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Keith A. Howard

Publications and source records attributed to Keith A. Howard.

At least 91 records · Page 5Linked to original sources
USGS1984

Canyon-filling lavas and lava dams on the Boise River, Idaho, and their significance for evaluating downcutting during the last 2 million years

Basalts that periodically dammed the Boise River and its South Fork over the last 2 million years reveal the canyon history and illustrate how lava interacted with impounded river water. Intracanyon basalt flows record a granite canyon successively filled by lava and then recut at least five times in the last 2 million years. The most voluminous flow, Steamboat Rock Basalt, reached 60 kilometers downstream and spread out on the Snake River Plain just east of Boise. Lavas that reached the river were erupted from vents bordering the main canyon and adjacent tributaries. The river canyon was periodically flooded by basalt from these eruptions, reentrenched to a new lower level, then flooded again. This succession resulted in terraces of older flows high above the river and of younger flows lower on the canyon walls. The canyon-filling flows dammed the river and created deltas of pillow basalt and hyaloclastite overlain by massive subaerial basalt. Foreset beds in the hyaloclastite deposits and inclined pillows indicate flow into reservoirs behind the lava dams. A well-documented example of a lava dam is the one formed by the Smith Prairie Basalt, which is about 0.2 million years old. Potassium-argon ages calibrate a canyon history in which the river was lowered at a rate between 0.005 and 0.01 centimeter a year over the last 2 million years. The lava dams interrupted this lowering but were each rapidly incised in about a quarter of a million years at rates averaging 0.03 to 0.07 centimeter a year.

Idaho↗
USGS1983

Introduction

Tectonic and Stratigraphic Studies in the Eastern Great Basin is compiled as a tribute to Max D. Crittenden, Jr., whose geologic leadership and exemplary studies in the eastern Great Basin region have stimulated significant scientific advances. Many of the authors in this volume conducted their studies with assistance from Max, and much of the foundation for these studies is his work on the foreland thrust belt in the Wasatch Mountains of Utah.

GSA Memoirs↗
USGS1983

Correlation of metamorphosed Paleozoic strata of the southeastern Mojave Desert region, California and Arizona

Isolated outcrops of deformed, regionally metamorphosed Paleozoic strata are scattered within the southeastern Mojave Desert region of California and western Arizona. These strata unconformably overlie a basement of Proterozoic crystalline rocks and are overlain in turn by metamorphosed Mesozoic sedimentary rocks. The strata can be correlated lithostratigraphically with the classic cratonal Paleozoic section of the western Grand Canyon, Arizona, and with nonmetamorphosed Paleozoic sections transitional between cratonal and miogeoclinal in the Ship, Marble, and Providence Mountains, California. The strata evidently were once continuous with Paleozoic epicontinental strata exposed throughout the southern Great Basin and Colorado Plateau. Outcrops of Paleozoic strata and of the underlying Proterozoic basement in the southeastern Mojave Desert region define a terrane that has been disrupted by Mesozoic thrust faults and by Tertiary detachment faults but that nevertheless retain a gross paleogeographic coherence. This coherent terrane extends at least as far west and southwest as the Big Maria, Palen, and Calumet Mountains, and possibly beyond to include Paleozoic exposures in the San Bernardino Mountains and near Victorville. Poorly understood tectonic boundaries separate the area of paleogeographic coherence from known or suspected allochthonous terranes in the western Mojave Desert and the eastern Transverse Ranges.

Arizona, California↗
USGS1980

Metamorphic infrastructure in the northern Ruby Mountains, Nevada

The metamorphic complex of the northern Ruby Mountains in northeastern Nevada exposes Paleozoic strata that are metamorphosed to sillimanite grade, migmatized, and recumbently folded. Nappes are variously overturned to the east, north, south, and west. The deeper part of this metamorphic infrastructure is a migmatitic zone pervaded by pegmatitic two-mica granite. A structurally higher transition zone underwent extreme tectonic flattening and some thrusting as the mobile infrastructure rose buoyantly against more rigid suprastructure. Relief by flow and stretching to the west-northwest and east-southeast resulted in a regionally constant lineation in this transition zone. The age of metamorphism is uncertain but may be Jurassic.

Nevada↗
USGS1978

Climate variation and its effects on our land and water : Part C, Geological Survey climate plan

To better coordinate information being generated by the U.S. Geological Survey, a workshop was convened near Denver, Colo., on December 7-9, 1976, to exchange ideas about research that is oriented toward climate, climate variation, and the effects of climate on the Nation 's land and water resources. This is the first circular of a three-part report resulting from that workshop. Hydrologic records provide information to the earth scientist about the responses of ground water, surface water, and glaciers to climatic change; geologic sequences provide evidence of earth-surface water, and glaciers to climatic change; geologic sequences provide evidence of earth-surface responses to climatic change; biological records yield information about the effects of climatic change on the Earth 's biota; archeological records tell us where and how man was able to live under changing climatic conditions; and historical records allow the specific effects of short-term changes in climate to be accurately documented. The interrelation between present and past geologic environments, various methods of study , and the span of time over which the results can be applied are shown in a table. (Woodard-USGS)

Circular↗