David Williams describes how Magnolia got its name in his new book, "The Street-Smart Naturalist: Field Notes from Seattle."
"A 22-year-old Navy lieutenant, George Davidson, who visited the area in 1856 while leading a U.S. Coast and Geodetic Survey trip, thought the trees blooming on the edge of the hill were magnolias," he explains.
They weren't, and still aren't. The trees are madronas, and calling them magnolias is as accurate as - dare it be said? - comparing apples (of the rose family) and oranges (of the citrus family).
Magnolia is well known as the site of Perkins Lane, with its houses that once sat high above the water but now touch Puget Sound. This unfortunate loss of property is caused by sediments left behind when the land that became Seattle sat beneath 4,000 feet of glacial ice.
Geologists know that a great sheet of ice once covered the Puget Sound region between 15,000 and 13,650 years ago. Williams writes that this was "the last of at least six periods of glaciation over the last 2 million years." This same ice sheet covered nearly all of Canada at the same time.
The era of glaciers is responsible for three major layers of rock deposited atop each other. At the bottom are the "mocha-to-cappuccino-colored silts and sands known as the Olympia beds," Williams writes. On top of the Olympia beds is the Lawton Clay, a fairly impermeable sediment deposited when Puget Sound was a freshwater lake.
As time marched on and the continental glacier leaving Canada reached our neighborhood, "Rivers continued to wash out of the glacier but now they deposited sands and silts over the filled-in lake in broad swaths across the landscape," Williams explains.
This layer, which can be up to 300 feet thick, is called Esperance Sand. The interplay between Esperance Sand and Lawton Clay is what causes Seattle's sliding land. Geologists recognize the instability of Esperance Sand.
Williams explains: "When wet, the Esperance acts like a giant sponge, soaking up water that gets trapped atop the underlying, impervious Lawton Clay."
Soil strength is thereby reduced and allows the sand to glide or slip across the clay, "sending cliffs, mud, trees, houses, bridges and cars downslope." Usually the sand creeps slowly down to the Sound, but movement can be much quicker when above-normal precipitation occurs, as in the winter of 1996-97. That's when we get "catastrophic landslides."
The contact between Esperance Sand and Lawton Clay occurs all over Seattle, but its most dramatic occurrence is at Perkins Lane in Magnolia.
Landslides have been reviled during Seattle's history, and for no uncertain reasons. What happened in 1996-97 wasn't unusual or unexpected - at least for geologists and local historians.
For the rest of us, the slides were quite a surprise. Torrential rains generated eight slides, damaging around 50 homes along Perkins Lane and sending "five once-permanent houses and the road next to them cascading to the Sound."
The cause for this landslide was a "weakness in the rock deposited by the glacier passing over Seattle," writes Williams.
Williams records in his book that, "When owners of some of these houses (on Perkins Lane) sued the city, King County Superior Court judge Kathleen Learned ruled against them, stating that "It is no small thing to re-engineer the basic geology of the region, which is what the plaintiff's position would lead to."
Glaciers and geology had spoken.
- Peter Stekel
Readings
David Williams will be reading from 'Street-Smart Naturalist' at Bailey/Coy Books on Capitol Hill on July 27; at Green Leaf Books, which is at the south end of Stone Way near Gasworks Park, on Aug. 16; and at Queen Anne Books on Aug. 20. Visit the Web at www.streetsmart-naturalist.com for more information.[[In-content Ad]]
