DESCRIPTION:
Pelican Butte, Oregon

[Map,20K,InlineGIF]
Map, Major Volcanoes of the Southern Oregon Cascades

Pelican Butte is a normally polarized, steep-sided andesite shield built on faulted Pliocene and early Pleistocene basaltic andesite. Pleistocene glaciation carved a steep canyon and broad cirque in the northeast flank of the volcano, lowered the summit some tens of meters, and exposed a lava-filled intrusive conduit. However, the volcano's original shape is largely preserved. Pelican Butte (20 cubic kilometers) is volumetrically one of the larger Quaternary volcanoes between Crater Lake and Mount Shasta; it is larger by one-third than the nearby more scenic Mount McLoughlin. Two analyzed samples contain 58 and 60 percent SiO2.

Two types of andesite make up most of the volcano. Thick platy flows are most common low on the mountain. These glassy flows traveled far down the slopes of Pelican Butte following preexisting channels. Phenocryst minerals are plagioclase, augite, hypersthene, and locally olivine; all are inconspicuous and collectively make up no more than a few percent of the lava.

The second type of andesite forms thin flows that have scoriaceous and blocky tops. Lava of this type is common near the summit of Pelican Butte. It is typically fine-grained and vesicular. Small snow-white plagioclase phenocrysts of sodic labradorite are characteristic. ...

Pelican Butte's summit is high, the mountain is detached from the axis of the Cascades, and it formed on top of a system of down-to-the-east normal faults with large displacements that delineate the east side of the Cascade Range at this latitude. For these reasons, views from its summit are impressive. It offers a 180 degree panorama of Cascade Peaks from just south of Crater Lake past Mount McLoughlin and onto the volcanoes in the Mountain Lakes Wilderness. ...

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