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Author Topic: What makes Lakes full of silt/mud or just pebbles?  (Read 3490 times)

Offline kora

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Hi dear Naked Scientists,

I noticed lakes in many North Scotland areas are nearby hills (no trees or forest usually, just low vegetation) and they are filled with rocks (rockbed) and pebbles. There is little mud in them. One can see the rocks below from the boat on good days.

But in England down south, and also in mainland Europe, lakes are way different. They are full of mud and clay or silt,and therefore visibility through the water is way less. When you walk into one, you don't walk on stones like you do in Scotland but on mud and your feet sink well into it, finding more soft surface and never a hard ground.

So my question is: what makes Scotland's lakes rocky and clear, and mainland Europe's /South England's so muddy? That is, what creates silt in some lakes, and no silt or mud in others?



 

Offline cheryl j

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Re: What makes Lakes full of silt/mud or just pebbles?
« Reply #1 on: 21/11/2013 16:32:21 »
I don't know about over there, but in North America, the Great Lakes were carved out by glaciers are mostly rock (limestone and granite) bottom. Lakes can also form from a rising mountain range. Some lakes are created when a river forms a snake like pattern and then high water makes a short cut through the center of it. Lakes can also form from sink holes. These would tend to have a sandy or clay bottom. I think all lakes tend to collect sediment and fill in, but the process is a lot faster in some than others.
 

Offline CliffordK

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Re: What makes Lakes full of silt/mud or just pebbles?
« Reply #2 on: 21/11/2013 23:54:06 »
It may have to do with the age of the lake, and certainly the geography around it.  There would always be a risk of lakes silting up.  But, that would also depend on how clean the water is flowing into the lake.

I know that Idaho has many rock slides that leave large boulders, at least on one side of the lakes.

As far as rivers, the fast flowing rivers in deep canyons in the western USA tend to have rocky bottoms.  The slow flowing rivers in the eastern USA often both have muddy bottoms, as well as muddy water.

If you are finding lakes with round pebbles, then likely the pebbles were made round from flowing water (or possibly glaciers), and the lake was dammed up due to some kind of a catastrophic event.  Water flowing into the lake would have to be relatively silt free, perhaps from steep rocky streams.
 

Offline evan_au

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Re: What makes Lakes full of silt/mud or just pebbles?
« Reply #3 on: 22/11/2013 17:09:00 »
Scotland was covered by glaciers in the last ice age.
This map shows the direction of ice flow which scraped the land bare, often carrying the soil out to sea, where it was dumped in undersea morraines (which can still be detected today - see map on page 4).

Some of these glaciers deposited the ground-up rock further south in England. Areas further from the sea (like Continental Europe or North America) have the ground-up rock deposited in what is now considered fertile farmland.
« Last Edit: 22/11/2013 17:19:46 by evan_au »
 

Offline OokieWonderslug

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Re: What makes Lakes full of silt/mud or just pebbles?
« Reply #4 on: 13/12/2013 16:16:23 »
The reason is most likely sediment rates. If there is no mud being washed into the lakes then there will be no mud in the lake. That would be because the soil is mostly covered with vegetation and therefore can't erode.
 

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Re: What makes Lakes full of silt/mud or just pebbles?
« Reply #4 on: 13/12/2013 16:16:23 »

 

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