The Misery Hill Cone of Mount Shasta

Rapid growth of new cone partly buries Sargents Ridge cone

Photograph by R. Christiansen on 3 July 1975

Much of the bulk of Mount Shasta as we now see it is formed by the Misery Hill cone, whose profile fills this aerial view toward the northeast. Sometime between about 30,000 and 50,000 years ago, a new vent opened on the north side of the old Sargents Ridge cone and erupted layers and materials that partly buried it. We found little evidence of erosion between the layers of the Misery Hill cone, showing us that the cone-building eruptions occurred rapidly, perhaps within a few thousand years.

Pace of eruptive activity declines, erosion takes over

Photograph by R. Christiansen on 16 July 1975

After a short period of rapid cone growth, a much longer period of glacial and stream erosion followed, although a few eruptions still occurred on the volcano. In this view up Ash Creek on the east side of Mount Shasta we see the trace of an old drainage on the flank of the Misery Hill cone. A lava flow that came down that old valley from a summit vent partly filled the valley and preserved its ancient profile. Re-excavation of the valley by modern Ash Creek has exposed the flow in cross section, forming the cliff over which Ash Creek Falls tumbles (click image for a larger-sized image). Cooling of the hot lava against the old valley walls caused it to contract and fracture perpendicular to the ground. Where we see them today, these fractures form the sides of "columns" along the base of the flow.

Lava dome fills summit crater
Photograph by R. Christiansen on 24 July 1975	The last volcanic event that added new material to the Misery Hill cone was a lava dome at its summit. In the aerial view on top left, looking toward the northeast, part of an eroded crater rim of the Misery Hill cone forms a horizontal ridge. The dome filled most of this crater and makes Misery Hill itself. The summit of Mount Shasta is the youngest cone of Mount Shasta, known as the Hotlum cone. See description of Red Banks below. In the image at lower left, a geologist stops to ponder the name Misery Hill—it was given by climbers who commonly ascend Mount Shasta from the southwest and struggle up a steep rubble-covered slope. Most climbers think they are on the last leg to the top when they ascend the crest. The true summit still rises more than 300 m above them.
Photograph by C. D. Miller

Explosive eruptions generate pyroclastic flows

Photograph by R. Christiansen on 29 July 1975

The extrusion of hot volcanic domes at the summit and on the flanks of the Misery Hill cone was punctuated by partial disruption of those domes through collapse or volcanic explosion. Fragments would then tumble down the volcanic slopes as hot pyroclastic flows of ash, lava fragments, and gas spread out onto the debris apron below. Here, in the walls of a canyon carved by Mud Creek into the lower flank of the Misery Hill cone, we see deposits left by such pyroclastic flows as successive layers. The layers consist of both coarse blocks and fine volcanic ash. They are generally gray in color, which is the color of the original rock debris, but we commonly find the top of each individual layer to be pinkish, where iron in the hot material oxidized as it cooled in contact with the air. Our studies of these deposits, layer after layer, make us aware that explosive eruptions and pyroclastic flows can reach anywhere on the volcano and sweep over the slopes far below.

Explosive eruption forms Red Banks pumice layer
Photograph by C.D. Miller	The last eruption from the old Misery Hill summit vent explosively ejected pumice and ash, much of which fell back onto all slopes of the volcano. Part of the deposit is preserved as the prominent Red Banks, seen just below Misery Hill dome (see image above). In this view at upper left, we see the Red Banks deposit to be at least partly consolidated and forming a low cliff. This consolidation probably reflects the action of hot gases that escaped from the deposit as it cooled, oxidizing iron in the glassy pumice to produce its orange-red color and slightly sintering the fragments together. Pumiceous deposits from this eruption are found on all sides of the volcano, emplaced both as hot pyroclastic flows and fall deposits from an eruption column of volcanic ash and pumice. The deposits are especially thick northeast of Mount Shasta, the dominant downwind direction. Pumice of the Red Banks eruption is easily identified, and we use it as a marker of stratigraphic position in other deposits. In the lower left image, the Red Banks pumice appears above the contact where the geologist is examining the streambank along Mud Creek. Charcoal collected from the Red Banks deposit gives a date of about 10,000 years for the eruption.
Photograph by R. Christiansen on 29 July 1977

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References