VT--Lake Champlain's Tiniest Island
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Difficulty:
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Terrain:
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Size: 
(small)
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This is an earthcache. That means there is no container, but rather a geological lesson to learn. BYOP and a piece of paper/notebook and take notes (see logging requirements!) ENJOY!
Logging Requirements:
1. Please list the GC# / Name
2. Compare the size of Rock Dundar TODAY with the measurements in 1845 (see description below). If you are viewing the island from GZ rather than from a ferry or other boat, you will need some “measuring” estimating skill. See description below.
3. Compare the surface of Rock Dudar (light/dark; shiny/flat) with the rocks and dirt/sand near GZ. Based on your observations and the description below, what do you believe are the major geological differences? In other words, how does this island differ geologically from the rocks at your feet/the mountains behind you? These differences are the geological testimony to both different geological/hydrological actions AND ages of the rocks.
Lake Champlain is a remnant of the pre-historic, Lake Vermont (where you are standing now was under water!), a lake formed by glacial melting waters at the end of the last Ice Age. As the world continued to warm (think global warming), the glacial retreat actually created a gouge that connected the Lake to the St Lawrence estuary, thus making the lake (Champlain Sea) salty. If you look at the mountains and valley that are all around you, you should notice VERY rounded edges, since the glacial retreat severely eroded and weathered the geology of the area.
Rock Dunder and Juniper Island, both clearly visible ahead of you (you can even take one of the chartered boats, public cruises, or summer ferries near to it) are composed of shale, even though both the Adirondack mountains in front of you across the lake, and the Green Mountains behind you are made of much older bedrocks. Why you might ask? Well, the mountains are actually younger than the valley floor that is now part of the lake, and tectonic uplift (yep, earthquakes), pushed older bedrock over younger shale (formerly sedimentary deposits that had been metamorph’d.
As you already know, SHALE is composed of clay. This clay was deposited in Lake Vermont and has undergone the metamorphic process as the Green Mountains formed. This Utica slate once filled Lake Vermont (now Lake Champlain) from Shelburne to South Hero. Underwater, the shale caps older gneiss and limestone.
1845 SURVEY:
"Rock Dunder is a naked mass of slate, lying nearly midway between Pottier's Point, in Shelbume and Juniper Island. Its circumference, at the surface of the water, on the 28th of July, 1846, was 310 feet, and its height above the water 36 feet; but as there is considerable space around the base of the rock, near the water level, the circumference will vary with the amount of water in the lake. (needed quote to answer comparative question for #2)
Measuring the length of the island:
1) Take a pencil or other straight object and hold it at arms length. Mark the ends of the island on the pencil or stick.
2) Rotate to your left or right with your arm still outstretches until you see an object on YOUR SHORE that “measures” to the same points on your pencil/stick.
3) Go over to that object and measure it by paces.
References:
VanDiver, Bradford B. Roadside Geology of Vermont and New Hampshire. Missoula: Mountain Pub., 1987. Print.
Lake Champlain Basin Atlas. Web. January 01, 2013. .
"Rock Dunder - in Lake Champlain, Vermont - Places of Geologic Significance on Waymarking.com." Waymarking.com. Groundspeak, n.d. Web. 26 Jan. 2013..
"Full Text of "Guide to Lake George, Lake Champlain, Montréal and Québec [microform] : With Maps, and Tables of Routes and Distances from Albany, Burlington, Montréal &c."" Full Text of "Guide to Lake George, Lake Champlain, Montréal and Québec [microform] : With Maps, and Tables of Routes and Distances from Albany, Burlington, Montréal &c." N.p., n.d. Web. 26 Jan. 2013.
Www.lcbp.org. Lake Champlain Basin Program, 01 Oct. 2011. Web.
An unnamed guide who was telling a group of tourists about the “smallest island” when we visited the site.
Additional Hints
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