19 October 2011

LIFE AND DEATH OF A SEA STACK

1890

   
Jump-off Joe was a 100-foot-/30-meter-tall sea stack near Nye Beach, Oregon—named because visitors had to jump off its steep side to get around it.

Before the 1880s it was still attached to the mainland. Around 1890 its connection fell away. From then until World War I it was a well-known tourist attraction.

These undated postcards show part of its lifecycle.





According to Historic Photo Archive:

The rock formation was subject to rapid erosion and returning visitors would make a point of checking out the changes since their last visit... The arch finally collapsed during a severe storm in late January, 1916.

Or not. The following photographs, courtesy of the USGS, suggest that Jump-off Joe survived as an arch at least until 1920, then in ever-diminishing incarnations until the 1990s. (H/T Irish Weather Online.)

1910

1920

1970

1990

  
As an interesting aside—near my home in northern California there are a few old uplifted sea stacks that now stand high and dry on coastal terrace.

Photo by tuolumne tradster via Flickr.



  
These ancient stacks bear areas of highly-polished mirrorlike rock, which have have been analyzed by archaeologists using scanning electron microscope and atomic force microscope, then compared with wave polish from cliffs below the terrace, with elephant rubs, and with just about every other form of rock polish. 

Their conclusion: woolly mammoths rubbed here. 

From the paper: 

In eastern and southern Africa, rubbing stones are relatively common in the savanna and grassland areas. They stand as monuments to ancient itches... Stack 1 in our study area is adjacent to a [freshwater] seep which has probably been active throughout the Pleistocene. The modern Asian elephants and African elephants especially like to rub on trees and rocks after wallowing in mud. Ectoparasites encased in the drying mud are removed by the rubbing action which benefits the animals. It is possible that the seep was an animal wallow which encouraged the use of the adjacent rocks, and caused their high polish over a matter of perhaps a hundred thousand years.

Mammoth rubbing rocks. Photo: © Julia Whitty.


  
The paper:

  • E Breck Parkman, et al. Extremely High Polish on the Rocks of Uplifted Sea Stacks along the North Coast of Sonoma County, California, USA (pdf).  

Woolly mammoth at the Royal British Columbia Museum. Photo: WolfmanSF via Wikimedia Commons.
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