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Half Dome the Bornhart EarthCache

Hidden : 10/21/2014
1.5 out of 5
4.5 out of 5

Size: Size:   other (other)

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Geocache Description:

Boneharts are distinct steep-sided domes. These geomorphologic features are made up of relatively unjointed masses of rock that have developed a dome shape from exfoliation as the surrounding rock is eroded away.

As you embark or continue your journey to discover and explore beautiful and historic rocks, waterfalls, peaks, creeks and other wonders, please keep in mind that these places need to remain wild and protected so that they may be enjoyed by others for generations to come. Please be diligent in respecting these sites by doing the following:

  • Please keep trash with you at all times, do not leave it behind in these pristine places.
  • Bury human waste 6 inches deep, make certain you are at least 50 paces away from any water source and PLEASE bring your toilet paper and sanitary items back out with you.
  • Keep food and all scented items on your person at all times.
  • Support wildlife by allowing them to find their own food, do not feed them.
  • Allow plants to grow and water to stay clean by staying on trails, bike paths and roads.

Thank you, Yosemite Wilderness Management

This EarthCache can be reached from a number of different trailheads. The hike in from any of them is significant and requires adequate preparation. A Half Dome permit is required, but the coordinates are on the sub-dome . Staying overnight in the Yosemite Wilderness requires a permit.

Half Dome is a bornhart. A bornhart is a distinct steep-sided dome often with a flattened top. The few joints that are present are close to parallel to the steep sides of the dome. Some references suggest that only igneous and metamorphic rocks form bornharts, but they can be of any rock type and are found in a wide range of environments.

Bornharts and inselbergs (Tor – Joshua Tree NP are sometimes used interchangeably or bornhrts are described as a type of inselberg. However, these two terms are used to describe different aspects of similar landforms, so there can be some overlap. Inselbergs emphasize the isolated nature of the landform and bornharts have a domed top. Thus there are bornharts that are not inselbergs, and inselberts that are not bornharts.

In general, bornharts form from the erosion of weaker material from around them. There are a variety of reasons the surrounding material are weaker including (but there could be others):

  • A higher density of jointing;
  • A weaker rock;
  • An uneven bedrock surface.

The dome shape of the bornhart is created by exfoliation. Exfoliation is an erosional process that cracks the rock along the surface due to the decrease in pressure on the rock as the overlying rock is eroded away (The Other Half of Half Dome – Exfoliation

Logging requirements: Send me a note with:

  1. The text "GC5F8HY Half Dome the Bornhart" on the first line
  2. The number of people in your group.
  3. Compare the shape of Half Dome to the definition of a Bornhart. Does Half Dome really qualify as a Bornhart?.
  4. Does the Sub-dome qualify as a Bornhart?.
  5. Identify one other Bornhart that you can see from the coordinates (not Half Dome).

The above information was compiled from the following sources:

  • Twidale, C.R. 1995. Bornharts, Boulders and Inselbergs. Caderno Lab. Xeoloxico de Laxe Coruna. Vol. 20. pp. 347-380.

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