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Washington Park Earth Cache EarthCache

Hidden : 12/08/2009
1 out of 5
1 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

The cache is traveler from the ancient past.

What is it, were did come from, how did it get there? They are not only found in the country side, they are located in towns as well.

A glacial erratic is a piece of rock that deviates from the size and type of rock native to the area in which it rests; the name "erratic" is based on the errant location of these boulders. These rocks were carried to their current locations by glacial ice, often over hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock (16,500 tons) in Alberta.

Geologists identify erratics by studying the rocks surrounding the position of the erratic and the composition of the erratic itself. Erratics were once considered evidence of a massive flood approximately 10,000 years ago, similar to the legendary floods described in the texts of ancient civilizations throughout the world. Ancient legends of an epic flood come from many cultures including Mesoamerican, Sumerian (Epic of Gilgamesh), Hebrew (Old Testament) and Indian culture. In the 19th century, many scientists came to favor erratics as evidence for the end of the last glacial maximum (ice age) 10,000 years ago, rather than a flood. Geologists have suggested that landslides or rockfalls initially dropped the rocks on top of glacial ice. The glaciers continued to move, carrying the rocks with them. When the ice melted, the erratics were left in their present locations.

"Peculiar," "irregular," and "uncommon," are words used to describe one class of Iowa rocks -- glacial boulders or "erratics." Geologists define erratics as stones or boulders that have been carried from their place of origin by a glacier and then left stranded by melting ice on bedrock of a different composition. In Iowa, glacial erratics are commonly observed where glacial deposits occur at the land surface, primarily in the north-central and northeastern parts of the state. In western and southern Iowa, erratics generally lie buried beneath wind-deposited silts (loess) that cover the glacial materials. In these areas, erratics generally are restricted to valleys, where streams have eroded through the loess and into the underlying glacial deposits.

The erratics seen in north-central Iowa are the most recent to arrive in the state. They are found on the Des Moines Lobe, the region last covered by glacial ice 14,000 years ago. The ice sheet entered Iowa from Minnesota and moved southward between what is now Mason City and Spencer, advancing as far as the capital city of Des Moines. This ice melted away about 12,500 years ago. Northeastern Iowa also has a significant concentration of boulders across the landscape, and the greatest number of exceptionally large erratics. This region, known as the Iowan Surface, was once much like southern Iowa, with loess deposits mantling steeply rolling terrain composed of glacial materials deposited in Iowa over 500,000 years ago. About 20,000 years ago, extremely cold climatic conditions led to erosional beveling of this area and removal of much of the finer-grained glacial materials, thus concentrating the larger pebbles and boulders at the land surface.

When these areas of the state were settled, farmers were forced to clear fields of the rock obstacles in order to plow and cultivate. Many of the erratics were used to build fences and foundations, while others were just piled along fence rows or into unused field corners where they are seen today. Clearing farm fields of glacial erratics is a necessary and frequent chore wherever glacial deposits are cultivated. Over time, seasonal freezes and thaws work these rocks upward from below the plow zone to the land surface. Smaller glacial erratics can be hauled out of the fields; larger ones are frequently blasted apart by dynamite and the pieces hauled away; while some of the largest are just left in place and avoided. At the municipal park in Nora Springs (Floyd County), an adjoining city street actually narrows to accommodate an erratic protruding into the right-of-way. Glacial erratics in Iowa are not difficult to identify. The vast majority are igneous or metamorphic rocks, rather than the usual sedimentary rocks of sandstone, limestone, dolomite, and shale that constitute the bedrock under most of Iowa. If you pick up a granite rock, composed of interlocking crystals of pink feldspar and glassy quartz, you can be sure it is not native and that it came from outside the state, most likely carried by glacial ice.

Most glacial erratics appear worn and rounded, and sometimes include beveled or faceted surfaces. During the course of their journey, the rocks were jostled against other erratics or scraped against the underlying bedrock, rounding off corners and planing smooth surfaces, eventually producing their characteristic appearance. Glacial transport also caused some boulders to fracture, producing fresh angular edges. Rocks carried by rivers also undergo abrasion and become rounded in the process. In fact, most of the igneous and metamorphic rocks in Iowa's river valleys were originally transported into the general area by glaciers, then eroded from the glacial deposits and moved some additional distance by a river.

Transportation by glacial ice, however, produces some other features unique to this mode of travel. The most easily observed of these tell-tale signs are glacial striations, a series of parallel lines or fine grooves gouged across the beveled faces of erratics or inscribed on the underlying bedrock surface. .

To receive credit for this Earthcache, you will need to complete the following three tasks:

1 Describe to me the way the surface of this erratic feels. (Is it rough, smooth, etc?) Describe the color and texture of the minerals in the erratic. Don't Describe it in log. Email me the answers.

2 Tell what the design on this rock looks like..

3 When logging this Earthcache, please upload a picture of yourself/team with the erratic in the background and have your GPS clearly visible. (See Example above)

I'd like to thank Paul Huting of the City of waterloo allowing me to develop this Earthcache in Valley View Park

Additional Hints (No hints available.)