Little Black - The Meandering River EarthCache
Little Black - The Meandering River
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Difficulty:
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Size:  (other)
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The Little Black River or Rivière Noire in French has its headwaters in the boundary mountains located just west of the Quebec/Maine border. The river flows an east/southeast path down hill across the border, reaching a flat valley before it finally flows into the St John River. While the watershed is only 261 square miles the path that it has taken indicated that something unusual happened here in the past. According to researchers this is where a section of the glacier finally came to rest a little more then 11,000 years ago. As the last ice age came to a close the land was barren and covered with a thick layer of glacial till. As the last bits of the grounded glacier quickly melted it released huge amounts of water that headed down hill toward the ocean. The water took the path of least resistance often changing pathes as it eroded the river banks or became blocked by ice.
In contrast to braided rivers, meandering rivers typically only contain one channel that winds its way across the floodplain. As the water flows, it deposits sediment on banks that lie on the insides of curves (point bar deposits), and erode the banks on the outside of curves. The river will become a braided river once that it has reached the threshold level of sediment load or slope is reached. The main controlling factor on river development is the amount of sediment that the river carries, once a given system crosses a threshold value for sediment load it will convert from a meandering system to a braided system. In this case the threshold was never reached in this short section of river, due in part to it rate of flow carrying the load down stream as it travelled. The channel that is formed is highly mobile, with the river layout often changing significantly during flood events. Channels move sideways via differential velocity: On the outside of a curve, deeper, swift water picks up sediment (usually gravel or larger stones), which is re-deposited in slow-moving water on the inside of a bend.
In this case of the Little Black River it flowed down off the mountains located to the northwest until it reach this flat-bottomed valley. In flat areas, the flow of the river slows down, allowing the soil carried in the river to settle out in a process called deposition. The speed of the flow in the river varies wherever it goes around a bend, causing the riverbed to meander (follow a winding path) as it crosses areas that are mostly flat. Sometimes a long meander is cut off from the stream's regular flow of water, and a crescent-shaped lake is formed. Such a lake is called an oxbow lake due to the distinctive curved shape that results from this process. These will fill with silt and dry up leaving a unique landscape.
This earthcache will take you by paddle along a section of the river where you will be able to see the difference between the gravel making up the south and north sides of the river channel and you should be able to answer a question about the channel formation. Remember this is an earthcache, so there is no container - just an earth science lesson at a beautiful natural area along the river. To log this cache, you should be able to see the layering of the gravel making up the banks of the river. Email me through my profile the differences that you can identify between the north and south river banks at the posted coordinates and estimate the distance that the river will have to cut before a new channel is formed. In your email please include the name of the earthcache and the number of people in your group in your email. Please take the time to describe what you found that was special about the location so that others might have the same experience. It also would be nice if you would post a photo so others would know what they have to look forward to at this earth cache.
You may want to look at the area using either Google Earth or Google maps.
If you enjoy this earthcache you may want to check the Maine Geological Survey located at (visit link)
They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.
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