Friday, March 18, 2016

Bottle in the sand

Finding a bottle on the beach, or having someone else find one of my bottles, is straight-up exciting for me. The possibilities! So you can imagine my delight when I spotted a hint of glass poking up through the lower intertidal at a section of beach on the Elwha River delta. This particular location is one that I've been working at for almost 10 years, and has been rapidly eroding during that time. Here are some profiles and a time-series of beach position for this section of beach:

The time-series of beach position in this case goes back to February 2011 and suggests an average erosion rate of 2-3 meters/year...

I dug at the little hint of glass, which was sitting at the base of the active part of the beach, in the upper part of what we call the "low-tide terrace" this case a sort of low-sloping feature that is in the lower intertidal and is covered with large clasts and old rip-rap:

The red arrow marks the location where I was digging. Here is another perspective, with the location of the bottle mapped on to one of Andy Ritchie's PlaneCam orthos from 1 August 2015:

and zoomed in a bit:

and I was amazed to dig up a completely clean and unbroken Clorox bottle:

I used Clorox's great heritage bottle guide to date the bottle to 1951-1954. The bottle was actually lodged under a small boulder, but was surrounded by what appeared to be old lagoon sediments. Looking back at some of the historic imagery its clear that the final resting place for this bottle was probably the edge of "Beach Lake", a once-upon-a-time river channel of the Elwha, that transitioned into a lagoon, and over time has shrunk as the delta has eroded. Here is a map at the same scale as the zoomed August 2015 map above, but using an image from 1939:

and two others at the exact same scale from 1965:

and 1977:

Is it possible that this bottle was somehow discarded into this lagoon/lake, and was lost in the lagoon-edge muds for some time? Eventually in that scenario, the barrier started to erode, burying the bottle. Here is the image from 2000:

This image suggests that the bottle was probably lying underneath a few meters of sand and gravel as the beach retreated. The process is continuing. This winter has led to rapid erosion of that section of shoreline, exposing the bottle but continuing the process of making Beach Lake smaller. Between mid-February and mid-March another storm event overwashed the berm, knocking the elevation down and pushing beach sediment almost fully across Beach Lake:

and here is the overwash deposit from that event (or events?) that occurred between mid-February and mid-March of this year, with an outline for clarity: