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USGS2009

The National Map - Elevation

The National Elevation Dataset (NED) is the primary elevation data product produced and distributed by the USGS. The NED provides seamless raster elevation data of the conterminous United States, Alaska, Hawaii, and the island territories. The NED is derived from diverse source data sets that are processed to a specification with a consistent resolution, coordinate system, elevation units, and horizontal and vertical datums. The NED is the logical result of the maturation of the long-standing USGS elevation program, which for many years concentrated on production of topographic map quadrangle-based digital elevation models. The NED serves as the elevation layer of The National Map, and provides basic elevation information for earth science studies and mapping applications in the United States. The NED is a multi-resolution dataset that is updated bimonthly to integrate newly available, improved elevation source data. NED data are available nationally at grid spacings of 1 arc-second (approximately 30 meters) for the conterminous United States, and at 1/3 and 1/9 arc-seconds (approximately 10 and 3 meters, respectively) for parts of the United States. Most of the NED for Alaska is available at 2-arc-second (about 60 meters) grid spacing, where only lower resolution source data exist. Part of Alaska is available at the 1/3-arc-second resolution, and plans are in development for a significant upgrade in elevation data coverage of the State over the next 5 years. Specifications for the NED include the following: *Coordinate system: Geographic (decimal degrees of latitude and longitude), *Horizontal datum: North American Datum of 1983 (NAD 83), *Vertical datum: North American Vertical Datum of 1988 (NAVD 88) over the conterminous United States and varies in other areas, and *Elevation units: Decimal meters.

Fact Sheet↗

USGS2005

2003 volcanic activity in Alaska and Kamchatka: Summary of events and response of the Alaska Volcano Observatory

The Alaska Volcano Observatory (AVO) monitors the more than 40 historically active volcanoes of the Aleutian Arc. Of these, 24 were considered monitored in real time with short-period seismic instrument networks as of the end of 2003. The AVO core monitoring program also includes daily analysis of satellite imagery, observation over flights, and compilation of pilot reports and reports from local residents and mariners. In 2003, AVO responded to eruptive activity or suspected volcanic activity at or near 10 volcanic centers: Wrangell, Redoubt, Iliamna, Augustine, Mageik, Veniaminof, Pavlof, Emmons Lake (Hague), Shishaldin, and Akutan volcanoes. In addition to responding to eruptive activity at Alaska volcanoes, AVO assisted in the dissemination of information for the Kamchatka Volcanic Eruption Response Team (KVERT) about the 2003 activity of 6 Russian volcanoes: Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, Alaid, and Chikurachki volcanoes. Due to prevailing wind directions, erupting Kamchatkan, Kurile Island, and Alaskan volcanoes pose a serious potential threat to aircraft in the North Pacific.

Alaska↗

USGS2015

Coral 13C/12C records of vertical seafloor displacement during megathrust earthquakes west of Sumatra

The recent surge of megathrust earthquakes and tsunami disasters has highlighted the need for a comprehensive understanding of earthquake cycles along convergent plate boundaries. Space geodesy has been used to document recent crustal deformation patterns with unprecedented precision, however the production of long paleogeodetic records of vertical seafloor motion is still a major challenge. Here we show that carbon isotope ratios ( ) in the skeletons of massive Porites corals from west Sumatra record abrupt changes in light exposure resulting from coseismic seafloor displacements. Validation of the method is based on the coral response to uplift (and subsidence) produced by the March 2005 M w 8.6 Nias–Simeulue earthquake, and uplift further south around Sipora Island during a M&sim;8.4 megathrust earthquake in February 1797. At Nias, the average step-change in coral was 0.6±0.1&permil;/m for coseismic displacements of +1.8 m and −0.4 m in 2005. At Sipora, a distinct change in Porites microatoll growth morphology marks coseismic uplift of 0.7 m in 1797. In this shallow water setting, with a steep light attenuation gradient, the step-change in microatoll is 2.3&permil;/m , nearly four times greater than for the Nias Porites . Considering the natural variability in coral skeletal , we show that the lower detection limit of the method is around 0.2 m of vertical seafloor motion. Analysis of vertical displacement for well-documented earthquakes suggests this sensitivity equates to shallow events exceeding M w &sim;7.2 in central megathrust and back-arc thrust fault settings. Our findings indicate that the coral paleogeodesy technique could be applied to convergent tectonic margins throughout the tropical western Pacific and eastern Indian oceans, which host prolific coral reefs, and some of the world's greatest earthquake catastrophes. While our focus here is the link between coral , light exposure and coseismic crustal deformation, the same principles could be used to characterize interseismic strain during earthquake cycles over the last several millennia.

Earth and Planetary Science Letters↗

USGS1999

Geological and geophysical setting of the gold-silver vein systems of Unga Island, southwestern Alaska

The topic of this CD-ROM is the geologic framework of gold-silver vein deposits on Unga Island, in the Shumagin Islands, southwestern Alaska. The core of the publication is a new geologic map at a scale of 1:63,360 and aeromagnetic and electromagnetic survey data acquired by industry over the area of mineralization. Both the geologic map as well as a preliminary interpretation of the geophysical data - which are included by permission of the owner - are aimed towards deciphering the relations among volcanism, tectonism, and mineralization. Data and discussions are organized in seven chapters, titles of which are outlined in the table of contents. The chapters consist of viewable text and figure images; postscript versions of the frontispiece figures and all chapter figures are included on the CD-ROM as well. The geologic map is a large viewable figure (Plate 1) that accompanies chapter 2. The map was constructed in ARC and its component coverages are provided in the folder 'Geology' for users who may wish to modify the geologic data or add their own data.

Alaska↗

USGS2019

Petrology of the 2016–2017 eruption of Bogoslof Island

The 2016–2017 eruption of Bogoslof primarily produced crystal-rich amphibole basalts. The dominant juvenile tephra were highly microlitic with diktytaxitic vesicles, and amphiboles had large reaction rims. Both observations support a magma history of slow ascent and/or shallow stalling prior to eruption. Plagioclase-amphibole-clinopyroxene mineralogy are also suggestive of shallow magma crystallization. Lavas were emplaced as shallow submarine lava domes and cryptodomes that produced 70 relatively short-lived and water-rich explosions over the course of the 9-month long eruption. The explosions ejected older trachyandesite lavas that were likely uplifted by cryptodome emplacement that began in December 2016 and continued for many months. Trachyte pumice, similar in composition to a 1796 lava dome, was entrained in basalts by the end of the eruption. The pumice appears to be a largely crystalline magma that was rejuvenated, entrained in the basalt, and heated to ~1000 ℃. The composition of trachytes require differentiation through stronger amphibole control than the apparent shallow crustal evolution implied for the basalt. This suggests that they are magmas derived from a mid-crustal zone of amphibole crystallization. Nearby arc-front volcanoes that notably lack amphibole have strikingly similar compositional trends. Trace element signatures of the Bogoslof basalts, however, suggest derivation from a mantle source with residual garnet and lower-degree melting than basalts from nearby arc-front volcanoes. The diversity of magmas erupted at Bogoslof thus provides an opportunity not only to probe rare backarc compositions from the Aleutian arc, but also to examine the apparent role of amphibole in generating evolved compositions more broadly in arc environments.

Alaska↗

USGS2012

Geophysical constraints on Washington convergent margin structure

Gravity and magnetic maps of western Washington reveal the lateral structure and fabric of the Washington Coast Range, Puget Basin, and southern Washington Cascade Range. The magnetic and gravity maps show large amplitude positive anomalies associated with the shallow but largely buried section of Washington Coast Range mafic rocks which are separated by negative anomalies over deep sedimentary basins. The positive anomalies indicate that the Coast Range mafic basement extends farther east than previously thought, at least as far east as the longitude of Seattle. Linear and steep gravity and magnetic gradients indicate many unmapped, often buried faults in the Washington Coast Range Province. Magnetic highs are also associated with mapped batholiths in the Cascade arc. Several magnetic highs observed east of the Coast Range rocks and west of these batholiths may be associated with buried Tertiary plutons or ophiolites. Two-dimensional gravity and magnetic modeling constrained with geological and other geophysical data indicate that the Coast Range Province rocks are about 1 km thick at the coast, thickening to as much as 30 km near their postulated eastern edge. A maximum boundary on the average density of the upper 15–20 km of the rocks that compose the Coast Range Province of 2920 kg/m 3 was established by the modeling, suggesting a composition largely of basalt and gabbro with little interbedded sediments. Under these rocks may be mantle or a subduction complex composed of dense mafic, ultramafic, and sedimentary rocks like that proposed to underlie Vancouver Island. Previous gravity models of the Washington margin include lower densities for the proposed subduction complex than for Vancouver Island, suggesting a lower component of mafic and ultramafic rocks than the rocks underlying Vancouver Island. However, my Washington model requires that the proposed subduction complex be more dense than the trench sediments and, therefore, that material denser than sediments be incorporated within it. The absence of continental mantle and the modeled wedge shape of the Coast Range Province upper crust suggest that erosion of the bottom of the overriding plate by subduction processes may have occurred.

Washington↗

USGS2022

Interaction between climate and tectonics in the northern Lesser Antilles inferred from the last interglacial shoreline on Barbuda island

In the context of increasing evidence of plate interface coupling variability in subduction zones, there is a need to extend the short time window given by instrumental data and to gather data over multiple time and spatial scales. We hence investigated the long-term topography on Barbuda island, located in the northern part of the Lesser Antilles, west of the Caribbean subduction zone. Following pioneering work using a set of marine terraces on the eastern side of the island, we performed the first U-Th dating on 10 corals in growth position from the lowest terrace, for which the highest relative sea-level (RSL) indicator is found at 9 ± 1 m above the mean sea level. We find that this terrace corresponds to the Last Interglacial (LIG) (ages between 122.8 ± 0.3 ka and 128.1 ± 0.3 ka) and we estimate a paleo RSL of 7 ± 2 m above the current mean sea level. The present elevation of the LIG shoreline on Barbuda might imply tectonics as an additional mechanism to eustatic sea level, mantle dynamic topography and glacial isostatic adjustment. East-west morphological asymmetry of Barbuda and difference in LIG shoreline elevation between Barbuda and Antigua suggest a regional tectonic process. As with the proposed westward tilting from the forearc to the volcanic arc of the Guadeloupe archipelago, vertical deformation on Barbuda could be related to plate-scale subduction processes. Long-term uplift of Barbuda might be related to the accumulation of residual coseismic deformation not fully recovered by interseismic subsidence and the corresponding seismogenic segment would extend below the Moho.

Geochemistry, Geophysics, Geosystems↗

USGS1983

Rare-earth element geochemistry and the origin of andesites and basalts of the Taupo Volcanic Zone, New Zealand

Two types of basalt (a high-Al basalt associated with the rhyolitic centres north of Taupo and a "low-Al" basalt erupted from Red Crater, Tongariro Volcanic Centre) and five types of andesite (labradorite andesite, labradorite-pyroxene andesite, hornblende andesite, pyroxene low-Si andesite and olivine andesite/low-Si andesite) occur in the Taupo Volcanic Zone (TVZ), North Island, New Zealand. Rare-earth abundances for both basalts and andesites are particularly enriched in light rare-earth elements. High-Al basalts are more enriched than the "low-Al" basalt and have values comparable to the andesites. Labradorite and labradorite-pyroxene andesites all have negative Eu anomalies and hornblende andesites all have negative Ce anomalies. The former is probably due to changing plagioclase composition during fractionation and the latter to late-stage hydration of the magma. Least-squares mixing models indicate that neither high-Al nor "low-Al" basalts are likely sources for labradorite/labradorite-pyroxene andesites. High-Al basalts are considered to result from fractionation of olivine and clinopyroxene from a garnet-free peridotite at the top of the mantle wedge. Labradorite/labradorite-pyroxene andesites are mainly associated with an older NW-trending arc. The source is likely to be garnet-free but it is not certain whether the andesites result from partial melting of the top of the subducting plate or a hydrated lower portion of the mantle wedge. Pyroxene low-Si andesites probably result from cumulation of pyroxene and calcic plagioclase within labradorite-pyroxene andesites, and hornblende andesites by late-stage hydration of labradorite-pyroxene andesite magma. Olivine andesites, low-Si andesites and "low-Al" basalts are related to the NNE-trending Taupo-Hikurangi arc structure. Although the initial source material is different for these lavas they have probably undergone a similar history to the labradorite/labradorite-pyroxene andesites. All lavas show evidence of crustal contamination. ?? 1983.

Chemical Geology↗

USGS2009

Three‐dimensional model of Hellenic Arc deformation and origin of the Cretan uplift

[1] The Hellenic Arc of Greece is the most seismically active part of Europe, but little is know about its mechanics. We modeled deformation along the arc using a finite element model. The model was intended to capture large‐scale 3‐D structure of Nubian plate subduction beneath the Aegean block and its deformational consequences. The shape of the interface was developed using mapped traces at the surface and earthquake hypocenters at depth. Model block motions were constrained by recent compilations of GPS velocity vectors. We simulated a 10 ka period of convergence between Nubia and the Aegean and calculated the strain field in the overriding plate as well as the spatial distribution and orientation of differential stress (∣ σ 1 − σ 3 ∣). From these calculations we derived testable quantities such as the expected seismic moment rate on the interplate contact, uplift pattern, and distribution of strain modes. Our relatively simple model broadly reproduced observed uplift patterns, earthquake activity, and loci of extension and contraction. The model showed a localization of uplift near the island of Crete, where the fastest Aegean uplift rates are well documented. Comparison of calculated expected seismic moment and observed earthquake catalogs implies a nearly fully coupled interplate contact. On the basis of our modeling results, we suggest that south Aegean deformation is driven primarily by the fast moving (∼33 mm a −1 ) Aegean upper plate overriding a nearly stalled (∼5 mm a −1 ) Nubian lower plate. This tectonic setting thus more closely resembles a continental thrust than it does a typical oceanic subduction zone.

Aegean Sea, Hellenic Arc↗

USGS2000

Geologic map of the Wildcat Lake 7.5' quadrangle, Kitsap and Mason Counties, Washington

The Wildcat Lake quadrangle lies in the forearc of the Cascadia subduction zone, about 20-km east of the Cascadia accretionary complex exposed in the Olympic Mountains (Tabor and Cady, 1978),and about 100-km west of the axis of the Cascades volcanic arc. The quadrangle lies near the middle of the Puget Lowland, which typically has elevations less than 600 feet (183 m), but on Gold Mountain, in the center of the quadrangle, the elevation rises to 1761 feet (537 m). This anomalously high topography also provides a glimpse of the deeper crust beneath the Lowland. Exposed on Green and Gold Mountains are rocks related to the Coast Range basalt terrane. This terrane consists of Eocene submarine and subaerial tholeiitic basalt of the Crescent Formation, which probably accreted to the continental margin in Eocene time (Snavely and others, 1968). The Coast Range basalt terrane may have originated as an oceanic plateau or by oblique marginal rifting (Babcock and others, 1992), but its subsequent emplacement history is complex (Wells and others, 1984). In southern Oregon, onlapping strata constrain the suturing to have occurred by 50 Ma; but on southern Vancouver Island where the terrane-bounding Leech River fault is exposed, Brandon and Vance (1992) concluded suturing to North America occurred in the broad interval between 42 and 24 Ma. After emplacement of the Coast Range basalt terrane, the Cascadia accretionary complex,exposed in the Olympic Mountains west of the quadrangle,developed by frontal accretion and underplating (e.g., Clowes and others, 1987). The Seattle basin, part of which lies to the north of Green Mountain, also began to develop in late Eocene time due to forced flexural subsidence along the Seattle fault zone (Johnson and others, 1994). Domal uplift of the accretionary complex beneath the Olympic Mountains occurred after approximately 18 million years ago (Brandon and others, 1998). Ice-sheet glaciation during Quaternary time reshaped the topography of the quadrangle, and approximately two-thirds of the map area is covered with Quaternary deposits related to the last glaciation. Geophysical studies and regional mapping indicate the Seattle fault lies north of Green Mountain. This fault produced a large earthquake about 1000 years ago and may pose a significant earthquake hazard (Bucknam and others, 1992; Atwater and Moore, 1992; Karlin and Abella,1992; Schuster and others, 1992; Jacoby and others, 1992). We found no evidence of Holocene faulting in the Wildcat Lake quadrangle. Geologic mapping within and marginal to the quadrangle began with Willis (1898), who described glacial deposits in Puget Sound. Weaver (1937) correlated volcanic rocks in the quadrangle to the Eocene Metchosin Volcanics on Vancouver Island. Sceva (1957), Garling and Moleenar (1965), and Deeter (1978) all focused on mapping and understanding the Quaternary stratigraphy of the Kitsap Peninsula, but they also examined bedrock in the quadrangle. Reeve (1979) was the first to examine the igneous rocks on Green and Gold Mountains in some detail, and Clark (1989) significantly improved Reeve's (1979) mapping. Clark's (1989) mapping was conducted soon after extensive logging on the mountains. A surficial geologic map of the Seattle 1:100,000-scale quadrangle, which includes the Wildcat Lake 1:24,000-scale quadrangle, was published by Yount and others (1993). Yount and Gower (1991) also published a bedrock geologic map of the Seattle quadrangle. Geologic mapping for this report was conducted by Haeussler in the spring and summer of 1998 and in the winter of 1999. We could not substantially improve upon the bedrock mapping of Clark (1989) and thus it is incorporated into this map. Well data in the southeastern corner of the map area also helped to constrain the surficial mapping (Geomatrix Consultants, 1997). In addition, 1995 vintage 1:12,000-scale aerial photographs were used in mapping Quaternary deposits. Geologic time scale is that of Berggeren and others (1995).

Washington↗

USGS2000

Geologic studies in Alaska by the U.S. Geological Survey, 1997

The eight papers that follow continue the series of U.S. Geological Survey (USGS) reports on investigations in the geologic sciences in Alaska. The series presents new and sometimes preliminary findings that are of interest to earth scientists in academia, government, and industry; to land and resource managers; and to the general public. Reports presented in Geologic Studies in Alaska cover a broad spectrum of topics from all parts of the State (fig. 1), which serves to emphasize the diversity of USGS efforts to meet the Nation's needs for earth-science information in Alaska. The papers in this volume are organized under the topics Resources, Geologic Framework, and Environment and Climate. Such an organization is intended to reflect the scope and objectives of USGS programs currently active in Alaska. Resource papers include one that presents detailed observations from a Mississippian Zn-Pb-Cu-Ag occurrence in the Brooks Range (Werdon). Mineralogic, chemical, and isotopic data provide the basis for a proposed relationship between this vein-breccia deposit and the shale-hosted massive sulfide deposit type, which includes the active Red Dog mine in the western Brooks Range. Also included under the topic of Resources is a paper that presents geochemical and isotopic data from the Greens Creek and Woewodski Island volcanogenic massive sulfide deposits in southeastern Alaska (Newberry and Brew). The depositional environment and sedimentological setting of Tertiary coal beds in the Matanuska and Susitna Valleys is the focus of a third paper under the topic of Resources (Flores and others). Geologic Framework studies provide background information that is the scientific basis for present and future studies of the environment, mineral and energy resources, paleoclimate, and hazards in Alaska. One paper presents the results of sedimentologic and paleontologic comparisons of lower Paleozoic, deep-water-facies rock units in central Alaska (Dumoulin and others). The authors show which of these units are likely to correlate with one another, suggest likely source regions, and provide a structural restoration of units that have been fragmented by large fault motions. A second framework paper provides a map, rock descriptions, and chemical compositions of volcanic rocks in a newly recognized, geologically young volcanic center in the Aleutian volcanic arc (Hildreth and others). A third paper presents an interesting summary of gravity changes that occurred in south-central Alaska during the great earthquake of 1964 and for the following 25 years (Barnes). Gravity changes correlate with land-elevation changes in some cases, but not in others, which means that different processes are responsible for the gravity changes.

Alaska↗

USGS1946

Geology and ground-water resources of the island of Hawaii

Hawaii, the largest island in the Hawaiian group, is 93 miles long, 76 miles wide, and covers 4,030 square miles. Mauna Loa Volcano is 13,680 feet high and Mauna Kea is 13,784 feet high. Plate 1 shows the geology, wells, springs, and water-development tunnels. Plate 2 is a map and description of points of geologic interest along the main highways. Plate 3 (same sheet as plate 2) shows highways and points of geologic interest in Hawaii National Park area. The volcanic terms used in the report are defined. Hawaii was built by five volcanoes. All the rocks are volcanic, except for minor amounts of sedimentary rock derived from them. Mauna Loa and Kilauea volcanoes erupt often; Hualalai Volcano last erupted in 1801; Mauna Kea has had Recent but no historic eruptions; Kohala Mountain has long been extinct. Kohala Mountain constitutes the northern end of the island. It is built largely of rocks of the Pololu volcanic series which are dominantly olivine basalt with a few thin intercalated beds of vitric basaltic ash. After the eruption of this series, Kohala Volcano was deeply eroded on the windward (northeastern) side, and a deep soil formed on its other slopes. Later, oligoclase andesite and trachyte lava flows, named the Hawi volcanic series, were erupted. They rest on soil at the top of the Pololu series, and lie in the valleys cut into the Pololu lavas on the windward slope. Both the Pololu and Hawi volcanics were erupted from three rift zones trending N. 35° W., S. 65° E., and S. 50° W. from the summit of the mountain. The rift zones are marked at the surface by rows or cinder cones, and beneath the surface by innumerable dikes. A caldera occupied the summit of the mountain at the beginning of the eruption of the Hawi lavas, and for a time confined the flows. It was gradually filled and the lava escaped northeastward into the large valleys. Some of the caldera faults can still be traced. A shallow graben indents the summit now. South of Kohala Mountain lies the much larger volcano of Mauna Kea. The early rocks of Mauna Kea constitute the Hamakua volcanic series. The lower member of this series consists chiefly of olivine basalt flows with intercalated thin beds of vitric basaltic ash. The olivine basalt of the lower member changes gradationally into the upper member, in which basalt and olivine basalt arc still abundant, but andesite also is present. Lavas of the upper member interfinger with Hawi lavas of Kohala Mountain. The Hamakua volcanic series is mantled with Pahala ash 5 to 20 feet thick, above which lie the rocks of the Laupahoehoe volcanic series. Locally the two series are separated by erosional unconformity, The Laupahoehoe lavas are dominantly andesite. The andesites erupted after the last glacial epoch are mapped separately on plate 1. The Laupahoehoe volcanic series, and probably also the Hamakua volcanic series, were erupted principally from three rift zones, trending west, northeast and south-southeast from the summit of the mountain. The upper slopes are studded with many large cinder cones, lying principally along the rift zones. Late in its geologic history, Mauna Kea was capped by a small glacier, presumably contemporaneous with the Wisconsin stage of glaciation in North America, which left conspicuous terminal, lateral, and ground moraines. Deposits exposed in canyons on the southern slope, formerly believed to be of glacial origin, are now believed to be volcanic explosion breccias. The main bulk of Hualalai Volcano is built of basalts of the Hualalai volcanic series. One flow of andesite has been found. The cinder and spatter cones lie principally along three rift zones which trend northwest, north, and southeast from the summit. On the northern slope of Hualalai Volcano lies the large trachyte pumice cone of Puu Waawaa, and its thick flow of trachyte. These are grouped together as the Waawaa volcanics. They are partly buried by later basalts from both Hualalai and Mauna Loa. The last eruption of Hualalai Volcano, in 1800–1801, produced olivine basalt. The earliest exposed rocks of Mauna Loa comprise the Ninole volcanic series. Several beds of altered vitric ash are intercalated with the lavas. Following eruption of the Ninole series, a long period or quiescence occurred, during which deep amphitheater-headed valleys were cut. This was followed by the eruption of the Kahuku volcanic series, consisting mostly of lavas with some thin beds of ash. The Rahuku series is overlain by the Pahala ash, which overlies also the Hilina volcanic series on Kilauea, the Hamakua volcanic series on Mauna Kea, and the Hawi volcanic series on Kohala, providing a rough datum for correlation of the lavas of the four mountains. Deposition of the Pahala ash was followed on Mauna Loa by eruption of the Kau volcanic series, which has continued until the present time. The historic and flaws of the Kau series are mapped separately on plate 1. The historic eruptions and volcanic activity of Mauna Loa are briefly described. The western and southern slopes of Mauna Loa are cut by normal faults along which the lower flanks of the mountain have slipped seaward. The Kau volcanic series and presumably also the Kahuku and Ninole volcanic series were erupted principally from vents along two rift zones which extend northeast and southwest from the summit caldera. The lavas of all three series are preponderantly olivine basalt. Many of the lavas contain small amounts of hypersthene. The Pahala ash on the northeastern and eastern slopes of Mauna Loa was derived largely from Mauna Kea. West and south of Kilauea Caldera, however, it was derived principally from Kilauea. Minor amounts were contributed by eruptions of Mauna Loa. It is a vitric basaltic ash, now generally altered to palagonite. The earliest exposed lavas and thin intercalated ash beds of Kilauea Volcano comprise the Hilina volcanic series. These are capped by the Pahala ash, which in turn, is overlain by the lavas and thin ash beds of the Puna volcanic series. The volcanics of both series were erupted along two rift zones, one extending southwestward from Kilauea Caldera, and the other extending southeastward for 5 miles and then bending sharply east by north. The lavas of both series are very largely olivine basalt. A few flows contain hypersthene. Augite phenocrysts are common in Mauna Loa lavas, but rare in those of Kilauea, indicating that crystallization has not progressed as far in the magma chamber of Kilauea Volcano as in that of Mauna Loa. Eruption of the Puna volcanic series has continued until the present time, the historic flows being separated from the prehistoric ones on plate 1. The historic eruptions and volcanic activity of Kilauea are briefly described. Kilauea Volcano originated on the southern slope of Mauna Loa where faults intersected the Eastern Fundamental Fissure of the Hawaiian Archipelago. The southern flank of Kilauea is cut by normal faults, along which the southern part is sliding seaward. The volcanoes of the island of Hawaii are believed to have started their activity in the Tertiary period. The great erosional period which followed deposition of the Pololu and Ninole volcanic series is placed near the end of the Pliocene. The Hilina and Hamakua volcanic series were probably erupted in the late Pliocene and earlier Pleistocene. The Hawi volcanic series and the Waawaa volcanics are probably early or middle Pleistocene in age. The main period of deposition of the Pahala ash was probably late in the middle Pleistocene or early in the upper Pleistocene. The Laupahoehoe volcanic series is late Pleistocene and Recent in age, most of the flows antedating the Wisconsin glaciation. The Hualalai volcanic series probably extends from Tertiary to historic time, and the Kau and Puna volcanic series from late Pleistocene to the present. A chapter is devoted to the petrography of the rocks in which are listed all reliable chemical rock analyses. The rocks of the island are highly permeable. Most of the rainfall sinks quickly into the ground. Perennial streams are present only on the windward slopes of Kohala Mountain and Mauna Kea. Most of the water sinks rapidly to the basal water table, where it floats on salt water according to the Ghyben-Herzberg principle. Basal water escapes in springs at or near sea level all along the coast. Only a very small proportion of it is recovered in wells. Along the windward coasts the basal water is of good quality and large supplies await development. Along the leeward coasts most of the basal water is brackish. In Kohala Mountain, much water is perched on ash beds in the Pololu volcanic series and on ash and soil at the base of the Hawi volcanic series. It escapes in perched springs in the big valleys and along the windward sea cliff and is recovered in tunnels. Along the windward slope of Mauna Keu, small amounts of water are perched by ash beds and dense lava flows in the Hamakua volcanic series. Small perched springs issue from these structures and water is recovered by tunnels. In the Kau District ash beds perch considerable water, which is recovered by many tunnels. On the southern slope of Mauna Kea small springs are perched by beds of hill wash. Dikes in the rift zones are relatively impermeable, but enclose masses of permeable rock. Water is confined at high level in the interdike compartments in Kohala Mountain, and probably in the other volcanoes. It escapes in high-level springs in the deep valleys on Kohala Mountain; some of it is recovered by tunnels. It is estimated that an average of about 13,085 million gallons of water a day falls as rain over the whole island. Of this only about 2.5 percent is visibly discharged from wells, tunnels, and springs. Large supplies of basal groundwater await development. Projects for development of additional water for the city of Hilo and the Kona District are described. Chemical analyses of water, water supplies of towns and villages, descriptions of wells, springs, and tunnels, and discharge records of numerous springs and tunnels are given in tabulated form.

Hawaii↗

USGS2020

Relocated aftershocks and background seismicity in eastern Indonesia shed light on the 2018 Lombok and Palu earthquake sequences

High seismicity rates in eastern Indonesia occur due to the complex interaction of several tectonic plates which resulted in two deadly, destructive earthquake sequences that occurred in Lombok Island and the city of Palu, Sulawesi in 2018. The first sequence began in July with an M w 6.4 event near Lombok, culminating in an M w 7.0 event 8 d later. This was then followed by a nearby M w 6.9 event 12 d later. Approximately 1000 km to the northeast, a separate sequence began several weeks later near Palu where an M w 7.5 event occurred that triggered a tsunami. In this study, we present hypocentre relocations for both earthquake sequences as well as all other regional earthquakes in eastern Indonesia. The relocations were performed using a teleseismic double-difference relocation method and arrival times for P and S waves from stations at local, regional, and teleseismic distances. The catalogue and phase data were taken from the Agency for Meteorology, Climatology and Geophysics (BMKG) of Indonesia and the International Seismological Centre (ISC) for the period of April 2009 through November 2018. The relocated catalogue provides an improved view of seismicity in eastern Indonesia over the study period, sharpening locations and interpretations of seismogenic features throughout the region. In the Lombok area, the relocated earthquakes clearly show a backarc thrust to the north of the Sunda-Banda Arc transition zone. The relocated aftershocks show that the destructive M w 7.0 and M w 6.9 earthquakes of the Lombok sequence ruptured two different regions: The M w 7.0 earthquake propagated westward, whereas the M w 6.9 earthquake propagated eastward. The entire sequence of Lombok earthquakes was most likely started by the M w 6.4 event as the initial event or foreshock, which then triggered backarc thrusts on both sides. Several weeks later and far to the northeast, the M w 7.5 Palu earthquake occurred along the Palu-Koro Fault, filling a seismic gap that had not ruptured in an M w 6.0 event or larger since at least 1900. The distribution of aftershocks indicates that the northern part of the Palu-Koro Fault has lower relative seismicity rates than the southern part at shallow depths, and that off fault aftershocks are mostly located to the east of the Palu-Koro Fault.

Lombok, Palu↗

USGS2016

Late Pleistocene and Holocene tephrostratigraphy of interior Alaska and Yukon: Key beds and chronologies over the past 30,000 years

The Aleutian Arc-Alaska Peninsula and Wrangell volcanic field are the main source areas for tephra deposits found across Alaska and northern Canada, and increasingly, tephra from these eruptions have been found further afield in North America, Greenland, and Europe. However, there have been no broad scale reviews of the Late Pleistocene and Holocene tephrostratigraphy for this region since the 1980s, and this lack of data is hindering progress in identifying these tephra both locally and regionally. To address this gap and the variable quality of associated geochemical and chronological data, we undertake a detailed review of the latest Pleistocene to Holocene tephra found in interior Alaska and Yukon. This paper discusses nineteen tephra that have distributions beyond southwest Alaska and that have the potential to become, or already are, important regional markers. This includes three ‘modern’ events from the 20th century, ten with limited data availability but potentially broad distributions, and six that are widely reported in interior Alaska and Yukon. Each tephra is assessed in terms of chronology, geochemistry and distribution, with new Bayesian age estimates and geochemical data when possible. This includes new major-element geochemical data for Crater Peak 1992, Redoubt 1989–90, and two andesitic tephra from St Michael Island (Tephra D), as well as revised age estimates for Dawson tephra, Oshetna, Hayes set H, Aniakchak CFE II, and the White River Ashes, northern and eastern lobes.

Quaternary Science Reviews↗

USGS1976

Structure and evolution of Bering Sea shelf south of St. Lawrence Island

The virtually featureless Beringian shelf south of St. Lawrence Island is underlain structurally by at least 14 basins. Encompassing a total area of more than 300,000 sq km, most of the basins are either elongate structural sags, grabens, or half (asymmetric) grabens beneath the outer shelf. The regional trend of these basins is northwest, parallel with that of the continental margin. Two of the basins, St. George and Navarin, contain 7 to 10 km of Upper Cretaceous(?) and Cenozoic sedimentary strata. A major divergence in dip of beds in the upper half of the sedimentary section may reflect an abrupt shelf-wide change in the rate of sedimentation and/or subsidence, probably during the Miocene. The outer sub-shelf basement grabens and adjacent ridges (horsts) are bounded by high-angle normal faults that exhibit growth-type structure. St. Matthew basin, an elongate, southwest-trending feature of the inner shelf, lies along the offshore expression of the Kaltag fault of western Alaska. The Kaltag fault, like the Denali fault in southwestern Alaska, does not extend to the outer Bering Sea shelf but ends or turns parallel with the margin within the inner shelf. The inner shelf is underlain by a broad basement high, Nunivak arch, the seaward half of which is characterized by an arcuate belt of high-frequency and high-amplitude magnetic anomalies. This zone of intense magnetic anomalies along the shelf is probably the signature of a Mesozoic magmatic arc that extends from southwestern Alaska to eastern Siberia and consists of Jurassic to Cretaceous plutonic and volcanic rocks. We speculate that this magmatic arc resulted from oblique convergence and subduction in the Mesozoic between the Kula(?) and North American plates along the eastern Beringian margin. Folding and uplift in the area of the present outer shelf occurred contemporaneously with magmatism along the inner shelf. Plate convergence apparently ceased by the end of the Mesozoic or t e beginning of the Cenozoic. Subsequently, the foldbelt underlying the outer shelf was eroded extensively and rifted extensionally to form large, deep basins. On the average, the shelf has subsided more than 1.5 km. Subsidence and sediment burial of the eroded orogen formed the modern Beringian shelf.

AAPG Bulletin↗

USGS1990

Remagnetization and northward translation of Mesozoic red chert from Cedros Island and the San Benito Islands, Baja California, Mexico

Samples for paleomagnetic analysis were collected from red radiolarian ribbon chert in a Franciscan-like subduction complex (Western Baja terrane) exposed along the western margin of the Baja California Peninsula. A 40-m-thick section of chert was sampled on Cedros Island, and a 30-m-thick and two smaller sections of chert were sampled on the San Benito Islands to the west. A site in pillow basalt underlying the chert also was sampled on Cedros Island. The sections of chert on Cedros Island and the San Benito Islands contain radiolaria ranging in age from Late Triassic to Early Cretaceous. All of these rocks have similar normal-polarity direction of magnetization, indicating that they were remagnetized long after deposition. Results from a chert site, including an intrastratal fold, also indicate that the magnetization is postdepositional. A significantly improved grouping (95% confidence level) of directions after correction for the structural attitudes of the Cedros and San Benito chert sections, however, implies that the remagnetization predates breaking up and incorporation of the chert into the subduction complex. Studies of modern subduction zones imply that the attitude of the ancient subducting slab, including the chert sections, was near horizontal (dip angles <10° at the time of remagnetization. Thus, assuming paleohorizontality, a paleolatitude of 12° ± 5° N can be estimated for the Western Baja terrane in mid-Cretaceous time. The paleomagnetic directions also indicate a subsequent poleward translation of 25° ± 7° in latitude (2,800 km) and a clockwise rotation of 56° ± 7° of the Western Baja terrane with respect to North America. The paleolatitude error limits at the 95% confidence level represent minimum values, because deviations of the bedding planes from horizontal during remagnetization would contribute to the error. A 10° NE dip of the subducting slab, however, would account for only 4° of the paleolatitude anomaly, and a ≃60° NE dip would be needed to account for the entire anomaly. Modern analogs, in combination with plate-reconstruction models, imply that the northward translation of the Western Baja terrane along the ancient convergent margin of North America could have been accomplished by arc-parallel strike-slip faulting that was driven by oblique subduction.

Baja California↗

USGS2012

Eruptive history of Mount Katmai, Alaska

Mount Katmai has long been recognized for its caldera collapse during the great pyroclastic eruption of 1912 (which vented 10 km away at Novarupta in the Valley of Ten Thousand Smokes), but little has previously been reported about the geology of the remote ice-clad stratovolcano itself. Over several seasons, we reconnoitered all parts of the edifice and sampled most of the lava flows exposed on its flanks and caldera rim. The precipitous inner walls of the 1912 caldera remain too unstable for systematic sampling; so we provide instead a photographic and interpretive record of the wall sequences exposed. In contrast to the several andesite-dacite stratovolcanoes nearby, products of Mount Katmai range from basalt to rhyolite. Before collapse in 1912, there were two overlapping cones with separate vent complexes and craters; their products are here divided into eight sequences of lava flows, agglutinates, and phreatomagmatic ejecta. Latest Pleistocene and Holocene eruptive units include rhyodacite and rhyolite lava flows along the south rim; a major 22.8-ka rhyolitic plinian fall and ignimbrite deposit; a dacite-andesite zoned scoria fall; a thick sheet of dacite agglutinate that filled a paleocrater and draped the west side of the edifice; unglaciated leveed dacite lava flows on the southeast slope; and the Horseshoe Island dacite dome that extruded on the caldera floor after collapse. Pre-collapse volume of the glaciated Katmai edifice was &sim;30 km 3 , and eruptive volume is estimated to have been 57±13 km 3 . The latter figure includes &sim;40±6 km 3 for the edifice, 5±2 km 3 for off-edifice dacite pyroclastic deposits, and 12±5 km 3 for the 22.8-ka rhyolitic pyroclastic deposits. To these can be added 13.5 km 3 of magma that erupted at Novarupta in 1912, all or much of which is inferred to have been withdrawn from beneath Mount Katmai. The oldest part of the edifice exposed is a basaltic cone, which gave a 40 Ar/ 39 Ar plateau age of 89 ± 25 ka. The seismic record of caldera collapse includes 14 earthquakes of magnitude 6.0–7.0. By combining the times of earthquakes, the hours of downwind plinian-fall episodes from Novarupta, and the stratigraphic record of hydrothermal explosion breccia and phreatic mud layers ejected around the caldera rim and intercalated within the Novarupta pumice-fall sequence, it can be inferred that collapse began in the 11th hour of the 60-h-long eruption and continued fitfully for 3.5 days. Several big landslides and pumiceous debris flows shaken loose by the collapse-related seismicity are bracketed in time by their levels of intercalation within the Novarupta pumice-fall sequence. An intracaldera lake was &sim;10 m deep by 1916, drained away in 1923, and has since deepened progressively to &sim;250 m today. Compositionally, products of Mount Katmai represent an ordinary medium-K arc array, both tholeiitic and calcalkaline, that extends from 51.6% to 72.3% SiO 2 . Values of 87 Sr/ 86 Sr range from 0.70335 to 0.70372, correlating loosely with fractionation indices. The 5–6 km 3 of continuously zoned andesite-dacite magma (58%–68% SiO 2 ) that erupted at Novarupta in 1912 was withdrawn from beneath Mount Katmai and bears close compositional affinity with products of that edifice, not with pre-1912 products of the adjacent Trident cluster. Evidence is presented that the 7–8 km 3 of high-silica rhyolite (77% SiO 2 ) released in 1912 is unlikely to have been stored under Novarupta or Trident. Pre-eruptive contiguity with the andesite-dacite reservoir is suggested by (1) eruption of &sim;3 km 3 of rhyolite magma first, followed by mutual mingling in fluctuating proportions; (2) thermal and redox continuity of the whole zoned sequence despite the wide compositional gap; (3) Nd, Sr, O isotopic, and rare earth element (REE) affinities of the whole array; (4) compositional continuity of the nearly aphyric rhyolite with the glass (melt) phase of the phenocryst-rich dacite; and (5) phase-equilibrium experiments that indicate similar shallow pre-eruptive storage depths (3–6 km) for rhyolite, dacite, and andesite.

Alaska↗

USGS2013

Intermediate‐depth intraslab earthquakes and arc volcanism as physical expressions of crustal and uppermost mantle metamorphism in subducting slabs

We elaborate on the well-known spatial association between axc volcanoes and Wadati Benioff zones and explore in detail their genetic relationships as dual physical expressions of slab metamorphism of the oceanic crust and uppermost mantle. At hypocentral depths less than 200 km intra slab Wadati-Benioff earthquakes tend to occur near the top surfaces of slabs. Subduction of very young lithosphere (age < 15-25 Ma) with high heat flow (> 75 mW/m 2) produces mainly shallow earthquakes and spaxse or absent arc volcanism. Subduction of older crust with normal heat flow (50-65 mW/m 2) produces markedly deeper intraslab earthquakes and generally normal volcanic vigor. Seismological observations show that the low-seismic-velocity gabbroic mineralogy of the crust may persist to depths of as much as 150 km in old, cold lithosphere but only to depths of 50-60 km in young, warm slabs. Metamorphic processes in the crust and shallow upper mantle of subducting slabs and the reactivation of faults originally created at shallow depths in the ocean basins probably control the occurrence of intraslab earthquakes to depths of as much as 350 kin. A conceptual model for this metamorphism incorporates the likely effects of water liberated by dehydration. Such dehydration facilitates both brittle faulting by fault reactivation and promotes the kinetics of the transformation of the anhydrous gabbro component of the crust to eclogite. Finite-element modelling shows that densification to eclogite is expected to produce extensional stresses in transformed crust and a smaller compression in the underlying mantle. This model helps explain why most intermediate-depth intraslab earthquakes occur just below the top surfaces of slabs and why many have focal mechanisms indicating down-dip extension. Young, warm slabs have mostly shallow intraslab earthquakes and sparse axc volcanoes because dehydration and eclogite formation largely cease before such slabs axe in contact with asthenosphere. These processes are evidently delayed by kinetic hindrance and the high pressure stability of hydrous phazes at low temperatures in older, colder subducting crust, and thus earthquake activity and asthenospheric-wedge melting tend to be focused at depths of 100-170 kin. Anomalous behavior correlated with the subduction of island-and seamount chains appears to be associated with anomalou shallow intraplate faulting and with perturbations of slab metamorphism by these chains.

Geophysical Monograph↗