Hey Rick, What's it Tuya? EarthCache
Hey Rick, What's it Tuya?
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This Earthcache introduces a very unique geological feature known as a tuya. Oregon has the only two tuyas (yes there are two) in the United states. A tuya is formed beneath a glacier when there are volcanic eruptions that cannot penetrate the ice sheet above creating a flat-topped hill that conforms to the shape of bottom of the ice. The picture below shows two volcanic landforms in the Cascade Mountain Range of Oregon. The tuya is the landform on the right.
Hayrick Butte is a nearly flat triangular plateau about 0.5 miles (0.8 km) across with steep walls rising about 700 feet (210 m) above the plain below.
You can clearly see the table-like shape of Hayrick Butte, contrasted against the cone-shaped Hoodoo Butte. Although probably only a few thousand years separated their formation, their shapes were clearly defined by whether they formed beneath an ice sheet, as Hayrick did, or erupted into the air, as Hoodoo did.
How a Tuya is formed.
At first, the lava erupts in much the same way it does in the deep sea. Ice-contact eruptions can form quite impressive glassy pillows. Part of the lava shatters as it contacts the ice, leaving a kind of hydrated tuff-like breccia called hyaloclastite. It is glassy and lacking the iron oxide crystals that are more common in other types of eruptions.
As the ice above the eruption melts into a lake, the more explosive the interactions of fire and water become. The rock has the appearance of angular flat fragments.
When the lake is filled and/or boiled away, lava flows more gently again, forming thick flows, often with columnar jointing that forms as the rock slowly cools.
Much of the evidence of Hayricks' subglacial origin has been removed by other erosional glacial processes, but there are still places where you can see for yourself that the columnar joints formed by lava meeting ice are still present. The steep sides formed because the lava that had erupted couldn’t flow far due to the ice surrounding it.
Hayrick Butte likely formed during the height of the last ice age during the Pleistocene, while the nearby Hoodoo Butte was not formed subglacially, thus its more typical cone-shaped profile and lightweight, gas filled, iron-rich cinders or scoria. This tuya and its companion Hogg Rock , only 2 miles to the North, are also great evidence that there was once an ice sheet covering the Central Oregon Cascades where today few glaciers remain.
To claim this Earthcache you need to answer the following questions by emailing them to the cache owner. All found it logs not accompanied by the corresponding email will be deleted. No need to wait for a response from the CO's, go ahead and log the find.
1) What evidence of erosion do you see taking place on Hayrick Butte?
2) Nearby Hoodoo Butte is what kind of volcano? There are three common names, one is adequate, bonus points for all three.
3) Describe how the type of rock varies greatly between Hayrick and Hoodoo Buttes and why.
Bonus: Post a picture of yourself or your GPS and Hayrick and/or Hoodoo Buttes in the background. Pictures will vary greatly based on the season.
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