Author: David B. Williams

Singing Stones

Summer solstice often elicits strange stories about Stonehenge. Now we learn that the builders of the ancient site may have chosen their building material for the simple reason that they were musical, with they meaning both the rocks and the builders. In a recently published article in Time and Mind: The Journal of Archaeology, Consciousness, and Culture, researchers Paul Devereux and Jon Wozencroft propose that the bluestones used in Stonehenge were transported more than 125 miles for their acoustical quality. The bluestones, a collective term for dolerites, rhyolites, and tuffs, come from the southwest corner of Wales. The area is known as Mynydd Presell and is famous for the rocky outcrops known as carns.

The study grew out of Devereux and Wozencroft’s work looking at how our senses might have influenced our relationship to landscape. What they found is a visual connection between the natural outcrops and numerous man-made structures, particularly dolmens. When they turned to sound, they discovered that the Welsh bluestone was a “noteworthy soundscape” filled with many ringing rocks. They propose that it is “highly improbable” that the Neolithic stone masons were “unaware of the echoes and the sonic characteristics of many of the rocks around them.” Unfortunately, when they tried to test the bluestones used at Stonehenge they met with little success, primarily because the stones were set in the ground and concrete, which tended to dampen the sounds. Despite this situation, they are hopeful that their work will encourage others to further the study of lithophones, or rocks used deliberately for their sound qualities. For more information, you can read an article in the New York Times.

I was very excited to read this study as I have long been intrigued by the sounds of stone. I first encountered this phenomenon in southern Utah with the Navajo Sandstone. Walking through the petrified dune field of the Navajo, I periodically came across gray rocks that rang when I stepped on or kicked one. The white or red layers of the Navajo lacked this quality. I eventually found out that the gray layers were ancient playa deposits, preserved as limestone lenses within the sandstone. Like the bluestone, the limestone was very dense. And since the rock often weathers out into boulders, they were in a perfect space to produce sound with plenty of air around them for resonance.

Another time I noticed ringing rocks was at the Getty Museum in Los Angeles. The complex is covered in thousands of three-inch thick panels of travertine, which comes from quarries in Tivoli, about 20 miles from Rome. Best known for its use in the Colosseum, the 80,000-year-old rock is a type of limestone that forms in hot springs. I discovered the sound qualities of the Getty travertine during a visit while I was working on my book Stories in Stone. About half way through my tour, I rapped one of the panels and was startled by its tone. The travertine is very dense but these panels also ring because of how they are mounted. Each panel is bolted about three-eighths of an inch away from each surrounding panel and from its concrete backing. The builders did this so the panels could move when the next earthquake hits. As with the Navajo, the air space allows the stone to resonate and because every panel at the Getty is different, each one produces a different sound. Pretty cool, I think.

Whether the ancient builders of Stonehenge actually chose the bluestones for their musical qualities is not terribly important or life changing. What is important though is that the researchers took the time to observe and to consider the bigger picture of our relationship to the world around us. When we do this, we may not hear songs, but I suspect we will have richer lives.

Oso landslide and Seattle

The Oso landslide is a true tragedy, in part because as news reports have noted, study after study showed the dangers of the slope. It was steep, undermined by the river, made of unconsolidated sediments, and further weakened from above by clear cutting, which allowed water to permeate more easily into the hillside. We can only hope that this horrible event will encourage developers, home owners, and government officials to reconsider where they build and to establish more thorough regulations.

As many others have written, landslides are wide spread in this region, including Seattle. This is a fact that has long been known. Consider the letter written on February 27, 1897, by Seattle’s City Engineer Reginald Thomson to Corporation Counsel John K. Brown, the lead attorney for the city. Thomson wrote that landslides had occurred in Seattle “from a time to which the memory of man runneth not back.” The reason had to do with the intraction between a layer of impervious blue clay that lay at the base of the land and pervious glacial drift atop it. When it rains, wrote Thompson, water percolates through the drift “in devious ways” until it reaches the clay below, resulting in a “condition of saturation and suspension” that continues until “the surface ground breaks and settles down.”

Modern geologists refer to Thomson’s drift as the Esperance Sand, a layer deposited 17,400 years ago during the last ice age when a 3,000-foot-thick glacier passed over the region. The clay is known as the Lawton Clay, a rock unit deposited in advance of the sand. As Thomson noted, when it rains water penetrates the sand until it reaches the impermeable clay and in effect lubricates it and makes the slope susceptible to sliding.

A "typical" Seattle hill, From Tubbs

Confirming Thomson’s observation, a recent study found that more than 1,400 landslides had hit Seattle since 1890. These included high bluff peeloffs, groundwater blowouts, deep-seated landslides, and skin slides. Skin slides, which are small and can be triggered by intense rainfall, are the most common. Deep-seated events are the most destructive; one of the best known in recent years was on Perkins Lane in Magnolia, when part of the bluff slid and carried several houses down to Puget Sound. The slide occurred in January, by far the worst month for sliding with almost three times more than the next nastiest months, February and March. Not coincidentally, November, December, and January receive the most precipitation.

(When owners of some of these houses sued the city, King County superior court judge Kathleen Learned ruled against them stating: “It is no small thing to re-engineer the basic geology of the region, which is what the Plaintiff’s position would lead to.”)

Usually fairly small and localized, landslides reveal the weak spots in the landscape, the places one might not want to build. This is one reason that green spaces such as Interlaken, Frink, Carkeek, and the Duwamish Greenbelt became parks and not home sites. But we have rewritten the story line, ignoring the historic reluctance to build on clearly less-than-stable slopes. More than 85 percent of the recorded slides owe their slippage to human created problems, include building improper drainage, not repairing broken pipes, chopping off the toes that protect slopes, and imprudent pruning of stabilizing vegetation. Many of the landslides that have hit since 1890 would probably have occurred in geologic time but with human activity we have fashioned a new time scale, one based on human time. In doing so we have made landslides more relevent to the city’s topography and to those who live here.

If you want to find evidence for slides and future slides, go to any steep hillside around the city. Look for areas mostly bare of shrubs or trees, such as the east side of Magnolia above the Magnolia bridge, which slid in 1997; areas rich in springs and seeps, evidence that water has percolated down to the Lawton Clay and is following gravity to the surface; areas covered in alders and maples, trees that pioneer unstable terrain; and areas with askew stairs that look as if they were made by a drunk contractor but which indicate ground movement. (Technically the hill is slumping and not sliding but it is still not a good sign. You can also see this in the tree. On a slumping slope, the trees either till backward or curve up at the bottom.)

Fortunately, the City of Seattle does recognize the high potential for landslides and has developed maps indicating particularly susceptible areas. But then such maps also existed for Oso. We need to do a better job at paying attention. The signs are there. Let’s hope we can learn from Oso.

Landslide zones in Seattle