Planes of Travertine
Like Rome, Seattle was built on seven hills. Both cities also share a building stone: a type of limestone known as travertine. Coincidentally, most of the travertine used in Seattle buildings came from quarries in Tivoli, about 20 miles east of Rome. These quarries provided stone for the Colosseum and St. Peter’s Colonnade in Rome, as well as the Getty Center in Los Angeles, the best-known travertine-clad building in this country. All the rock from the quarries formed less than 200,000 years ago with a peak around 80,000 years ago, making this some of the youngest stone in the building trade.
This is an earthcache! As such there is no container to find - instead in order to claim this cache as found you'll need to read the description, make observations at the posted coordinates and send your answers to the questions below to the CO!
Travertine Formation
Unlike the Salem Limestone at GCAKAHW, travertine does not form in the sea. Instead, it precipitates from calcite-rich water expelled from springs or in caves. A modern example is Yellowstone National Park’s Mammoth Hot Springs, where hot water rises through cracks and emerges in pools. When this occurs, the calcite in the water settles and accumulates layer upon layer. It can occur so quickly that a half-inch thick bed can form in a single year. In contrast, marine-deposited limestone takes thousands of years to deposit a single inch of calcite.
An example of how travertine limestone forms!
The stone panels in front of you are the bedding plates, the area where the calcite accumulated. Small honeycombs are visible in many of the panels. These holes were once gas bubbles, which were coated so quickly in calcite that they turned to stone. If you look at the side – or edge – of the panels, you can see bedding plates. Seattle builders used travertine plenty both indoors and out, but what makes this location unique is the style of bedding plane panels. Traditionally panels are cut perpendicular to the bedding plane resulting in panels that look a bit like layered Swiss cheese, whereas at this location the panels were cut parallel to the plane. This allows us to see the gas bubbles and a singular layer of the deposition plane in an uninterrupted manner!
As you look directly at the face of the building, you're looking at a single deposition plane. If you look around the corner (left of this photo) you'll see a transverse look at multiple planes!
Logging Requirements
In order to log this earthcache, please make observations at GZ and then answer the following questions to the best of your ability and then send your answers to the Cache Owner.
- Look at the edge of the panels (face north around the corner of the above image) are the depositions perfectly straight or wavy? Why do you suppose this might be?
- Look at the front of the panel (face west) do you see any gas bubbles? How large are they?
- In colder climates the honeycomb gas bubbles in travertine are often filled with a filler material in order to prevent erosion. Are the honeycombs here filled in?
- Why do you suppose this decision was made?
- Take a photo of yourself, your geocaching name, or a personal object in front of the building and attach it to your found it log!
References:
- Williams, David B. "Seattle Walks: Discovering History and Nature in the City." University of Washington Press, 2017.