Yellow Bluff, Au Pair extraordinaire! 🌎 EarthCache
Hidden : 5/20/2019
Difficulty:
2 out of 5
Terrain:
2 out of 5

Size: Size: other (other)

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Geocache Description:



For purposes of logging this cache you must answer the following three questions:
1) Looking up at the bluff what percentage of the cliff is represented by each of the 4 lower layers of sediments? (Bottom to top: Whidbey Formation, Peat layer, glacial deposit layer, and top soil?
2) Compare the amount of sand at WP1 beach to the WP2 beach. Which beach benefits the most from Yellow bluff’s abundant sediments? What does that imply about the two drift cells located in front of the beaches and longshore current direction? Can you guess which is divergent,(traveling away from each other,) and which is convergent, (traveling toward each other.)?
3) What do you think is the cause/origin of the bluff’s yellow color?
4) You MUST upload a picture of you or a personal item at WP2 and either send it to me via the message option or attach it to your found log.



 An earthcache is the magical combination of geocaching and geological discovery. They vary greatly from traditional geocaches in that there is NO PHYSICAL CONTAINER! Once at the Earth Cache site, take in the scenery, the geological marvels or oddities, and read the cache description. You will likely be asked to answer some questions about the site and optionally take a picture. You can email the cache owner or use the Message Center to send answers to the required questions. Please don’t be intimidated about answering the questions. They are not graded and were meant to enrich your visit, open your eyes and provide you with new knowledge and insights about the location. Most importantly have fun!

This earthcache is located on Skagit Land Trust Property and placed with permission.

Gazing up at these amber, majestic, towering, cliffs may generate mild feelings of awe or wonder. But to a geologist these are a diverse piece of a complex puzzle. The puzzle pieces all fit together to tell a story about the dynamic processes shaping the shoreline of Guemes Island and influencing all creatures that live here.

Before we get into the present let’s delve a bit into Yellow Bluff’s past. A living laboratory of ice age geology: Yellow Bluff is a beloved outdoor geology classroom. Many layers of time are represented here! Yellow Bluff exposes a remarkable sequence of sediments that span the earth’s history from before the last ice age. These sediments underlie much of northern Puget Lowland, but are best exposed right here, at Yellow Bluff.

At the base of the bluff, the Whidbey Formation represents one of the best exposures of sediments that accumulated in the lowlands between glaciations. The Whidbey Formation includes sand, gravel, peat, volcanic ash, and organic sediments that separated two ice age glaciations of Puget Sound. Dark, thick peat is located at the top of the Whidbey Formation sequence. The peat and organic beds host a number of fossils that record the climate and environment of this period. Overlying the organic beds are glacial deposits that record the passage of the last great ice sheet from Canada. They include sand and gravel deposited by the advancing glacier. This layer is topped by a poorly sorted mixture of sand, silt, and rocks called “till” that is deposited beneath the glacier itself. On top of the entire bluff is sediment that was deposited beneath the glacier as it retreated north and floated in the rising sea. Eventually the land rebounded from the weight of the ice and lifted these sediments above sea level to where they are now.

And now to the present.

Sources of sand

Not only can Yellow Bluff be classified as a feeder bluff, a term that describes the source of sand and gravel that “feed” nearby beaches, but it also is labeled by a grander name, “feeder bluff – exceptional.”! (By the numbers, some 15 percent of the Puget Sound shoreline qualifies as “feeder bluffs” while only 2 percent is rated “exceptional.”) Knowing that some sand and gravel is lost to deep water, scientists now recognize that ongoing erosion from shorelines is essential to maintaining healthy beaches. Beaches fall into the class of accretionary shore forms. Other formations in this category can be spits, or other low-angle, non-rocky shoreline features. These have also been referred to as “drift babies” because they are products of drifting sediment and, in geologic terms, they can never grow old! Drift babies cannot persist in their natural condition without a steady supply of nourishment from the sediment source within their drift cell. So in essence Yellow Bluff is a nurse bluff!

Sand and gravel migration

Two key questions to ask about any beach: Where are the sands and gravels coming from, and where are they going?” A major force at work on beaches today is wave action, which tends to dislodge sands and gravels where waves come ashore. Each incoming wave nudges the sediment along. On a beach, more powerful waves result in greater sediment movement, often called “drift.” A drift cell is a section of shoreline in which sand and gravel naturally move to create beaches. If nine out of 10 storms come from the south, the net drift will be to the north. Sands and gravels may move along a beach for miles before finding a place of deposit. Yellow Bluff feeds two littoral “drift cells”; one goes north and the other Southeast, where sediment is moved by waves and currents along the shoreline. The drift cells drop their sediment on beaches along the west shore of Guemes Island and along the Guemes Channel shoreline. As storm cycles intensify, the beaches built and maintained by these drift cell processes act as a natural barrier, helping to mitigate the exposure and flooding impact to waterfront properties and unique wildlife habitat. The sediment from Yellow Bluff maintains the ecological values of that beach and backshore.
EDUCATIONAL LOGGING REQUIREMENTS

In order to substantiate your visit and comply with the educational requirement for Earth Caches you have to submit your answers to the following questions to the cache developers via their profile:
For purposes of logging this cache you must answer the following three questions:
1) Looking up at the bluff what percentage of the cliff is represented by each of the 4 lower layers of sediments. (Bottom to top: Whidbey Formation, Peat layer, glacial deposit layer, and top soil)
2) Compare the amount of sand at WP1 beach to the WP2 beach. Which beach benefits the most from Yellow bluff’s abundant sediments? What does that imply about the two drift cells located in front of the beaches and longshore current direction? Can you guess which is divergent,(traveling away from each other,)and which is convergent,(traveling toward each other,) ?
3) What do you think is the cause/origin of the bluff’s yellow color?
4) You MUST upload a picture of you or a personal item at WP2 and either send it to me via the message option or attach it to your found log.



Please keep in mind the following when visiting Yellow Bluff:
• Access to the beach is using a pre-existing steep ramp and may involve climbing over drift logs. Use with caution and at your own risk! The access point may not be appropriate at this time for people with physical disabilities or for very young children. Round trip distance to The Bluff and the beaches is a little over 1 mile.
• Similar to other natural areas, please keep your pet on a leash.
• Please do not build fires.
• UAVs or drones are prohibited.
• Please note that during extreme high tide parts of the beach may become inaccessible making a return trip difficult and hazardous.
• The boundaries of Skagit Land Trust's conservation area are marked. The beach and uplands beyond these points are private. Please respect our neighbors' private property.

Credits:
Jon Riedel of North Cascades National Park,
http://www.skagitlandtrust.org
http://www.coastalwatershedinstitute.org/blog/?p=169
https://fortress.wa.gov/ecy/publications/publications/1406016.pdf
http://explorebeaches.msi.ucsb.edu/sandy-beach-life/sand-movement
https://nwstraitsfoundation.org/wp-content/uploads/2016/12/GiPAC_11192016.pdf

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