock, that water, wind, ice and gravity carry the pieces, and that each carrier drops its load where it loses energy. This lesson is those three ideas seen from a distance: the shapes that cutting and dropping leave on a whole landscape, and how to read them backwards to the carrier that made them.
A landform is any shape on the land's surface. A V-shaped valley is a river's; a U-shaped valley is a glacier's. A dune is a ridge of wind-blown sand; a delta is the fan a river builds where it meets the sea; a stack is a pillar of rock left off a cliff by waves; a moraine is the unsorted heap a glacier drops. Sorted sediment is all one size, which water does; unsorted is every size mixed, which ice does.
A skyline is drawn with four landforms on it, from left to right: a narrow notch whose sides meet at a point, with a stream running down from the point; a much wider gap with a flat floor and steep straight sides; a row of low crescent-shaped mounds of sand; and a flat fan spreading out into the water at the edge.
Before reading on, decide for each one: was it cut into the land or piled onto it? And what did the cutting or the piling — running water, ice, wind or waves? Write your four answers down with a reason for each.
Two of the four are holes and two are heaps, and the reason you gave for the wide flat-floored gap is the one most worth checking. A stream is running in it now; but a stream cuts downwards and makes a notch, not a floor half a valley wide. Something else made that shape, and the stream moved in afterwards. That is the whole of this lesson: the shape is the evidence, and the maker need not still be there.
Every carrier of sediment cuts the land in its own way and builds in its own way, so a landform's shape says which carrier made it and whether it was made by taking material away or by piling it up.
Rivers cut downwards, at the bottom of the channel, so a river valley is a V: narrow at the stream, opening out upwards. Where a river slows — at the sea, or on a lake — it drops its load in a flat fan: a delta.
Ice fills a valley from side to side and grinds the whole width, so a glacial valley is a U: a flat floor and steep straight sides, often with a small stream wandering along it that arrived after the ice had gone. Where the ice melts it drops everything it was carrying at once, boulders and clay together, in an unsorted heap: a moraine. Water sorts what it drops by size; ice never does, and that is how the two are told apart.
Wind carries sand and builds it into dunes: ridges with a gentle slope the sand was blown up and a steep slope it slid down.
Waves cut into headlands from both sides until an arch forms and its roof falls, leaving a stack; and they roll pebbles up a shore and leave them as a beach.
To read a landscape, ask two questions of each shape: who made it — the V or U, the sorted or unsorted heap, the crescent — and was it cut or built — a hole is erosion, a heap is deposition. The maker need not be there any more. A U-shaped valley in a country with no glaciers is still a glacier's valley.
Another way: picture
A skyline with four shapes, each with a small drawing of its maker beside it. A narrow notch with a stream at its point and a river drawn beside it; a wide trough with a flat floor and a glacier drawn filling it from side to side; a row of crescent mounds with a wind arrow; a fan at the water's edge with a slowing river spreading over it. Under the two valleys the word cut; under the mounds and the fan the word built.
Another way: steps
To read a landform:
Every valley is given to the water running in it. A stream in a U-shaped valley did not cut it; a glacier did, and the stream moved in after. The shape says who cut it, and a river's shape is a V.
A wide valley is taken to need a big river. Width is not a river's doing. Rivers cut downwards; only ice grinds sideways across a whole floor.
A heap is read as a hole. A dune, a delta and a moraine were piled up, not cut. Ask whether material was added or removed before deciding erosion or deposition.
The maker has to be present. It does not. A landform outlasts what made it, sometimes by millions of years, and reading a shape whose maker has gone is exactly what the skill is for.
On a coast, a beach of rounded pebbles all much the same size lies below a ridge of boulders, gravel and clay mixed together.
Two heaps, differently sorted.
The pebbles are one size and rounded: dropped by water, which sorts, and rolled by waves. The ridge is every size at once: dropped by ice, which does not sort.
Sorting names the carrier.
So the ridge is a moraine from a glacier that reached this coast long ago, and the beach is what the waves have made since. Both were built; neither was cut.
In chalk hills, a narrow V-shaped valley runs down to the plain with no stream in it at all.
A river's shape, and no river.
A V is cut by running water and by nothing else, so water ran here once — when the ground was frozen and rain could not soak into the chalk.
The shape outlasts the maker.
Now the rain soaks straight in and the valley is dry, but it is still a river valley, and its shape is the evidence.
Each landform on the left was shaped by one of the carriers on the right. Sort them. Some carriers made more than one.
| a river | ice | wind | waves | |
|---|---|---|---|---|
| a deep valley with a V-shaped cross-section and a stream at the bottom | ||||
| a wide valley with a flat floor and steep straight sides | ||||
| long ridges of sand, gentle on one side and steep on the other | ||||
| a fan of flat muddy land where a river meets the sea | ||||
| a pillar of rock standing in the sea off a cliff | ||||
| a ridge of boulders, gravel and clay all mixed together across a valley mouth |
The picture is a landscape drawn as a skyline, with four landforms on it. Mark a feature made by deposition rather than erosion.
This task has no paper form; do it on a device.
Three landforms are described. For each, name what shaped it, and say whether it was made by erosion or by deposition. First: a fan of flat, muddy land spreading out where a river meets the sea. Second: a field of long ridges of sand with a gentle slope on one side and a steep slope on the other. Third: a wide valley with a flat floor and steep straight sides, like a U.
| what shaped it | erosion or deposition | |
|---|---|---|
| first | ||
| second | ||
| third |
A valley high in the mountains has a flat floor half a kilometre wide, steep straight sides, and a small stream wandering along the middle of the floor. What shaped the valley?
Each landform on the left was shaped by one of the carriers on the right. Sort them. Some carriers made more than one.
| a river | ice | wind | waves | |
|---|---|---|---|---|
| a deep valley with a V-shaped cross-section and a stream at the bottom | ||||
| a wide valley with a flat floor and steep straight sides | ||||
| long ridges of sand, gentle on one side and steep on the other | ||||
| a fan of flat muddy land where a river meets the sea | ||||
| a pillar of rock standing in the sea off a cliff | ||||
| a ridge of boulders, gravel and clay all mixed together across a valley mouth |
A photograph taken from orbit round another planet shows a network of narrow valleys that branch and join downhill like the branches of a tree, ending at a wide flat plain. There is no liquid water anywhere on that planet's surface today. What does the shape of the valleys say?
Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.
The picture is a landscape drawn as a skyline, with four landforms on it. Mark the feature built by the wind.
This task has no paper form; do it on a device.
You can read a landform's shape as evidence of what made it. Say out loud how you tell a river's valley from a glacier's, and a heap dropped by water from one dropped by ice, and why a valley with no water in it can still be a river's. That closes the two units of this course: a rock, a column of strata and a landscape are all records of processes nobody watched, and you can now read all three.