Oregon Dunes EarthCache

The Oregon Dunes are a unique area of windswept sand that is the result of millions of years of wind, sun, and rain erosion on the Oregon Coast.

The sand in the Oregon Dunes comes from the Coast Mountain Range, which is sedimentary rock that was uplifted 12 million years ago. As the rock was moved downstream by the coastal rivers, it tumbled and abraded itself into sand.

Oregon's shoreline stabilized about 6,000 years ago. Tides, wave action and strong coastal winds moved sand up to 2.5 miles inland for thousands of years. This area of dune development rests on a gently-sloping terrace of solid marine sandstone called the Coos Bay Dune Sheet. This low rock surface stretches for 56 miles from Heceta Head to Cape Arago which differs from the steep headlands found on most of the Oregon coastline which prevent inland movement of sand.

Winds are a major influence in dune formation. Summer winds blow steadily from the north and northwest at 12-16 miles per hour. Mountain barriers near the coast deflect wind currents, sculpting the sand info many different shapes.

In winter, winds are generally lighter; however, they can exceed 100 miles per hour during intense winter storms. These winds blow from the south and southwest moving large amounts of sand. Seasonal changes in wind direction reshape dune sculptures and ridges.

Water influences dune formation. Strong ocean currents flowing north in winter and south in summer hold sediment from rivers near the shore. Currents, tides and wave action dredge sand from the ocean floor and deposit it on the beaches where the wind takes over.

Sand absorbs and stores a large part of the annual rainfall. Where winds have removed sand down to the water table, plants have flourished. In the wet winter, the rising water table creates marshy areas with standing water several feet deep. With the upward pressure of water, the sand grains become more saturated and may float, resulting in quicksand. Look for quicksand in low, unvegetated areas between the dunes.

Wind and water are the two strongest forces shaping dune formation. Summer winds blow steadily from the north and northwest at 12 to 16 miles per hour. Mountain barriers near the coast deflect wind currents, sculpting the sand into many different shapes. In winter, winds vary more; however, they can exceed 100 miles per hour during intense winter storms. These winds bow from the south and southwest, moving large amounts of sand. Seasonal changes in wind direction reshape dune sculptures and ridges. Strong ocean currents flowing north in winter and south in summer hold sediment from rivers near the shore. Currents, tides and wave action dredge sand from the ocean floor and deposit it on the beaches where the wind takes over. Sand absorbs and stores a large part of the annual rainfall. Where winds have removed sand down to the water table, freshwater plants have flourished. In the wet winter, the rising water table creates marshy areas with standing water several feet deep. With the upward pressure of water, the sand grains become saturated and may float, resulting in quicksand.

The Oregon Dunes are the largest expanse of coastal sand dunes in North America. Spend some time in the dunes, you are sure to see geology in action!

Here, the desert-like landscape blends with lakes, rivers, ocean and forest, creating a diverse ecosystem filled with plants and animal. Day to day, season to season this ecosystem can change dramatically.

Location

Requirements

Send the owner the answers to the following via email:

• State the noise regulation on the sign at the posted coordinates.
• What are the 2 main forces that create a Dune.
• Briefly describe how the sand got there.
• Estimate the height of the dune you are standing in front of.

Bonus question just for fun:

Sources

1. US Forest Service Website: http://www.fs.fed.us/r6/siuslaw/recreation/tripplanning/oregondunes/geology/geology.shtml

2. Wikipedia http://en.wikipedia.org/wiki/Oregon_Dunes_National_Recreation_Area

3. Oregon Department of Geology and Mineral Industries website: http://www.oregongeology.org/sub/learnmore/Placestosee/SandDunes.htm