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Geology topics

James G. Moore

Publications and source records attributed to James G. Moore.

At least 37 records · Page 2Linked to original sources
USGS2009

Structure and eruptive mechanisms at Surtsey Volcano, Iceland

Glassy basalt tuff was the primary material cored in 1979 from a 181 m deep drill hole on the east tuff ring of Surtsey volcano. Despite the fact that the hole extends 122 m below sea level all the core is similar to the exposed tephra composing the two tuff rings of the island. The tuff includes abundant accretionary lapilli and tuff vesicles, indicating that it was all deposited subaerially. During the growth of the tuff rings, repeated hydromagmatic explosion cycles began with a series of intermittent tephra-finger explosions leading up to continuous uprush explosions which lasted for several minutes to several hours. This nozzle-like continuous activity produced eruption columns 100–250 m in diameter and 500–2000 m in height which probably quarried several hundred metres below the ground surface. The continuous-uprush explosion type provides a reasonable mechanism to excavate a diatreme from the top down. During construction of the tuff rings, concentric faults repeatedly downdropped a funnel-like structure (400–800 m in diameter) several hundred metres, thus accounting for the presence of subaerially deposited tephra in the drill core far beneath sea level. Ring dykes later intruded upward along these faults and fed small lava flows. Heat in the surface tephra probably originated primarily from these shallow intrusions.

Geological Magazine↗
USGS2009

The morphology and distribution of submerged reefs in the Maui-Nui Complex, Hawaii: New insights into their evolution since the Early Pleistocene

Reef drowning and backstepping have long been recognised as reef responses to sea-level rise on subsiding margins. During the Late Pleistocene (~500–14 ka) Hawaiian reefs grew in response to rapid subsidence and 120 m 100 kyr sea-level cycles, with recent work on the submerged drowned reefs around the big island of Hawaii, and in other locations from the last deglacial, providing insight into reef development under these conditions. In contrast, reefs of the Early Pleistocene (~1.8–0.8 Ma) remain largely unexplored despite developing in response to significantly different 60–70 m 41 kyr sea-level cycles. The Maui-Nui Complex (MNC — forming the islands of Maui, Molokai, Lanai and Kahoolawe), provides a natural laboratory to study reef evolution throughout this time period as recent data indicate the reefs grew from 1.1 to 0.5 Ma. We use new high resolution bathymetric and backscatter data as well as sub-bottom profiling seismic data and field observations from ROV and submersible dives to make a detailed analysis of reef morphology and structure around the MNC. We focus specifically on the south-central region of the complex that provides the best reef exposure and find that the morphology of the reefs varies both regionally and temporally within this region. Barrier and pinnacle features dominate the steeper margins in the north of the study area whilst broad backstepping of the reefs is observed in the south. Within the Au'au channel in the central region between the islands, closely spaced reef and karst morphology indicates repeated subaerial exposure. We propose that this variation in the morphology and structure of the reefs within the MNC has been controlled by three main factors; the subsidence rate of the complex, the amplitude and period of eustatic sea-level cycles, and the slope and continuity of the basement substrate. We provide a model of reef development within the MNC over the last 1.2 Ma highlighting the effect that the interaction of these factors had on reef morphology.

Hawai'i↗
USGS2009

Hand-hewn granite basins at Native American saltworks, Sierra Nevada, California

This site in the northern Sierra Nevada contains about 369 circular basins carved in fresh, glaciated granodioritic bedrock, with 325 basins crowded together in an area of 2,700 m 2 on the main terrace. These terrace basins have a median average diameter of 125 cm (80 percent between 100 and 160 cm) and a median depth of 75–80 cm. They show a strong congruity to similar granitic basins in the southern Sierra Nevada apparently of Native American origin that are generally shallower. The basins are not of natural origin, as indicated by uniformity in size and nonoverlapping character of the basins; their common arrangement in lineaments; details of the shape of the basins; features in common with granite basins in the Southern Sierra Nevada; and, most compelling, the clustering of all the basins adjacent to (within 20 m of) two saline streams fed from a nearby salt spring. Native Americans apparently excavated them for the purpose of collecting saline water to evaporate and make salt for their use, and also as an animal attractant and a trade commodity. The flow of the salty streams delivers about 2.9 metric tons of salt per summer season to the basin area, and evaporation rates and the holding capacity of the basins indicate that about 2.5 tons of salt could be produced per season. This correspondence shows that the Indians made enough basins to exploit the resource. The site is the most impressive prehistoric saltworks yet discovered in North America and represents a unique departure from traditional hunter-gatherer activities to that of manufacturing. The actual grinding of so many basins in granite could not have been done without the labor of a concentrated population. It is believed that the work was accomplished over a long time by many people and with the use of fire to help disaggregate the bedrock.

Scientific Investigations Report↗
USGS2009

Precision leveling and geodetic GPS observations performed on Surtsey between 1967 and 2002

The load on the crust from the ~ 0.8 km 3 of eruptive products of the Surtsey eruption is expected to lead to subsidence of the Surtsey island by sagging of the lithosphere, compaction of material, and slumping of the volcanic edifice. Immediately after the eruption ended in the summer of 1967 a levelling line was established across the island to monitor this expected subsidence. The line originally contained 42 benchmarks. As Surtsey is subjected to extensive erosion, in particular in the western and southern parts of the island, the western section of the line has been lost to the sea. In the year 2002 the line ended with benchmark 28. Additional benchmarks were installed 1979, 1982, 1985 and 2002, to fill in gaps in the original line and another profile was installed through the Surtur I crater. Between 1967 and 2002 levelling has been performed eleven times. One benchmark was surveyed with geodetic GPS in 1992. The benchmark was resurveyed in 2000 and 2002 and the GPS network has been extended to comprise four points. In this report we have compiled the levelling data collected on Surtsey so far. Furthermore we present coordinates for the GPS-benchmarks. Continuing subsidence of Surtsey is observed with a decaying rate. The area around the Surtur I crater is the most stable part with a subsidence rate of 0.7 cm/yr in the period 1991–2002. The largest subsidence is observed at the flanks of the island with rates up to 1.4 cm/yr. The excess rate here is most likely caused by slumping of the sides of the island.

Surtsey↗
USGS2008

Origin of meter-size granite basins in the southern Sierra Nevada, California

Meter-size granite basins are found in a 180-km belt extending south from the South Fork of the Kings River to Lake Isabella on the west slope of the southern Sierra Nevada, California. Their origin has long been debated. A total of 1,033 basins have been inventoried at 221 sites. The basins occur on bedrock granitic outcrops at a median elevation of 1,950 m. Median basin diameter among 30 of the basin sites varies from 89 to 170 cm, median depth is 12 to 63 cm. Eighty percent of the basin sites also contain smaller bedrock mortars (~1-2 liters in capacity) of the type used by Native Americans (American Indians) to grind acorns. Features that suggest a manmade origin for the basins are: restricted size, shape, and elevation range; common association with Indian middens and grinding mortars; a south- and west-facing aspect; presence of differing shapes in distinct localities; and location in a food-rich belt with pleasant summer weather. Volcanic ash (erupted A.D. 1240±60) in the bottom of several of the basins indicates that they were used shortly before ~760 years ago but not thereafter. Experiments suggest that campfires built on the granite will weaken the bedrock and expedite excavation of the basins. The primary use of the basins was apparently in preparing food, including acorns and pine nuts. The basins are among the largest and most permanent artifacts remaining from the California Indian civilization.

California↗
USGS2006

Drowned coralline algal dominated deposits off Lanai, Hawaii; carbonate accretion and vertical tectonics over the last 30 ka

We present detailed bathymetry, remotely operated vehicle (ROV) and submersible observations, and sedimentary and radiocarbon age data from carbonate deposits recovered from two submerged terraces at &minus; 150 m (T1) and &minus; 230 m (T2) off Lanai, Hawaii. The tops of the terraces are veneered by relatively thin (<5 m) in situ accumulations of coralline algal nodule, coralgal nodule, Halimeda and a derived oolitic facies deposited in intermediate (30&ndash;60 m) to deep fore-reef slope settings (60&ndash;120 m). The data are used to develop a sedimentary facies model that is consistent with eustatic sea-level variations over the last 30 ka. Both nodule facies on T1 and T2 initiated growth 30&ndash;29 ka following a fall in sea level of &sim;50 m and increase in bottom currents during the transition from Marine Isotope Stage 3 to 2. The nodules accreted slowly throughout the Last Glacial Maximum when sea-level was relatively stable. Drowning occurred during the early deglaciation (17&ndash;16 ka) and was marked by the complete drowning of coralline algal nodules facies on T2 and incipient drowning of coralgal facies on T1. Abrupt sea-level rise during the middle deglaciation, perhaps associated with global meltwater pulse 1A (14&ndash;15 ka), finally drowned the coralgal facies on T1, which in turn was overlain by a deep-water Halimeda facies or an oolitic facies derived from upslope. Our data indicates that Lanai has experienced relatively little vertical tectonic movement over the last 30 ka. Using paleobathymetric data derived from the sedimentary facies, age vs. depth relationships, and published sea-level curves, we estimate that Lanai could be either slowly uplifting or subsiding, but at rates <0.1 m/kyr (uplift) or <0.4 m/kyr (subsidence) over this 30 kyr period.

Hawai'i↗
USGS2006

King of the 40th parallel - Discovery in the American West

This book recounts the life and achievements of Clarence King, widely recognized as one of America’s most gifted intellectuals of the nineteenth century, and a legendary figure in the American West. King’s genius, singular accomplishments, and near-death adventures unfold in a narrative centered on his personal relationship with his lifelong friend and colleague, James Gardner. The two, upon completing their studies at Yale, traveled by wagon train across the continent and worked with the California Geological Survey. King went on to establish the Geological Exploration of the 40th Parallel, a government mapping program that stretched across the western mountain chains from California to Wyoming. This was the precursor to the U.S. Geological Survey (USGS). Founded in 1879, with Clarence King as its architect and first director, the USGS became the most important and influential science agency in the nation. The adventurous aspects of conducting geological fieldwork in the West, much of them documented by letters written by King and Gardner, punctuate a book copiously illustrated with historic maps and photographs showing localities and people important to the story.

Book↗
USGS2002

Volcanic breccia and hyaloclastite in blocks from the Nuuanu and Wailau landslides, Hawaii

Steep slopes of giant landslide blocks in the Nuuanu and Wailau landslides expose fragmental volcanic rocks subdivided into monomict and polymic t hyaloclastite and breccia. The various samples form as 1) secondary slopemantling unlithified polymict breccia consisting of clasts set in a mud matrix; 2 ) monomict and polymict hyaloclastite and polymict breccia, with zeolite cement, that form downslope of the shoreline where lava flows enter the sea; and 3 ) monomict breccia formed by tectonic fragmentation of glassy submarine-erupted pillow basalt. Lavas erupted from single volcanoes are highly variable in major-element composition, even during their tholeiitic shield stage, making it difficult to identify which landslide block was derived from which volcano. Low-temperature fluids circulate through the fragmental deposits on the flanks of the volcanoes, partially altering the glass to palagonite and cementing the volcaniclastic rocks with Na- and K-rich zeolites. Volcano spreading along low-angle thrust faults laterally transports deep early submarine pillow lava out to the flank of the volcano where it crops out as tectonic monomict breccia. The faults underlying the landslide blocks are within this tectonized core of the volcano, not simply within the shallow slope deposits of hyaloclastite and breccia. The Nuuanu landslide predates the 1.5 Ma Wailau landslide.

Hawaii↗
USGS2000

Formation of submarine flat-topped volcanic cones in Hawai'i

High-resolution bathymetric mapping has shown that submarine flat-topped volcanic cones, morphologically similar to ones on the deep sea floor and near mid-ocean ridges, are common on or near submarine rift zones of Kilauea, Kohala (or Mauna Kea), Mahukona, and Haleakala volcanoes. Four flat-topped cones on Kohala were explored and sampled with the Pisces V submersible in October 1998. Samples show that flat-topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage. Similarly shaped flat-topped cones on the northwest submarine flank of Ni'ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage. Submarine postshield-stage eruptions on Hilo Ridge, Mahukona, Hana Ridge, and offshore Ni'ihau form pointed cones of alkalic basalt and hawaiite. The shield stage flat-topped cones have steep (∼25°) sides, remarkably flat horizontal tops, basal diameters of 1–3 km, and heights <300 m. The flat tops commonly have either a low mound or a deep crater in the center. The rejuvenated-stage flat-topped cones have the same shape with steep sides and flat horizontal tops, but are much larger with basal diameters up to 5.5 km and heights commonly greater than 200 m. The flat tops have a central low mound, shallow crater, or levees that surrounded lava ponds as large as 1 km across. Most of the rejuvenated-stage flat-topped cones formed on slopes <10° and formed adjacent semicircular steps down the flank of Ni'ihau, rather than circular structures. All the flat-topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades. These, and other submarine volcanic cones of similar size and shape, apparently form as continuously overflowing submarine lava ponds. A lava pond surrounded by a levee forms above a sea-floor vent. As lava continues to flow into the pond, the lava flow surface rises and overflows the lowest point on the levee, forming elongate pillow lava flows that simultaneously build the rim outward and upward, but also dam and fill in the low point on the rim. The process repeats at the new lowest point, forming a circular structure with a flat horizontal top and steep pillowed margins. There is a delicate balance between lava (heat) supply to the pond and cooling and thickening of the floating crust. Factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents, moderate to high confining pressure at moderate to great ocean depth, long-lived steady eruption (years to decades), moderate effusion rates (probably ca. 0.1 km 3 /year), and low, but not necessarily flat, slopes. With higher effusion rates, sheet flows flood the slope. With lower effusion rates, pillow mounds form. Hawaiian shield-stage eruptions begin as fissure eruptions. If the eruption is too brief, it will not consolidate activity at a point, and fissure-fed flows will form a pond with irregular levees. The pond will solidify between eruptive pulses if the eruption is not steady. Lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones, as occurs during the post-shield stage. The steady effusion of lava on land constructs lava shields, which are probably the subaerial analogs to submarine flat-topped cones but formed under different cooling conditions.

Hawaii↗
USGS2000

Geological monitoring of Surtsey, Iceland, 1967-1998

Aspects of the geological monitoring of the volcanic island of Surtsey 1967-1998, are described. A hydrothermal system was developed within the tephra craters in late 1966 to early 1967. Temperatures in a drill hole, situated at the eastern border of the hydrothermal area, indicate that the hydrothermal system at that site has been cooling at an average rate of &le; 1&deg;C per year since 1980. The tephra was altered rapidly within the hydrothermal area, producing the first visible palagonite tuff in 1969. A substantial part of the tephra pile above sea level was probably converted to tuff by 1972. The visible area of tuff has gradually increased since then, primarily due to erosion of tephra at the surface. By 1998 52% of the exposed tephra area had been converted to palagonite tuff. By volume, however, some 80-85% of the tephra pile above sea level has been converted to tuff in 1998. The area of Surtsey has shrunk from its original 2.65 km 2 (1967) to 1.47 km 2 (1998) due to marine abrasion. The geological formations on Surtsey have, however, responded quite variably to erosion. The tephra pile was easily eroded, but marine abrasion. The central core of palagonite tuff is estimated to be &le;0.39 km 2 . Statistical estimation of models of the decreases of Surtsey indicate that it will last for a long time. The numerical experiments indicate that it will take over 100 years until only the palagonite tuff core is left. It is postulated that the final remnany of Surtsey before complete destruction will be a palagonite tuff crag, comparable to those of the other islands in the Vestmannaeyjar archipelago.

Surtsey↗
USGS1995

Petrology of Submarine Lavas from Kilauea's Puna Ridge, Hawaii

We have studied 30 quenched tholeiitic lava flows recovered by 20 dredge hauls and one submersible dive along Puna Ridge, the submarine part of the East Rift Zone of Kilauea Volcano, Hawaii Glass grains from numerous additional flows were recovered in turbidite sands cored in the Hawaiian Trough. These quenched lavas document variable primary magma compositions; olivine and multiphase crystallization and fractionation; degassing; wall-rock stoping and assimilation; mixing in the crustal reservoir and the rift zone; entrainment of olivine xenocrysts from a hot, ductile, olivine cumulate body; and disruption of gabbro wallrocks in the rift zone. Glass grains in turbidite sands contain up to 15⋅0wt% MgO, in contrast to < 7⋅0wt% MgO for the sampled glass rinds on lavas. The most forsteritic olivine phenocryst (F0 90·7 ) is in equilibrium with primary Kilauea liquid containing an average 16⋅5 wt% MgO, but ranging from 13⋅4 to 18⋅4%. Lavas and glass grains have more restricted P 2 O 5 /K 2 O and TiO 2 /K 2 O than glass inclusions in olivine, because more diverse liquids trapped as glass inclusions are mixed and homogenized before eruption. Variable trace element compositions in glass grains and whole rocks indicate that the primary liquids form by partial melting of mantle sources retaining clinopyroxene and garnet. Orthopyroxene xenocrysts formed at moderate pressures provide evidence for a sub-crustal staging zone. Chromite and olivine crystallize in the crustal magma reservoir as the liquid cools from an average 1346°C to ∼1170°C. Low viscosities of the primary liquids (0·4 Pas) facilitate olivine settling, and the crystallized olivine forms an olivine cumulate body at the base of the reservoir. Olivine is deformed as the hot ductile dunite body flows down and away from the summit. This flow drives instability of the Hilina landslide on Kilauea. Dikes intrude the dunite, and magma flowing through the dikes disaggregates and entrains olivine xenocrysts in Puna Ridge magmas. Primary liquids pond at or near the base of Kilauea's crustal reservoir because they are denser than more fractionated liquids that occupy the upper parts of the reservoir. The sulfur and water contents of glass rinds indicate that fractionated liquids near the top of the reservoir degas at low pressure, a process that increases their density and causes them to sink to levels where they mix with resident undegassed, near-primary liquid. The fractionated liquids near the top of the magma reservoir acquire excess Cl, owing to assimilation of hydrothermally altered roofrocks. Magma flowing into the rift zone encounters and mixes with low-temperature, multiphase-fractionated melt. The mixed magmas typically contain rare orthopyroxene, plagioclase as sodic as andesine, olivine as fayalitic as F0 75 and Fe-rich augite derived from the fractionated magma. Magma flowing through dikes also dislodged fragments of gabbroic wallrocks that occur as xenoliths. The interrelations in the Kilauean submarine lavas between host glass and glass inclusion compositions, volatile contents and mineral chemistry reveal an extraordinarily complex sequence of petrogenetic processes and events that are difficult or impossible to determine in subaerial Kilauea lavas because of crystallization, reequilibration and degassing during or after their eruption.

Hawaii↗
USGS1995

Intraglacial volcanism in the Wells Gray–Clearwater volcanic field, east-central British Columbia, Canada

Small-volume, subaerial, subaqueous and subglacial basaltic eruptions occurred in the Wells Gray–Clearwater area during Quaternary time. Part of this time, significant thicknesses of glacial ice were present. Dating of intraglacial volcanic features corroborates other evidence of an Early Pleistocene, Cordilleran-wide ice sheet. Of the intraglacial volcanoes investigated, three were studied in detail and of these, two probably erupted during the Fraser glaciation (11–20 ka), when maximum ice level exceeded 2100 m elevation. Major-element and sulphur concentrations were measured in glass from the volcanoes to provide insight into vent conditions at the time of eruption. Hyalo Ridge (2102 m elevation, whole-rock K–Ar age of 0.02 ± 0.01 Ma) is a small volcanic edifice capped by lava flows with coherent pillowed lavas and interbedded hyaloclastite exposed over nearly 400 m altitude on its east flank. Low sulphur content (<0.03 wt.%) in pillow rim glasses indicates that the lavas are degassed. It is interpreted that the vent built above the water (or ice) surface then fed lava flows that crossed a shoreline and produced pillowed flows. Pyramid Mountain is a volcanic cone 240 m high, comprised of glassy, vesicular, lapilli-tuff breccia. The highly alkalic glass contains 0.1 wt.% S (considered high), and indicates a high original volatile content and drastic quenching, probably during phreatomagmatic eruption from a meltwater-flooded vent. East of the Clearwater River a sequence of massive pillowed flows and pillow joint-block breccias is exposed from 880 to 1320 m elevation (0.27 ± 0.05 Ma). The vent location is unknown. Moderate S content (0.040–0.055 wt.%) indicates that the lavas were erupted in shallow water and are largely degassed. The S content of glass in dykes cutting the pillow breccias is low. The dykes are interpreted as lava that has flowed laterally or down into cracks

British Columbia↗