Wednesday, May 3, 2017

It's Water-Wise Wednesday with Frannie the Fish! [Awesome Aquifer Kit: Erosion and Weathering}

This week in Frannie’s exploration of the Awesome Aquifer Kit is all about the concept of erosion and weathering.

Photo credit: howtosmile.org
Weathering is the slow destruction or wearing away of soil or rock which is followed by the process of erosion, where the broken particles are then carried away.  This is a very important concept for groundwater and it can happen in two ways: mechanical weathering or chemical weathering.

Mechanical weathering is when rock or soil is physically broken down by constant exposure to flowing or moving water.

Imagine a river that’s moving quickly, picking up sand from the beaches and carrying it downstream.  That’s an example of the beach being mechanically broken by the stream, which carries the sand downstream and makes those beaches smaller.  The same thing can happen underground where, as water slowly flows and picks up particles of soil or rock, the land might get worn down and even sink slightly. 
 
Photo credit: USGS
If the sinking of the land occurs over a long period of time, we call that subsidence.

Chemical weathering is when the rock or soil mixes with the water and dissolves to become a new substance.

This usually happens when polluted rain seeps down into a carbonate type of bed rock.  The acidic water comes into contact with the basic soil and changes the chemistry of the rock so that it breaks down and forms new particles that move with the water flow.


Photo credit: ABC News
It is this kind of weathering and erosion that is usually the cause of sinkholes, a type of sudden natural disaster that results with a large hole in the ground.  Frannie will show us more about sinkholes next week.

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