Seasonal Ups and Downs

— from Bea vonTobel —

Back in the early 60s when I was first exposed to geology classes, we learned about the “rebound theory.” For those parts of the world that had been glaciated, an interglacial period meant that the great weight of the ice had been lifted, and land masses began to rebound. Coming from that part of Ohio that had been covered, traveling into Upper Canada and the maritimes, living and hiking in the Adirondacks, we were subjected to miniscule though constant readjustments in elevation.

Later in life, as a pilot, aeronautical charts were annually updated with notations as to MSL (mean sea level) and AGL (above ground level), which served as warnings as to how close to terra firma we actually were.

Coming to Orcas in the late 80s and later serving as the airport manager here, I came to know intimately the official elevation of the Orcas airport: 30 feet MSL.

The FAA, in all its wisdom, has never noted seasonal variations in elevation. As a daily observer of airport environs, I could visually ascertain these seasonal variations. Looking north from my office window, I could see differences in the changing perception of Sucia, just 3 miles offshore. I noted that during the months of May-September, Sucia appeared higher when I stood on the spot on the runway which served as the official 30’ mark. From late September to late May, the water distance to Sucia appeared to be less because Sucia appeared lower.

Drawing upon my old geology knowledge, I figured that smaller islands, perhaps not so well-anchored as larger land masses, must be subject to seasonal elevation variations. From my vantage point at the top of Mt. Constitution, my weekly observations from May through September also appear to point out this variation. (And, perhaps the extreme numbers of people who drive to the top, thus adding much more weight during the Saturday weekly observations I make, exacerbate the summertime island-wide appearance of sinking.)

As a result of my observations, I generally cautioned pilots to be certain to adjust their altimeters carefully, and to tap the glass cover to make certain all possible elevation errors had been eliminated before flight.

We are now into September, one of the critical readjustment months for the island. We can only hope that as time moves forward, Orcas Island does not become so seasonally affected that we arise annually from the mists of the sea, much like Brigadoon.

Tap the glass on your barometer, as your elevation may vary.