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The Q? Blog

Quarry Geology: Following a Volcanologist to the Field

by Adam Blankenbicker -- Jan 5, 2016
Photo of Adam Blankenbicker, a geology education specialist at the Museum

Adam is a self-proclaimed “volcanologist-turned-educator” who enjoys designing visitor experiences, especially around, you guessed it, geology. He has led...

Active pit at White River Quarry in Enumclaw, Wash. The dark rocks on the bottom are old basalt lava flows, and the upper, lighter layer is formed of more recent deposits of volcanic ash. Smithsonian photo by Don Hurlbert.
Active pit at White River Quarry in Enumclaw, Wash. The dark rocks on the bottom are old basalt lava flows, and the upper, lighter layer is formed of more recent deposits of volcanic ash. Smithsonian photo by Don Hurlbert.

I recently had the opportunity to travel with five geologists to unique sites around the country to understand more about the diverse geologic history around us. We were observing rocks and landscapes to reveal evidence of what happened in Earth’s past. Each of these geologic sites was located at an active rock quarry, which provided unobstructed views of large rock faces and samples that we could collect to look at more closely. Here is a brief story of what happened in Enumclaw, Wash., when Smithsonian Volcanologist Ben Andrews and I visited a quarry of volcanic rocks.

Ben Andrews using a hand lens to examine a rock. Smithsonian photo by Don Hurlbert.Ben and I arrived at White River Quarry and found a hole in the ground — well, that’s what I initially saw. The first thing Ben did was look closely at the rock face in front of us and notice that the top of the face was a lighter color sediment, made of volcanic ash. “It looks like explosive eruptions have happened here,” Ben was saying. “Just by looking at it like this we can’t say how old it is, but it’s above the darker rock, so it must have happened some time after those eruptions.” Those darker rocks, Ben said, were basalt, placed there by a series of fluid lava flows, probably millions of years ago according to geologic maps.

So we had already learned that this area had a history of explosive and passive (Ben likes the word “effusive”) eruptions. Volcanoes can change behavior over time, and when they go extinct, a new volcano may form nearby with a different behavior.Adam looking at ash and pumice in a boulder. Smithsonian photo by Don Hurlbert.

Ben and I walked around with some quarry employees and found rocks that helped form a more detailed story of this location. One thing that stood out were large boulders (photo at left) along the side of one of the roads – they were originally laying all over the property, but the quarry decided to move them because they were too soft to be useful. They are made of tuff (ash mixed with pieces of pumice). These could be evidence of a large pyroclastic flow (a large cloud of hot ash, gas and pumice that rushes down the side of a volcano).

During the flow, or after the flow was deposited and eroded, the boulders may have been carried here by a giant lahar (volcanic mudslide). About 4,600 years ago, there was a minor eruption at Mt. Rainier, only 38 kilometers (24 miles) away from this quarry. Although small, the eruption partially melted the glacier at its summit, causing a giant flood of water to rush down its slopes, picking up debris, rocks, and whatever else was in its path. This flow of volcanic material, a lahar, is like a rushing river of concrete. This event is known as the Osceola Lahar.

See volcanic rocks TUFF and BASALT collected from White River Quarry in the Q?rius Collection Zone. Get a printable poster about this quarry story. Get a Journey in Time through Quarries poster that shows five geologists and the geologic histories they explore.

Categories: Q?rius News, Field Notes
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