Nisqually Delta Earthcache
What is a delta?
A delta is a landform that is formed at the mouth of a river
where that river flows into another larger body of water. Deltas
are formed when the sediment carried by the river is deposited as
the flow leaves the mouth of the river. Over time, this deposit
builds the characteristic fan-shaped pattern of a river delta.
River deltas form when a river carrying sediment reaches a body
of standing water, such as a lake, ocean, or reservoir. As a river
flows through its stream bed, it picks up and suspends particles.
When the flow enters the slower, standing water, it is no longer
confined to its channel and expands in width. This flow expansion
causes the water to slow down, reducing its ability to carry
sediment and retain it in suspension. As a result, the sediment
drops out of the stream flow and deposits. Over time, this single
channel will build delta or fan-shaped deposit with smaller a web
of streams coursing through it, pushing its mouth further body of
water. As the delta builds, the slope of the river channel
decreases because the river channel is longer but has the same
change in elevation. As the slope decreases, the river channel
becomes unstable for two reasons. First, water under the force of
gravity will tend to follow the path of least resistance down
slope. During a flood it will break through levees because of its
instability and spill out onto a new course with a shorter route to
the body of water, thereby obtaining a more stable steeper slope.
Second, as its slope gets lower, the amount of stress on the stream
bed will decrease; resulting in sediment being deposited in the
channel, raising the channel bed relative to the floodplain. This
makes it easier for the river to breach its levees and cut new
channels to enter the body of standing water at a steeper slope.
When this happens, some of its water can remain in the former
channel. These channel switching events occur in a mature delta
building a distributary network.
Why is it important?
Most river deltas, the Nisqually included, form an
estuary. Estuaries form a transition zone between fresh water river
environments and ocean environments and are subject to both marine
influences, such as tides, waves, and the influx of saline water;
and riverine influences, such as flows of fresh water and sediment.
The inflow of both seawater and freshwater provide high levels of
nutrients in both the water column and sediment, making estuaries
among the most productive natural habitats in the world.
Nisqually Glacier and Headwaters.
The Nisqually River Delta is fed by and the end of
the Nisqually River that starts its 81 mile journey in southern
Mount Rainier National Park. It is fed by the Nisqually Glacier on
the southern side of Mt Rainier. It flows west along the
Pierce-Lewis county line, then northwest through the foothills,
forming the boundary between Pierce and Thurston counties. It
traverses the Nisqually Indian Reservation along its lower 10 miles
and flows into the Puget Sound approximately 15 miles east north
east of Olympia.
To get credit for this Earth Cache, please answer
the following questions.
1. Estimate the width at the widest part of the
Delta at the posted coordinates.
2. What sign is posted at the posted
coordinates?
3. How many stream channels can you se entering the
sound?
I highly encourage posters to submit a photo with
their log. It is a beautiful view and is ever-changing.
I recommend you check tide tables before attempting
this one.
Congratulations! to Acyducy and Buckley Boy on the
Co-FTF.