ACTIVITY 3: Deposition
Purpose:
To investigate in the lab the processes by which sediment grains
are eroded, transported and deposited by flowing water.
Notes:
The apparatus and materials needed are: a 1m length of guttering
(square section guttering is preferred) with two end pieces;
clean sand to fill the gutter to within 2cm of the top; rubber
tubing to connect to a lab. tap; container such as a large beaker
to put in the sink to catch any sediment washed over the end
of the gutter – preventing it from blocking the sink; small
pieces of gravel.
Development of knowledge and understanding:
This allows real sedimentary processes to be investigated in the
lab.
– sediment grains are visibly eroded, transported and deposited
in different ways. When these processes have been studied, the
study of the gutter can be extended by considering it as a simulation
of a river/sea situation.
Demonstration 3: Deposition - in the Stream
(This activity is based on ESTA’s “Second-hand Rocks”
in “The Science of the Earth 11-14” series.)
Learning objective:
To observe the processes of erosion, transportation and deposition
by flowing water.
The gutter provides scope for several investigations into the
ways in which sediment is moved in water. Set it up as shown and
turn on the tap gently.
- If you are the first to use the apparatus, notice what happens
to the water as it fills up the gutter.
- Once it is running uniformly, look carefully for places where
erosion is taking place. How is the sand being moved at these
spots?
- Study where the sand is being moved along the bed. This is
known as
“transportation” of the sediment. Exactly how is
it being moved?
- Find places where deposition is taking place. Are the newly
formed layers of sediment horizontal or inclined? How do they
build out into the pool at the end of the gutter?
- Try changing the flow rate and discuss any differences you
spot.
- Try adding a few pieces of gravel and study the flow around
them.
When you have finished, try to match the gutter work to modern
sedimentary environments and rock specimens. Would your investigations
enable you to say which way former currents flowed?
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