Now head to station 12. Just past the bench, you will notice two large boulders, and if you look closely, a third covered in vegetation between them. Any idea how they got there? Without considering Union Bay’s history, I may suggest that they could be small erratics. An erratic is a large boulder that gets caught in a glacier, and is dragged with it as it advances or retreats. Ravenna Park, about 20 minutes away from UBNA, has a huge granite erratic potentially sourced all the way from Canada!
Both boulders looks like granite- an igneous rock (made from lava.)
Both boulders looks like granite- an igneous rock (made from lava.)
Speaking of glaciers, look out onto Union Bay and observe the landforms. The Seattle area is hugely influenced by past glacial movement, which carved out valleys and caused drumlins around Washington. On a clear day, you can see Mount Rainier. Rainier is actually a massive active volcano, and is one of the most dangerous volcanoes in the country if it erupts again. It last erupted over a century ago. It is 14,410 feet tall, and has 25 major glaciers on top of it. You can often also see the rest of the Cascades stretching out to the left of Rainier (6).
Post-glaciation, Ravenna Creek flowed out of Green Lake and deposited an underwater delta of sediment into Lake Washington. This flow stopped in 1911 with the lowering of Green Lake. When the Ballard Locks were created, Lake Washington dropped 9 feet, and exposed this delta, which would later become the site of University Village, the E-1 parking lot, UW playing fields, and UBNA. Because of this, the soil type of UBNA is made up of peat, or mainly organic matter from plant debris. This is the exposed delta- what you’re walking on used to be the lake-floor (7)!
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