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Mt. Hood View Earthcache

A cache by PathfinderMark Send Message to Owner Message this owner
Hidden : 01/24/2010
Difficulty:
1 out of 5
Terrain:
1 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:


As an earthcache, there is no “box” or “container” to discover. Rather, with this cache, you discover something about the geology of the area. For more info, consult www.earthcache.org

This earthcache is on the corner of SE Kelso Rd. and SE Richey Rd. in rural Boring, OR. It is about a 15 minute trip from I-205 (Sunnyside exit).


Geology:

Mt. Hood, a volcanic mountain in the High Cascades chain is visible over the nearby fields. The entire High Cascades province is characterized by a north-trending belt of upper Miocene to Quaternary volcanic rocks that were erupted on the east margin of the upper Eocene to Miocene Western Cascades province. The late Pleistocene record of this volcanic activity is well preserved on the crest of the High Cascades. In other words, the rocks that form the Cascades were placed there relatively recently, making these mountains “young” in comparison to many other mountain ranges. If you look at a map, you can see that there are a series of mountains that are part of this High Cascades platform – Mount Hood, Mount Jefferson, Three Sisters, and Mount Mazama (Crater Lake) to name a few. These volcanic centers have been responsible for major eruptions and flows of pyroclastic material. The pyroclastic material has been a variety of rock types – basalt, andesite, dacit, and rhyolite to name a few.


History:

Mount Hood can still be considered a potentially active volcano! Mt. Hood has erupted at least twice in the past 1,500 years, the most recent major eruption being sometime just prior to 1805-1806 when Lewis and Clark visited the region.


On October 29, 1792, British Lt. William Broughton, under the command of George Vancouver, identified and named the peak after Lord Samuel Hood a respected admiral of the British Royal Navy.

1805-1806 – Lewis and Clark – in their expeditions of discovery into the west their journals and maps mention Mt. Hood on several occasions between November of 1805 and April of 1806. Overall, they appear fascinated by the snowy peaks of this volcanic chain, though it is unclear whether they understand the magnitude of what they have discovered.

There is a great map that highlights their volcanic mountain discoveries: http://vulcan.wr.usgs.gov/LivingWith/Historical/LewisClark/Maps/map_volcanoes_lewis_clark.html

1859, 1865 – minor eruptions lasting a few hours were viewed by W.F. Courtney (1859) and a soldier posted at Fort Vancouver (80 miles away) (1865).


Volcanoes provide a variety of dangerous conditions.

  • Bombs – These are rocks that are expelled from the volcano. They usually fall rather close to the volcano itself.
  • Pyroclastic Flow – Fluidized masses of rock fragments and gases that move rapidly in response to gravity. Pyroclastic flows can form in several different ways. They can form when an eruption column collapses, or as the result of gravitational collapse or explosion on a lava dome or lava flow. The flow is fluidized because it contains water and gas from the eruption, water vapor from melted snow and ice, and air from the flow overriding air as it moves downslope. They flow very quickly sometimes at a rate of over 100 mph. The Hazards Zonation map shows the areas most likely to be affected by this type of flow.
  • Lava Flow – these flows of molten rock are expelled from a volcano by a non-explosive effusive eruption. A great example of this is the Hawaii volcanoes. While destruction can be great, they move slowly and systematically.
  • Lahar – Volcanic mudflows that may be started by an eruption event. They travel quickly (up to 60 mph) and have been know to travel 190 miles from their source. They are the consistency of concrete – fluid when moving, but solid when they stop. The Hazards Zonation map shows shows times of estimate arrival of this type of flow in surrounding towns. (this type is the most likely to affect the greater Portland area).
  • Tephra (Ash) Fall / Acid Rain – Technically, Tephra is any of the rock material tossed into the air by an explosive volcano. Tephra is not typically immediately dangerous but can lead to climate cooling, additional snowfall, and acid rain.


 

Dangers to Portland:

The most likely widespread and hazardous consequence of a future eruption would be for lahars (rapidly moving mudflows – mixed with melted snow) to sweep down the Sandy/Zigzag and White River valleys towards Portland. Lahars are typically caused by hot volcanic flows that melt the snow and ice that then push sediment and rock in the madly rushing liquid flow down the river valleys. Lahars can also be caused by landslides that are loosened during and eruption.

Lahars can be up to 100 vertical feet “deep” and thus cause massive destruction to dams and the residences/businesses along river banks.

According to the USGS, the probability of eruption- generated lahars affecting the Sandy and White River valleys is 1-in-15 to 1-in-30 during the next 30 years, whereas the probability of extensive areas in the Hood River Valley (Portland) being affected by lahars is about ten times less. Pumice is the ash/rock that some volcanos “throw” when they explode. Based on eruptions of Mt. Hood in 1859 and 1865, rocks about 2-3 cm in size are scattered within a 3 mile radius of the summit. Since Portland is about 80 miles away, the chance of sizable pumice hitting the ground is unlikely. However, experiences from the lateral blast of Mt. St. Helens in 1981 show us that ash can travel hundreds of miles. Residents of Portland had sizable quantities of the fine ash deposited on their cars, lawns, and houses after that blast.

Future eruptions of Mount Hood could seriously disrupt transportation (air, river, and highway), some municipal water supplies, and hydroelectric power generation and transmission in northwest Oregon and southwest Washington.


Congrads to PDXJim for FTF (First to Finish logging requirements)


Logging Requirements:

Send the answers to #1-#4 to me through my geocaching profile.

  1. List the name “GC239E9 Mt. Hood View Earthcache” in the first line of your email. Also, list the number of people in your group.
  2. (If you can see the mountain) Contrast the mountain peak shape and size with surrounding hills. Describe two DIFFERENCES and one SIMILARITY.
  3. Based on the information above, what might be the danger(s) to Portland if Mt. Hood should explode?
  4. 11161' is Mt. Hood summit. Based on your altitude at this location, how many vertical feet separate you from the summit?
  5. These are the cords to Mt. Hood’s summit: N45 22.412 W121 41.733. Enter them into your GPS unit. How far away is Mt. Hood from this location? Based on historic effect patterns, what type/size of rocks/flow might affect the spot you are standing on now?
  6. (Per current gc.com guidelines, photos are no longer allowed to be required. HOWEVER they are encouraged, since they can help clarify that you have visited the location if your other logging requirement answers are vague). Post a picture of yourself and/or your GPS with your log that shows Mt. Hood in the background. DO NOT show any of the pertinent information panels in your picture or your log may be deleted.

I will only respond if you have incomplete logging requirements. Go ahead and log your cache


Resources:

USGS – http://vulcan.wr.usgs.gov/Volcanoes/Hood/

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