Volcanology Commons^™

Taylor Instability In Ryholite Lava Flows, B. A. Baum, W. B. Krantz, Jonathan H. Fink, R. E. Dickinson

Geology Faculty Publications and Presentations

A refined Taylor instability model is developed to describe the surface morphology of rhyolite lava flows. The effect of the downslope flow of the lava on the structures resulting from the Taylor instability mechanism is considered. Squire's (1933) transformation is developed for this flow in order to extend the results to three-dimensional modes. This permits assessing why ridges thought to arise from the Taylor instability mechanism are preferentially oriented transverse to the direction of lava flow. Measured diapir and ridge spacings for the Little and Big Glass Mountain rhyolite flows in northern California are used in conjunction with the model …

The Mechanism Of Intrusion Of The Inyo Dike, Long Valley Caldera, California, Ze'ev Reches, Jonathan H. Fink

Geology Faculty Publications and Presentations

We analyze the intrusion of the 11-km-long lnyo Dike at the margins of Long Valley caldera, eastern California. The dike trends N07°W and is divided into at least three segments which are rotated by as much as 25° with respect to the main trend. The dike seems affected primarily by the regional stress field of right-lateral shear of the western United States and by the local thermal conditions of the crust; the dike seems unaffected by the preexisting caldera margins and Sierra-Nevada frontal fault system. The high heat flow in Long Valley caldera implies that crustal rocks below 3-4.5 km …

Explosion Structures In Grande Ronde Basalt Of The Columbia River Basalt Group, Near Troy, Oregon, Leonard Lee Orzol

Dissertations and Theses

Explosion structures occur in flows of Grande Ronde Basalt in the study area near Troy, Oregon. Data from nineteen stratigraphic sites indicate that the maximum number of flows that contain explosion structures at any one site is six. In the informally named Troy flow, explosion structures are widespread.

Each flow that contains explosion structures can be divided into two cooling units. The first cooling units occupy troughs in the pre-eruption topography and are up to 10 meters thick. The second cooling units contain the explosion structures and are up to 100 meters thick. The thickness of flows that contain explosion …

Petrology Of The Kula Volcanic Field, Western Turkey, Julie M. Dyer

Geology Theses and Dissertations

The Kula volcanics are a small Pleistocene to Recent volcanic field located on the north shoulder of the Gediz graben, approximately 120 km east of Izmir. The field consists of a mixture of flows, small cones and pyroclastic deposits erupted during three periods of volcanic activity beginning about one million years ago. The volcanics range in composition from basanites to trachybasalts, commonly porphyritic with abundant clinopyroxene, olivine and amphibole phenocrysts. The lavas also host a wide variety of megacrysts, crustal xenoliths and hydrous mantle-derived nodules. These volcanics unconformably overlie Neogene lacustrine sedimentary rocks and the metamorphic basement rocks of the …

Identification Of Endmembers For Magma Mixing In Little Sitkin Volcano, Alaska, Douglas A. Wolf

Geology Theses and Dissertations

Little Sitkin island is an Aleutian calc-alkalic volcanic center that has erupted a suite of lavas ranging from andesite through rhyodacite. Whole-rock chemistry of these lavas indicates contrasting evolutionary processes; major-oxide silica variation diagrams exhibit linear trends that are suggestive of magma-mixing while trace-element trends are largely controlled by accessory-phase fractionation.
Plagioclase, the dominant phenocryst phase in all lavas, commonly occurs in two distinct populations with markedly different compositions and textures. Both normal and reverse zonation is noted in the plagioclase and clinopyroxene of several samples. In addition, clinopyroxene is found as rims on orthopyroxene grains and as cores with …

Fracture Detection In A Volcanic Oil Reservoir Using Discriminant Analysis Of Well Log Data, Joseph William Cross

OES Theses and Dissertations

A new method of detecting fractures using well logs is presented. The technique uses discriminant analysis to distinguish fractured from unfractured reservoir rock and was developed for the volcanic pay zone of Jatibarang oilfield, West Java, Indonesia.

The a priori information required to derive the discriminant function was provided by 22 wells known to penetrate intervals of either fractured or unfractured volcanics. The samples consisted of these 22 intervals digitized in one-meter increments (1256 meters total thickness). The discriminating variables were the petrophysical measurements made by 10 different types of well logs.

Discriminant analysis correctly classified 94.2% of the total …

Tephrostratigraphy Of The Middle Eocene Chumstick Formation, Cascade Range, Douglas County, Washington, Matthew John Mcclincy

Dissertations and Theses

This study outlines the ash (tuff) bed stratigraphy (tephrostratigraphy) in the middle Eocene Chumstick Formation of central Washington. The tuff beds provide local marker beds enabling interpretation of the stratigraphy and structure of the formation. The chemical signature of these units provides the basis on which the units can be traced over broad areas in the basin of deposition. Correlations of tuff beds were obtained over distances of 41 km.

The tephrostratigraphy of the Chumstick Formation consists of nineteen tuff marker beds. Seventeen of these units are chemically characterized in this study. Ten elements were used to fingerprint these tuff …

Tiltmeter Analysis Of Mount St. Helens, Skamania County, Washington, Edward Charles Brown

Dissertations and Theses

Mount St. Helens returned to an active eruptive state March 20, 1980. Since then explosive and dome building eruptions have caused major topographic changes to the mountain and surrounding drainages. Monitoring of the southern side of the mountain by six tiltmeters at distances between 6 km and 12 km was conducted during the period of July 1, 1980 to December 31, 1980. Records obtained from the tiltmeters were analyzed and compared to data from precision geodetic surveys.

Igneous Dikes At Long Valley, Ca: Emplacement Mechanisms And Associated Geologic Structures, David D. Pollard, Jonathan H. Fink, Paul T. Delaney

Geology Faculty Publications and Presentations

Two hypotheses for dike emplacement are: (1) magma flows into and dilates pre-existing fractures; or (2) magma flows into and dilates self-generated fractures. In the first case dikes should be parallel to an element of the rock fabric; in the second, they should be perpendicular to the least compressive stress. The two hypotheses suggest different dike intrusion and fissure eruption mechanisms and therefore different strategies for monitoring igneous events at Long Valley. We derive a method to distinguish the two mechanisms, a priori, from in-situ stress measurements and estimates of magma pressure. Estimates of relative dilation and slip across a …

Quaternary Volcanology Of The West Crater-Soda Peaks Area, Southern Washington Cascade Range, David R. Polivka

Dissertations and Theses

The West Crater-Soda Peaks area covering about 100 km is located 35 km southeast of Mount St. Helens in southern Washington State. It is one of several Quaternary monogenetic High Cascade volcanic centers overlying the Ohaaapecosh Formation of the Western Cascade Group and interstratified glacial till.These volcanic centers are the most westerly of the range.

Geology And Hydrothermal Alteration, Glass Buttes, Southeast Oregon, Dulcy Annette Berri

Dissertations and Theses

The Glass Buttes volcanic complex consists of many domes and individual vents that erupted both rhyolitic and basaltic lavas during the late Miocene to early Pliocene. The east half of the complex, in the vicinity of Little Glass Butte, contains interfingering, finely flow-banded rhyolite and black obsidian flows. The youngest unit, an obsidian, has been dated at 4.9 m.y. East of Little Glass Butte lie two northwest-trending ridges, Antelope and Cascade Ridges, composed of two or more overlapping exogenous domes that formed along northwest-trending faults.

Geology Of A Volcanic Complex On The South Flank Of Mount Jefferson, Oregon, Brian Lee Gannon

Dissertations and Theses

The volcanic stratigraphy and petrography is described for a 46 km² area on the southern flank of Mount Jefferson in the north-central part of the Oregon High Cascades. Here, volcanic processes have been active throughout Quaternary time, resulting in complex stratigraphic relationships. In addition, three formerly recognized glaciations and a two-phase period of neoglaciation have eroded the terrain, depositing tills in contact or interstratified with the volcanic units. Collectively, these processes and the resulting deposits are characteristic of High Cascades development.

Rheological Properties Of Mudflows Associated With The May 1980 Eruptions Of Mount St. Helens Volcano, Washington, Jonathan H. Fink, Michael C. Malin, Richard E. D'Alli, Ronald Greeley

Geology Faculty Publications and Presentations

Rheological properties of three recent mudflows at Mount St. Helens were estimated using techniques developed for determining the properties of debris flows based on the geometry of their deposits. Calculated yield strengths of 1100, 1000, and 400 Pa, maximum flow velocities of 10 to 31 m/s, volumetric flow rates of 300 to 3400 m³/s, and plastic viscosities of 20 to 320 Pa-s all compare favorably with measured and estimated values cited in the literature. A method for determining likely sites of future mudflow initiation based on these data is outlined.

Emission Rates Of Co2 From Plume Measurements., D. M. Harris, M. Sato, T. J. Casadevall, William I. Rose, T. J. Bornhorst

Michigan Tech Publications, Part 1

Most of the CO2 that emanated from Mount St. Helens became part of the gas plume as it moved away from the volcano. An airborne technique was developed for continuous sampling and infrared analysis for CO2 in the plume. The CO2-emission rates were determined by measuring the area, the horizontal velocity, and the CO2 concentration anomaly in vertical cross sections of the plume The emission rate varied from 2100 t/day to about 22 000 t/day.-from Author

Radar Observations Of Ash Eruptions, D. M. Harris, William I. Rose, R. Roe, M. R. Thompson

Michigan Tech Publications, Part 1

Radar systems located at Portland, Oreg., Seattle, Wash., and near Spokane, Wash., have been used extensively for observations of ash clouds from explosive volcanic eruptions at Mount St. Helens during 1980. Eruption clouds are composed of silicate particles and are therefore detectable by radar. Radar observations can be made at night and in overcast weather when conventional observations of eruptions are difficult.-from Authors

Tourmaline - A Prospecting Guide For Massive Base-Metal Sulfide Deposits In The Penobscot Bay Area, Maine, John F. Slack

Maine Collection

Tourmaline - A Prospecting Guide for Massive Base-Metal Sulfide Deposits in the Penobscot Bay Area, Maine

by John F. Slack, U.S. Geological Survey

Special Economic Studies Series No.8

Maine Geological Survey, Department of Conservation, Augusta, Maine (June, 1980).

Contents: Abstract / Introduction / Geologic Setting / Massive Sulfide Deposits / Tourmaline Occurrences / Tourmaline: A Guide to Ore / Acknowledgements / References Cited

Geology Of The Southcentral Margin Of The Tillamook Highlands; Southwest Quarter Of The Enright Quadrangle, Tillamook County, Oregon, Kenneth Allan Cameron

Dissertations and Theses

The Tillamook Highlands is a largely unmapped volcanic pile located in the north end of the Coast Range of Oregon. The 36 square miles of T. 1 N., R. 8 W., on the southcentral margin of the Highlands, was chosen for detailed study.

The study area is composed of Eocene age sedimentary and volcanic units which were deposited in a filling basin. The lowest units were deposited in moderate to deep marine waters; the uppermost were deposited subaerially.

Geology Of The Lewisporte/Loon Bay Area, Newfoundland, Canada, Richard F. Livaccari

Geology Theses and Dissertations

The Lewisporte/Loon Bay area is located within the Central Volcanic belt of Newfoundland. It contains rocks of (?)upper Cambrian to Ordovician in age. The most important group of rocks within this area is the three part Campbellton sequence. The oldest unit of the Campbellton sequence is the Loon Harbour Formation (500-1,000 m thick) composed of mafic volcaniclastics that is conformably overlain by manganiferous cherts of the Luscombe Formation. The Luscombe Formation (370 m thick) is composed of manganiferous cherts that grade upward into highly argillaceous chert. Conformably overlying the Luscombe Formation is the Riding Island greywacke that represents the uppermost …

Petrology And Mineral Chemistry Of Some Jan Mayen Volcanics, Carla A. White

Geology Theses and Dissertations

The island of Jan Mayen is the northernmost active volcano on the Mid-Atlantic Ridge. The rocks of Jan Mayen belong to the potassic series of the alkaline rocks and appear to belong to the straddle type association. The ankaramites and alkali olivine basalts are characterized by the presence of large xenocrysts of rimmed chromium diopside, titaniferous salite, olivine (Fo83 to Fo88), magnetite and sometimes plagioclase (bytownite rimmed by labradorite). Phenocrysts of olivine (Fo74) and plagioclase (andesine) are present in several rocks. These and phenocrysts lie in a matrix composed of` titaniferous salite, olivine (Fo58), plagioclase (andesine), magnetite, biotite and sometimes …

Geology Of The Breitenbush Hot Springs Area, Cascade Range, Oregon, Clifford Michael Clayton

Dissertations and Theses

The Breitenbush Hot Springs area lies on the boundary of folded middle to late Tertiary Western Cascade rocks and younger High Cascade rocks. Within the mapped area the Western Cascade rocks are represented by four formations. The Detroit Beds, a sequence of interstratified tuffaceous sandstone, mudflow breccia, and tuff, is overlain unconformably by the Breitenbush Tuff. The Breitenbush Tuff consists of three units of welded pumice-rich crystal-vitric ash-flow tuffs interbedded with tuffaceous sedimentary rocks. The Outerson Formation unconformably overlies the Breitenbush Tuff and consists primarily of basaltic lava and breccia.

The Outerson Formation includes three localized members: a basal, glassy, …

Petrography, Metamorphism, And Geochemistry Of The Bermeja Complex And Related Rocks In Southwestern Puerto Rico And Their Significance In The Evolution Of The Eastern Greater Antillian Island Arc, Victor J.B. Lee

Geology Theses and Dissertations

Chapter I. Introduction and previous work 1
Chapter II. Geological setting and the petrography of the igneous and metamorphic rocks from southwestern Puerto Rico 6
Chapter III. Metamorphism in southwestern Puerto Rico and relations to the Eastern Greater Antilles 46
Chapter IV. Geochemistry of the Bermeja complex 84
Chapter V. Secular compositional changes of the volcanic rocks in Puerto Rico and other islands in eastern West Indies and the significances of the Bermeja complex 179
Appendix A-E: Petrographic data of the analyzed samples of the Bermeja complex 222
References cited 231

Little Drum Mountains, An Early Tertiary Shoshonitic Volcanic Center In Millard County, Utah, Stephen H. Leedom

Theses and Dissertations

The Little Drum Mountains represent a deeply eroded Eocene-Oligocene volcano, consisting of a vent complex which erupted mafic flows and flow breccias, accompanied by lahars. Flows are dominated by members of the shoshonite suite and contain up to 3.95 percent K₂O, mainly occult in K-rich glass, with K₂O/Na₂O ratios greater than 1.0. In a few interbedded flows, apparently of the calc-alkaline series, pyroxene with varying amounts of plagioclase in a fine-grained groundmass of plagioclase, mafic minerals, and interstitial glass. An ash-flow tuff of the Oligocene Needles Range Formation unconformably overlies the volcanic sequence. Contemporaneous …

Some Ore Deposits In Maine And The Milan Mine, New Hampshire, William H. Emmons

Maine Collection

Some Ore Deposits in Maine and The Milan Mine, New Hampshire

by William H. Emmons

Department of the Interior, United States Geological Survey - Bulletin 432

Washington, D.C. (1910).

Contents: Introduction / Geology / Ore Deposits / Descriptions of Mines / Mines of Hancock County / Mines of Washington County / Mines in Somerset and Oxford Counties / Milan Mine, New Hampshire / Index