Fraser River Estuary Earth Cache EarthCache
Hidden : 2/27/2014
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

British Columbia's estuaries are among the richest in the world. The largest estuary is formed by the Fraser River and is home to over 400 species of vertebrates, thousands of plants and a myriad of small invertebrates.

Estuaries are partially enclosed bodies of water along coastlines where fresh water and salt water meet and mix. They act as a transition zone between oceans and continents. An estuary has a free connection with the ocean. Fresh water input from land sources (usually rivers) dilutes the estuary's salt content.




There are five geological types of estuaries - coastal plain, bar-built, delta system, tectonic, and fjord. 

Coastal Plain – Millions of years ago, as ancient glaciers melted, some coastal streams and rivers became covered with water as sea levels rose. The Chesapeake Bay in Maryland and Narragansett Bay in Rhode Island are examples of coastal plain estuaries that were once river valleys.

Bar-built – Sandbars or barrier islands built up by ocean currents and waves in coastal areas created a protected area fed by small streams or rivers. The barrier islands off the Atlantic coastline of North Carolina and Massachusetts enclose bar-built estuaries.

Delta system – Deltas are formed at the mouths of large rivers from sediment and silt depositing instead of being washed away by currents and waves. When the river flow is restricted by the delta, an estuary may form. The estuaries at the mouth of the Nile River in Egypt and the Mississippi River in Louisiana are examples of delta systems.

Tectonic – Tectonic estauaries were created when a major crack or a large land sink in the Earth, often caused by earthquakes, produced a basin below sea level that fills with water. These types of estuaries usually occurr along fault lines. San Francisco Bay in California is an example of an estuary created by tectonics.

Fjords – Advancing glaciers ground out long, narrow valleys with steep sides. Then when glaciers melted, seawater flooded in. Glacier Bay in Alaska is an example of a fjord.

The Fraser River Estuary



The Fraser River delta formed as a result of two geological forces:

Tectonic: The area lies within a tectonically active region, with the Juan de Fuca oceanic plate converging with and subducting beneath the North American plate at this location. The resulting tectonic forces are responsible for the construction of the Coast Range Mountains, which provide source sediment for the Fraser River, and of the Georgia Basin, into which the Fraser River flows and deposits its sediment load, forming the Fraser River delta.

Glaciation: The area has been covered with ice sheets numerous times over the last few million years; the latest was the Cordilleran Ice Sheet during the Fraser Stade glacial epoch, between 25 000 and 10 000 years ago. These glaciers are responsible for sculpting the landscape, giving rise to the steep-walled Fraser River valley, and depositing thick layers of sediment on the valley floor and walls. Fluvial processes resulting from the flow of the Fraser River exert the third and most direct form of control on the development of the delta. The high flow velocity, water volume, and sediment load of the Fraser River as it merges with the Strait of Georgia have resulted in the formation of the modern Fraser River delta

Today the Fraser River has an annual flow of 112 cubic kilometers of water and discharge of 20 million tons of sediment into the Pacific ocean forming extensive Estuarine marshes, mudflats, floodplains, sloughs and river channels.



To Log this Earth Cache send an email (from our geocaching profile) with answers to the following questions:

1. What type of estuary is the Fraser River Estuary? Look out towards the west, describe what you see that helped you classify this estuary (note your ability to determine this may be affected by the tide level).

2. Look to the east and the west of the trail, describe the materials (rocks, earth, plants etc) extending in each direction. What are the differences between the compositions of each side?

3. What is the elevation at the closest point on the trail to the cache coordinates?


References:
National Estuarine Research Reserve System - http://estuaries.noaa.gov/About/Default.aspx?ID=215
Fraser River Delta, British Columbia: Issues of an Urban Estuary - http://geogratis.gc.ca/api/en/nrcan-rncan/ess-sst/7af6c9af-abb5-540f-8863-59af303959d0.html

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