Day #30 Outcrop: Hyaloclastite Boulder

Close by the base of a series of Recent rhyolitic lava domes near South Sister Volcano in the central Oregon Cascades is an outcrop of hyaloclastite. You can make out a number of large glassy clasts in an altered palagonitic matrix, presumably the result of either a sub-lacustrine or subglacial eruption in the area.

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Hyaloclastite Boulder, central Oregon Cascades
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