Shastina

 mountain, summit

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Elevation: 12,330 feet (3758 meters)

Shastina stands apart from other cones of Mount Shasta. Whereas, the central vents for most of Mount Shasta's individual cones are so close together that they have been recognized separately only through detailed study, the Shastina cone lies distinctly to the west and is a notable stratocone in itself. If it were by itself anywhere else in the Cascades it would be considered a major volcano. We mapped out the distribution of lava flows from Shastina and found them all to be younger than the 10,000-year-old pumice deposits of the Red Banks eruption. An initial explosion perforated the west flank of the Misery Hill cone and formed the crescent-shaped crater rim. Mapping showed that Shastina grew quickly by successive eruptions of lava from the new vent, burying the west half of the initial crater and forming the Shastina cone. Dating of charcoal from deposits below and above the Shastina lavas indicates that this cone grew within no more than a few centuries.
At the end of Shastina's cone growth, many domes of viscous lava extruded in the summit crater. These extrusions were punctuated by explosive eruptions and collapse of the domes. This activity broke down the western crater rim and spread hot lava fragments over the west flank of Shastina and Mount Shasta below. After each series of explosions, another dome grew in the crater. We estimate that at least 4 or 5 lava extrusions and subsequent explosions occurred at Shastina.
The oldest domes form the north and south crater rims, and remnants of 3 younger domes rise above the crater floor. The broken down west rim of Shastina's crater is the head of Diller Canyon. The explosions in Shastina's crater blasted hot lava fragments into the head of Diller Canyon. The debris spread out in destructive pyroclastic flows–high-speed flows of hot volcanic ash, blocks, and gases–and buired the west flank of Shastina and the lowlands beyond. There are large fractured blocks of lava.
Room-sized blocks were carried in these pyroclastic flows and left behind to litter the surface of the fan of hot debris. Such blocks–one of them contracted upon cooling to form three-dimensional jigsaw puzzles of prismatic fractures perpendicular to each surface of the block.
The last event related to the spectacular volcanism of Shastina was the extrusion of another volcanic dome low on its western flank. This dome rises steeply beside Interstate Highway 5, the main north-south artery of ground travel among the Pacific Coast States. The dome suffered partial collapse by avalanching of hot debris, spreading flows of hot volcanic ash and blocks to the west and south. The town of Weed and part of the town of Mount Shasta are built on the surfaces of the 9,400-year-old ash pyroclastic flows from Shastina and Black Butte.

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