On May 18, 1980, the town of Othello, Washington was covered with volcanic ash from the Mount St. Helens eruption. Disaster research suggested that a natural disaster acted on impacted populations as a major stressor and could result in such stress-related symtoms/problems as anxiety, depression, alcohol abuse, family problems, etc. It was hypothesized that there would be an increase in the incidence of such symptoms/problems following the ashfall. Most previous research has relied on subjective accounts of victims, but data for this study came from selected objective indices such as mental health caseloads, welfare assistance grants, hospital admissions, police records, etc. Data were compared for a 12-month pre-disaster baseline, and a 7-month post-disaster period. Of the 34 indices examined, five showed significant post-disaster decreases, and nine failed to meet the criterion for significance. Twenty indices showed significant increases and these seemed to clearly support the hypothesis. Two rival hypotheses were explored as possible causal factors: local unemployment rates, and economic factors affecting agriculture. The disaster hypothesis fit the observed data more precisely and seemed most logical as a probably causal agent.

Active seismicity and volcanism north of Washington state’s Mount St. Helens provide key ingredients for hydrothermal circulation at depth. This broad zone of seismicity defines the St. Helens Seismic Zone, which extends well north of the volcanic edifice below where several faults and associated fractures in outcrop record repeated slip, dilation, and alteration indicative of localized fluid flow. Candidate reservoir rocks for a geothermal system include marine metasediments overlain by extrusive volcanics. The colocation of elements comprising a geothermal system at this location is tested here by analysis of the structures potentially hosting a reservoir, their relationship to the modern stress state, and temperature logs to a depth of 250 m. Outcrop mapping and borehole image log analysis down to 244 m document highly fractured volcaniclastic deposits and basalt flows. Intervening ash layers truncate the vertical extent of most structures. However, large strike slip faults with well-developed fault cores and associated high fracture density cross ash layers; vein filling and alternation of the adjacent host rock in these faults suggest they act as vertically extensive flow paths. These faults and associated fractures record repeated slip, dilation, and healing by various dolomite, quartz, and hematite, as well as clay alteration, indicative of long-lived, localized fluid flow. In addition, where these rocks are altered by igneous intrusion, they host high fracture density that facilitated heat transfer evidenced by associated hydrothermal alteration. Breakouts in image logs indicate the azimuth of SHmax in the shear zone is broadly consistent with both the GPS plate convergence velocity field as well as seismically active strike slip faults and strike-slip faults mapped in outcrop and borehole image logs. However, the local orientation of SHmax varies by position relative to the edifice and in some cases with depth along the borehole making a simple regional average SHmax azimuth misleading. Boreholes within the seismic zone display a wider variety of fracture attitudes than those outside the shear zone, potentially promoting permeability. Temperature profiles in these wells all indicate isothermal conditions at average groundwater temperatures, consistent with rapidly flowing water localized within fractures. Together, these results indicate that the area north of Mount Saint Helens generates and maintains porosity and permeability suggesting that conditions necessary for a geothermal system are present, although as yet no modern heat source or hydrothermal circulation was detected at shallow depth. / Geology

The eruption of Mount St. Helens in 1980 severely impacted the woody vegetation within the geomorphic floodplain as well as the morphology of the Upper South Fork Toutle River. Historic aerial imagery and LiDAR data were used in combination to create snapshots of the channel and vegetation in 1980, 1983, 1996, 2003, and 2014. This data was mapped and analyzed using GIS, with the primary focus on 2D channel change, vegetation change, and channel-vegetation interactions from 1980 to 2014. No vegetation was discernable in 1980-83 but the vegetation present in 1996 increased in area and in density from 1996 to 2014. The number of channels locations were dependent on vegetation density and presence while vegetation growth occurred predominately in areas previously occupied by the channel.

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Comprehension of eruptive histories is critical in understanding the evolution of magmatic systems at arc volcanoes and may supply evidence to the petrogenesis of intermediate and evolved magmas. Within the 300 ka eruptive history of Mount St. Helens, Washington, the Kalama Eruptive Period, 1479- ~1750 CE was bracketed by interludes of quiescence (Hoblitt et al., 1980) and thus likely represents an entire eruptive cycle within a span of 300 years. Study of the magmatic evolution during this short time period provides key information regarding inputs and the plumbing system of Mount St. Helens. This research aims to enhance comprehension of processes leading to the petrogenesis of intermediate magmas by providing whole rock and phase geochemical data of an eruptive cycle, thereby providing constraints on the magmatic evolution of the Kalama Eruptive Period. The eruptive sequence is divided into early, middle and late subperiods. The early Kalama began with two dacitic plinian eruptions and continued with smaller eruptions of dacite domes (64.4-66.5 wt% SiO₂) that included quenched mafic inclusions (53.7-57.7 wt% SiO₂). The middle Kalama signified the onset of basaltic andesite and andesite eruptions ranging between 55.5-58.5 wt % SiO₂. Subsequently, summit domes that began as felsic andesite (61-62.5 wt% SiO₂) and transitioned to dacite (62.5-64.6 wt% SiO₂) dominated the late Kalama. Previous work on Kalama-aged rocks suggests magma mixing is an integral process in their production. Compositions and textures of crystal phases, in addition to the presence of xenocrysts in middle and late Kalama rocks, confirm mechanical mixing of magmas likely produced many of the sampled compositions. New petrographic observations were integrated with new whole rock and phase EMP and LA-ICP-MS data and the known stratigraphy in order to constrain the magmatic and crustal components active during the Kalama Eruptive Period. New findings include: 1. Two populations of quenched mafic inclusions, one olivine-rich and one olivine-poor, are identified from the early Kalama based on mineralogy, textures, and major and trace element chemistry. Major element modeling shows crustal anatexis of plutonic inclusions found in early Kalama dacites could produce the felsic magma source of the olivine-poor population. The olivine-rich population incorporated cumulate material. 2. Four distinct lava populations erupted during the early part of the middle Kalama (X lavas), including two found exclusively in lahar deposits: M-type lahars are the most mafic, B-type lahars are more mixed, the Two Finger Flow was previously grouped with other middle Kalama-age lavas, and the X lava (in situ) has unique geochemical and textural character. X tephras likely correlate with the lavas. 3. There were at least three mafic source contributions at Mount St. Helens during the eruptive period: the parent to the X deposits, the cumulate material in the olivine-rich QMIs, and the calc-alkaline parent to the MKLV and SDO. The magma reservoir at Mount St. Helens has been modeled as a single, elongate chamber (Pallister et al., 1992). Multiple coeval basaltic or basaltic andesite parents fluxing into the magmatic system beneath the volcano could indicate a more complex magma chamber structure. / Graduation date: 2011