Battle Ground Lake: "Maar"ed Landscape EarthCache
Battle Ground Lake: "Maar"ed Landscape
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This Earthcache will direct you to Battle Ground Lake State Park. The cache site is at the water’s edge but there is no need to get wet. Take an easy stroll downhill from the day use lot to the lakeside, and onto the dirt trail that wraps around the lake. The park closes at dusk. Please note there is now a $10 one-day Discover Pass fee to use the park, unless you're willing to take a shot at the 15-minute parking spaces and dash to the lake and back (not recommended, but I'm not your mom).
The Battle Ground area was named for a battle that settlers at Fort Vancouver expected to happen in 1855 between U.S. Army soldiers and some Klickitat Indians. The post commander allowed the Indians to leave the fort on the promise that they would return after burying their chief, who had been accidentally killed. The battle to get the Indians to return never occurred, because the Indians returned peacefully to the fort, true to their word, but the name "Battle Ground" stuck anyway.
Until Oregon State made its Crater Lake at Mt. Mazama famous, Battle Ground Lake was known as Crater Lake to Washingtonians.
Battle Ground Lake is a volcanic feature known as a maar. It’s formed when magma rises from below, through what’s called a diatreme, which is a fancy word for a volcanic pipe that pushes up through other innocent, unsuspecting rocks. This magma moves up beneath groundwater, sneaks up on it, and with a wicked gleam in its eye, taps the groundwater on the shoulder. The groundwater, having no head for panic, flashes into steam (which is rumored to have a head) and causes the rock overhead to explode upward with terrible force.
The crater that’s left over afterward is usually shallow, with a flat bottom. Maars can be anywhere from 200 to 6500 feet across, and from 30 to 650 feet deep. Battle Ground Lake, for instance, is only 60 feet deep at its bottom, owing to millennia of silt deposits, which are estimated at around 2000 feet thick. If you scuba to the bottom (the park does allow scuba in the lake) and reach into the silt, you can actually reach back in time, if only a little ways. These craters usually fill up with water and form natural lakes, as this maar did here in Battle Ground Lake.
Why does this lake fill up? It’s fed through the diatreme below, which connects it to an aquifer (an underground geologic layer, usually sand, gravel or other water-permeable rock, which stores water). A estimated one million gallons of water flow through the lake every day, dispersing through fissures in the rock to other bodies of water close by. This was discovered during the 1980’s when a St. Patrick’s Day experiment began with green dye being released deep in the lake. Over the next hours and days, green-dyed water was found in a few local wells, as well as streams and creeks, outside the park boundaries. Because of the steady flow of water from the aquifer, the lake’s surface differs only 12 to 18 inches during the changing seasons of the year.
If you’ll notice on your way into the park, you have to drive up a hill; once you park you have to walk down the other side of it. This would be true from any ground approach to the lake because in fact, the lake is surrounded by a doughnut-shaped (or annular) hill. The original contents of the lake’s crater, including the space now occupied by 2000 vertical feet of lake sediments, were blasted out to form this hill.
The term for the rock that’s blasted out is tuff. Tuff is ash, rock, and mineral bits that get blown onto the surrounding landscape from both the magma tube (that diatreme again) and the unsuspecting overhead rock.
In any case, most of the rocks you‘ll see around the crater will be volcanic in nature; they used to be solidified parts of the volcano’s innards (sides of the diatreme tube, for example). But some of the tuff is made up of the original surface rock, which the steam explosion blew through.
To complete this Earthcache, do the following:
1. Guess at the area of the lake’s surface, in acres, OR estimate the distance across the maar at water level, from where you stand to the far side, in feet. Put this in an email to me, not your log.
2: Look around on the ground or in the shallow water. Do you see any gravel-sized rocks of a “typical” volcanic color? What color are they? Choose one and compare its weight to a gravel-sized rock of a distinctly different color (you may want to bring one from home to ensure it is not volcanic). Is the lake rock heavier or lighter? Please remember to leave the rocks where you found them when you are done. This answer also goes in your email, not in your log. Logs that contain answers will be deleted without notice.
3: Submit a picture of yourself/ your group and your GPS with the small volcanic boulder at the coordinates.
Sources: U.S. Geological Survey and U.S. National Park Service Website, 2006, "Geology in the Parks", Tilling, 1985, Volcanoes: USGS General Interest Publication, Washington State Parks Website, 2001, Anthony Vinson Smith, "Portland City-Search" Website, January 2001, Washington State Parks and Recreation Website, 1999 , Washington State Parks Battle Ground Lake Website, 2007.
Frumious Jane is the author of the Caching Out geocaching mystery series, written under the name Morgan C. Talbot.
Additional Hints
(Decrypt)
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