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The Pinnacles EarthCache

Hidden : 06/02/2008
1.5 out of 5
1 out of 5

Size: Size:   other (other)

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Geocache Description:

The Pinnacles are yet another fascinating geological feature found at Crater Lake National Park


The process of their formation began around 7700 years ago with the cataclysmic eruption of Mt. Mazama. A pyroclastic flow, called Wineglass Welded Tuft by geologists, spread southward from the caldera and accumulated in many areas to depths of more the 100 meters. This flow was comprised of gas charged ash and pumice that was erupted in a zonal pattern. The striking vertical color variation that we see today is evidence of this chemical “zoning” within the magma chamber prior to the eruption. The lower lighter colored sections of the pinnacles were erupted first, and are comprised primarily rhyodacite pumice. The darker upper reaches of the pinnacles represent magma from deeper in the volcanic chamber and are made up of basaltic andesite scoria. Thus the exposed pinnacles that we see today show us the ‘inverted’ composition of the pre-eruption Mt. Mazama magma.

As this pyroclastic flow began to cool, escaping gases worked their way to the surface through fractures in this massive lava formation.

To claim this cache, you must answer the following questions via an e-mail to my profile.

    A. As the gases migrated to the surface, what happened to create these pinnacles?

    B. Other than Pinnacles what is another name for these magnificent spires?

    C. Why are they evident today?

Do not reveal your answers in your posted log.

Now for the FUN part: Although it's no longer required, why not post a picture of yourself or group with these amazing formations in the background?

Permission for this Earthcache was generously granted by the Chief of Interpretation and Cultural Resources of Crater Lake National Park because of the EarthCache ”Leave-No-Trace“ principles. Please respect the natural beauty and fragility of these geological wonders and confine your exploration of this area to designated trails.

Due to the tremendous amount of snow that blankets Crater Lake National Park each year, opportunities for visiting the Pinnacles is somewhat limited. To find out if the road to the Pinnacles is open check with park personnel or call 541 594 3100.

And the "FIRST-TO-FIND" honor goes to teamrakkasan!!

For more detailed information see the following references:

Additional Hints (No hints available.)