Mount Hood Research Articles

Seismicity of Mount Hood and structure as determined from teleseismic P wave delay studies

A 16‐station seismic network was established in the Mount Hood area of Oregon in 1977 as part of a multidisciplinary study to evaluate the geothermal potential of a typical Cascade volcano. The immediate objective was to monitor local seismicity and to study the P wave velocity structure of the crust and upper mantle. During the 13 months the network was in operation, 10 local earthquakes were recorded. All these events are spatially associated with the volcano and occurred at shallow depths roughly defining a zone striking north‐northwest. The largest earthquake, a magnitude 3.4 event, was preceded by a single foreshock and followed by three locatable aftershocks. These and the five other located earthquakes were of magnitude less than 2.0. Fifty‐five teleseisms were recorded by the network and used in a teleseismic P wave delay study. The residuals from the P delay study indicate that there is no significant velocity anomaly associated with the Mount Hood volcano and only small velocity variations in the Mount Hood region.

Interpretation of shallow electrical features from electromagnetic and magnetotelluric surveys at Mount Hood, Oregon

A magnetotelluric survey, with a reference magnetometer for noise cancellation, was conducted at accessible locations around Mount Hood, Oregon. Thirty‐eight tensor magnetotelluric (MT) and remote telluric stations were set up in clusters around the volcano except for the northwest quadrant, a wilderness area. Because of limited access, station locations were restricted to elevations below 1829 m, or no closer than 5 km from the 3424‐m summit. On the basis of the MT results, three areas were later investigated in more detail using a large‐moment, controlled‐source electromagnetic (EM) system developed at Lawrence Berkeley Laboratory and the University of California at Berkeley. One‐dimensional interpretations of EM and MT data on the northeast flank of the mountain near the Cloud Cap eruptive center and on the south flank near Timberline Lodge show a similar subsurface resistivity pattern: a resistive surface layer 400–700 m thick, underlain by a conductive layer with variable thickness and resistivity of <20 ohm m. It is speculated that the surface layer consists of volcanics partially saturated with cold meteoric water. The underlying conductive zone is presumed to be volcanics saturated with water heated within the region of the central conduit and, possibly, at the Cloud Cap side vent. This hypothesis is supported by the existence of warm springs at the base of the mountain, most notably Swim Warm Springs on the south flank, and by several geothermal test wells, one of which penetrates the conductor south of Timberline Lodge. The MT data typically gave a shallower depth to the conductive zone than did the EM data. This is attributed, in part, to the error inherent in one‐dimensional MT interpretations of geologically or topographically complex areas. On the other hand, MT was better for resolving the thickness of the conductive layer and deeper structure. The MT data show evidence for a moderately conductive north‐south structure on the south flank below the Timberline Lodge and for a broad zone of late Tertiary intrusives concealed on the southeast flank.

A magnetic investigation of Mount Hood, Oregon

Aeromagnetic data over the Mount Hood area of Oregon are dominated by the topographic expression of highly magnetized Cenozoic volcanics. Three‐dimensional magnetic modeling of the Mount Hood volcanic cone indicates that the bulk of the cone, above approximately 1650 m elevation, is composed of magnetically similar andesites. The andesites are magnetized in a normally polarized direction (I = 80.0°, D = 28.3°) and with a magnetization of 2.9 A/m. The chief exception to this is the possible remains of an old cone which underlies the northwest slope of the Mount Hood cone. Calculations show that this old cone is magnetized with a direction approximately opposite to the earth's present field and with a magnitude of magnetization of 3.9 A/m.

Upper crustal structure of the Mount Hood, Oregon, region as revealed by time term analysis

Seismic refraction data with a dense areal distribution were collected to study the seismic structure of Mount Hood and the surrounding region. This area is typical of Cascade volcanoes and is geologically quite complex. The prime goals of this project were to search for velocity variations in the upper crustal rocks and to determine if the velocity of these rocks is anisotropic. A new system, including 100 remote recording units, was developed to facilitate the collection of data in this type of survey. The data collected in this study reveal a large variation in velocity and thickness of the uppermost crustal rocks that is probably typical of the High Cascade province. A regional structural pattern surrounding Mount Hood, where there is a marked thinning of low‐velocity near‐surface rocks, suggests that the present edifice of Mount Hood lies on top of a much larger structure, possibly the roof of a large batholith that was emplaced prior to the eruption of the volcanic rocks that form the modern mountain. A straightforward time term analysis of the data reveals this structure. When the time terms are used to correct the travel time observations for the variation in structure under each station, the remaining set of residuals indicates a variation of travel time with azimuth. While a systematic error in the time term reduction cannot be ruled out, this variation is probably the result of anisotropic velocity structure in the underlying refractor. The alignment of the direction of maximum velocity with the direction of maximum principal stress and the decrease in anisotropy with depth suggest that the anisotropic velocity structure is related to the opening and closing of fractures in the present stress field. The direction of maximum velocity is about N25°W, and the degree of anisotropy appears to vary with depth from about 3% near the surface to zero at depths below 8 km.

Oil and Gas Developments in West Coast Area in 1981

The total exploratory footage and number of wells drilled in the onshore area of California during 1981 increased approximately 10% and 20%, respectively, over the 1980 figures. Both the average footage drilled per well (5,579 ft) and the percentage of success (32.7%) showed declines from 1980. Eight wildcats established new fields in 1981. Two of the wildcats discovered new oil fields and 6 found new gas fields. An additional gas find has been treated as a discovery because of its stratigraphic significance. Onshore development drilling included 2,078 wells; 97% of these were completed as successful producers, the same percentage as in 1980. For the California offshore, just 5 exploratory well completions were reported to the Committee on Statistics of Drilling in 1981; only 2 were successful. Texaco announced its Pitas Point gas field extension in May, and Chevron announced a new oil field discovery, the Point Arguello, in October. There were 118 development wells drilled, of which 99 (83.9%) were successful. Development footage and number of wells were up, but the percentage of success declined from 90% in 1980. California's oil production reached an all-time high of 384.8 million bbl in 1981. The state's previous record, set in 1968, was 375.4 million bbl. Geothermal activity in California centered on development of the proven Imperial Valley and Geysers areas and the discovery of the Coso area in Inyo County. Activity in Oregon included evaluation of the Mount Hood and Newberry Volcano areas. Oil and gas exploratory drilling in Oregon during 1981 led to the discovery of a new gas field by American Quasar in Linn County and to the establishment of a new gas pool by Reichhold Energy at the Mist field in Columbia County. The major portion of Washington's exploratory drilling in 1981 was carried out by Shell in Kittitas County in the south-central part of the state. At last report, the hydrocarbon accumulations found had been deemed noncommercial.

Environmental Analysis: A Ranger District's Approach to NEPA

Abstract Two timesaving refinements to the USDA Forest Service's basic NEPA guidelines have been developed by staff of the Bear Springs Ranger District, Mount Hood National Forest, Oregon. The staff's approach to environmental evaluation combines a formal decision-making process and a threshold-of-concern technique to formulate and analyze management alternatives.

Leucoplasts Mimicking Membranous Chromoplasts

Summary Leucoplasts of coronae of a variety of the daffodil ( Narcissus pseudonarcissus L.) with white flowers (cv. «Mount Hood») exhibit the same fine structural appearance as membranous chromoplasts of the wild type. Their concentric internal membranes are — except for the absence of carotenoids — virtually identical with chromoplast internal membranes with respect to both protein and lipid composition. Consequently, the carotenoids cannot be regarded as being essential for the molecular build-up of these membranes.

Volcanic energy studied at Mount Hood

Geochemical and geophysical measurements at Mount Hood are being made by a team of scientists from various institutions for the Department of Energy. Norman Goldstein of the University of California's Lawrence Berkeley Laboratory explains that locating sources and track pathways of hot water circulating within the volcano may help engineers use the geothermal potential of Mount Hood. Hot geothermal waters could help heat nearby ski lodges in the Mount Hood resort area, and if higher temperatures are available, they could operate steam‐driven turbines to generate electricity for the nearby city of Portland.

Palaeomagnetic record of a late Tertiary field reversal

summary. A palaeomagnetic record of a field reversal has been obtained from the Tatoosh intrusion in Mount Rainier National Park (latitude 46° 50° N, longitude 121° 45′W). fie VGP before and after the reversal is conformable with the North American polar wander curve. The reversal in direction is preceded by a decrease in intensity of the NRM of more than an order of magnitude. Immediately prior to the reversal the dispersion of the directions of magnetization increases. The reversal in direction is accomplished by a convoluted VGP path which traverses the Pacific and is somewhat confined in longitude. Subsequent to the completion of the change in direction the field intensity recovers, so that the intensity change takes at least twice as long as the directional change. The definition of the reversal plane in the Tatoosh intrusion gives the orientation of the cooling front at the time the reversal took place. An analysis of the cooling history of the body, in conjunction with the magnetic results, suggests that the body did not cool by simple conduction, and that convective heat transfer by meteoric water is important. This defines a two-stage cooling of the margin. At high temperature rapid cooling takes place as the water chills the hot rock. Later the circulating water in the cracked permeable margin maintains a moderate temperature for long periods. Long vertical cores from the intrusion have revealed a palaeomagnetic record similar to present secular variation records and suggests that some tens of metres of core from intrusive similar to the Tatoosh could give important resolution records of the geomagnetic field. A second reversal record was obtained from the Laurel Hill intrusion near Mount Hood, Oregon (latitude 45° 20′N, longitude 121° 4′W) which is approximately 10 Myr younger. The smoothed VGP paths for the two reversals are essentially identical. Other RN paths from North America appear to favour the Pacific, although the Lake Tecopa record of the last reversal is a notable exception. In comparing all available reversal paths, one finds that although individual paths are confined in longitude, no longitude is uniquely preferred nor does the site uniquely determine a path longitude. There is some preference amongst RN paths to favour the Pacific and the NR the Euroasian landmass, but the limited distribution of observation sites precludes a satisfactory distinction between site control or absolute control in geographical coordinates. Dominantly quadrupolar transitional fields are consistent with the records. Such fields are predicted by a variant of the Steenbeck Krause α2 DC dynamo, but αω dynamos may also exhibit quadrupolar transitional fields as indeed does the Sun. Some stationary nonaxisymmetric component is required to explain non-zero declination of the observed transitional fields.

Goal Programing in Land-Use Planning

Abstract The land-use planning process on the Mount Hood National Forest involves nine steps designed to identify needs, determine the complex interaction of effects from fulfilling these needs, and providing a means by which decisionmakers can see the tradeoffs required to achieve the various levels of need satisfaction. Goal programming, a variation of linear programming, has been experimentally used to assist in this process.

Crystallization and Fractionation Trends in the System Andesite-H2O-CO2-O2 at Pressures to 10 Kb

Phase relations of a Mount Hood andesite, which has the composition of an average orogenic andesite, have been determined as a function of O 2 fugacity at 1 atm and of H 2 O fugacity to pressures of 10 kb, at O 2 fugacities of the quartz-fayalite-magnetite (QFM) buffer. All runs contained either a H 2 O or H 2 O–CO 2 fluid phase; melts in runs with a H 2 O–CO 2 fluid phase were H 2 O undersaturated. The H 2 O contents of the melts and H 2 O fugacities were calculated from NaAlSi 3 O 8 –H 2 O thermo-dynamic data on the assumption of ideal mixing in the system H 2 O–CO 2 . One-atmosphere runs show that melting relations of silicates are little affected by f o 2 but that both ilmenite- and magnetite-out temperatures are raised by higher f o 2 . Ilmenite precipitates at higher temperature than magnetite. In these runs and in all runs at high pressure with H 2 O and H 2 O–CO 2 fluid phases, oxides were not stable at temperatures of the silicate liquidus. Oxides might be stable on the silicate liquidus if f o 2 rose two or more log units above the Ni–NiO (NNO) buffer. However, calculations indicate that in natural magmas, those processes which might change f o 2 —crystal-liquid equilibria or exchange of H 2 , or H 2 and H 2 O with the wall rocks—cannot raise f o 2 by that magnitude. Because differentiation of basalt melts to andesite must involve iron-rich oxide phase subtraction, such fractionation models appear unreasonable. For the Mount Hood andesite composition, plagioclase is the liquidus phase under H 2 O–saturated conditions to 5 kb and under H 2 O–undersaturated conditions at 10 kb when the H 2 O content of the melt is less than 4.7 wt percent. For higher H 2 O contents, either orthopyroxene or, at H 2 O saturation at pressure greater than 8 kb, amphibole assumes the liquidus. In all cases, clinopyroxene crystallizes at lower temperature than orthopyroxene. Melting curves in the H 2 O–under-saturated region may be contoured either as percent H 2 O in melt or as P e H 2 O ; in either case, the topology of the various silicate melting curves is different from the case of H 2 O–saturated melting. Therefore, melting relations determined at H 2 O–saturated conditions cannot be used successfully to predict melting relations in the H 2 O–undersaturated region. Amphibole melting relations were studied isobarically at 5 kb as a function of temperature and fluid-phase composition. Amphibole has a maximum stability temperature of 940 ± 15°C for fluid compositions of 100 to 44 mole percent H 2 O; for fluids containing more CO 2 than 56 percent (or, equivalently, less than 4.4 wt percent H 2 O in melt), the melting temperature is lower. The same relations would be seen if CO 2 were not present and the melt were H 2 O undersaturated. These rather low melting temperatures, relative to other silicate phases, preclude andesite generation by basalt fractionation involving amphibole at pressures less than 10 kb.

Changing the Fire Detection System on the Mount Hood National Forest

Changing the Fire Detection System on the Mount Hood National Forest

Studies in North American Bryaceae I-II

Studies in North American Bryaceae I-II

Additions and Revisions to the Genera of North American Caddisflies of the Family Brachycentridae With Special Reference to the Larval Stages (Trichoptera)

AbstractLarval characterizations for the genera of North American Brachycentridae are revised and two new genera created, bringing to five the total number now recognized on this continent. Previous concepts of larval morphology inMicrasemaare emended. Discovery of the larval stage ofBrachycentrus(Amiocentrus)aspilusRoss necessitates elevation of this subgenus to generic status. Association of larvae with the two North American species placed inOligoplectrumnecessitates removal of one,O.dimicki(Milne), toMicrasema. Discovery of all stages of a new species on Mount Hood, Oregon, necessitates creation of a new genus. A provisional larval key to the genera of the North American Brachycentridae is proposed and the phylogenetic relationships of the genera are discussed. Validity of the Asian genusOligoplectrodesis questioned.

Color film on snow‐surveying in the Central Sierra Nevada

This color‐film was thoroughly enjoyed by all present as at Seattle. It has now been expanded by the addition—made possible by the trip to the Pacific Northwest last summer—of a film on Crater Lake, Mount Hood, Mount Baker, and the Washington‐Oregon ocean surf.

The Stevens seasonal snow‐rain recorder

(At the second Western Interstate Snow‐Survey Conference in 1934 [Trans. Amer. Geophys. Union, 15th Annual Meeting, pp. 632–633, 1934], a brief note was presented of the Stevens snow‐and‐rain recorder. The actual recording of winter precipitation on Mount Hood for the month January 14 to February 13, 1938, is sufficiently promising to merit further notice at this time, although the record was made after the close of the Davis Conference.)Long‐time records of cumulative precipitation in any form—snow, rain, sleet—are obtainable with this recorder. From the graph of cumulative precipitation the intensity for any period is readily determined.

The Naming of Mount Hood

The Naming of Mount Hood

The Volcanic Activity of Mount St. Helens and Mount Hood in Historical Time

The Volcanic Activity of Mount St. Helens and Mount Hood in Historical Time

CAUSE OF “SMOKE” FROM MOUNT HOOD

CAUSE OF “SMOKE” FROM MOUNT HOOD

“OUT OF THE WORLD”

IT is indeed pleasant to be remembered when one has been out of the world for so many months. Out of the world? you might ask. Why? Are you not in that great northwest where fruit grows, with irrigation, so large that but one apple is needed to make a pie, one turnip suffices for a family, and potatoes weigh three pounds each ? where oats, clover, and alfalfa are cut three times a year, yielding large crops at each cutting? Yes, in various parts these things are all true. Yet, ninety-five miles from a railroad! Not a two hours' ride in a private conveyance, but forty miles by coach and four, and forty-five miles by automobile, taking, the shortest time, twelve hours; and when the auto breaks-some hours more for repairs. Would you care to take the trip with me? Come, don your heaviest winter clothes, not your medium weight, and we will start at seven in the morning. Over a vast plateau we go, enormous sheep ranches, said by some to be the largest in the world, to us seeming to be boundless desert. But as we keep on the lookout for something of interest, we see Mount Hood appear on the horizon. Ah, it disappears as we begin the descent into Cow Canyon. Down, down we go,-surely we will tip over for the winding road is narrow. Is it possible to make that turn? are we to go into that rock? No, the coachman, slow though his horses are, so is he sure. To the very bottom we wend our way, then through the canyon. As we near Madras, ranches are seen where wheat is easily grown, for large fields spread on either side. At this little town we dine at one-thirty, then take the automobile and go on our way rejoicing. The country around us is covered sparsely with sage brush and juniper trees, the latter of which, by the way, began to grow some two thousand years ago, we are told. The lava dust is thick and on our right see the vast pile of lava rock, layer on layer. Where does that come from? you ask. It is the supposition of a friend, a student of geology, that this entire region was at one time covered with hot springs, for white ashes or cinter 318