Ice-confined construction of a large basaltic volcano—Austurfjöll massif, Askja, Iceland

Austurfjöll is the largest basaltic glaciovolcanic massif at Askja volcano (Central Iceland), and through detailed studies of its volcanological and geochemical characteristics, we provide a detailed account of the sequence and structure of the ice-confined construction of a large Icelandic basaltic volcano. In particular, Austurfjöll represents a geometry of vents, and resulting glaciovolcanic morphology, not previously documented in ice-confined basaltic volcanoes. Austurfjöll was constructed during two major phases of basaltic volcanism, via seven eruptive episodes through disperse fissure-dominated eruptions. The earliest episode involved a rare and poorly exposed example of subaerial activity, and this was succeeded by six episodes involving the eruption of ice-confined pillow lavas and numerous overlapping fissure eruptions of phreatomagmatic tephra. Evidence of local subaerial lavas and tephras indicates the local growth of eruptive centers above englacial lake levels, and subsequent flooding, but no prolonged subaerial activity. Localized ice-contact facies, paleowater levels, and diamictons indicate the position and thickness of the ice was variable during the construction of Austurfjöll, and eruptive activity likely occurred in multiple and variable level meltwater lakes during the last glacial period. Lithofacies evidence including gradational transitions from effusive to explosive deposits, superposition of fragmental facies above coherent facies, and drainage channels suggest that changes in eruptive style were driven largely by external factors such as drainage and the increasing elevation of the massif. This study emphasizes the unique character of Austurfjöll, being composed of large pillow lava sheets, numerous (> 40) overlapping glaciovolcanic tindars, and only localized emergent deposits, as a product of its prolonged ice-confined eruptive history, contrasts with previous descriptions of tuyas and tindars

Foundation Evaluation with Micro Intrusive Testing Foundation Evaluation With Micro Intrusive Testing 5. Report Date 6. Performing Organization Code 7. Authors 13. Type of Report and Period Covered

Abstract This research developed new abrasive-waterjet equipment and techniques for drilling small holes, approximately 3/8-inch in diameter, in reinforced concrete. The ultimate goal is to evaluate bridge foundations and abutments to determine the susceptibility of the structure to failure if scour occurs. The overall research effort consists of three phases: 1) equipment development and laboratory testing, 2) large-scale field tests, and 3) implementation on existing bridges to evaluate foundations and abutments. The current research and final report were for Phase I of this project -equipment development and laboratory testing. The abrasive-waterjet drill developed during this research has three major components: 1) a 5000 pounds per square inch (psi) pump, 2) an accumulator cart, and 3) a drill stand. The pump is an off-the-shelf contractor-grade pressure washer. The pump accelerates water and an abrasive past a critical velocity at the drill tip so that the abrasive water stream will readily erode the target material. The diameter of the drill rod and tip were reduced in this research from typical diameters of greater than one inch, to as small as 1/8 of an inch. Laboratory tests focused on abrasive-waterjet drilling of a variety of materials, including red brick, concrete masonry units, high-strength reinforced concrete, steel rebar, Pottsville sandstone, a telephone pole, a steel oil well casing and 3/4-inch thick glass plate. Drill rod and tip diameters used in these tests ranged between 1/8 and 9/16-inch. Operating at 5,000-psi with a water flow rate of approximately two gallons/minute, the garnet feed rate was between 1.3 and 6 pounds/minute. Within these operating ranges the abrasive-waterjet drill consistently produced holes between 3/8 and ½ inch to depths between two and 36 inches. The laboratory results showed that this new abrasive-waterjet drill is capable of drilling a small diameter hole, approximately 3/8 of an inch, through typical civil engineering materials. The drill produced straight, in-gauge holes up to 16 inches deep. After a thorough literature review, the authors are confident that this is the smallest diameter waterjet application to date for geological or geotechnical drilling

Remote sensing and geologic mapping of glaciovolcanic deposits in the region surrounding Askja (Dyngjufjöll) volcano, Iceland

The surface geology of the Northern Volcanic Zone in Iceland is dominated by volcanic ridges, central volcanoes, shield volcanoes, and tuyas. The largest features are typically ice-confined (glaciovolcanic) in origin, and are overlain by voluminous Holocene (subaerial) lavas and glacial outwash deposits. The literature has focused heavily on prominent or very young features, neglecting small and older volcanic features. The purpose of this study is to demonstrate the application of remote-sensing mapping techniques to the glaciovolcanic environment in order to identify dominant lithologies and determine locations for textural, stratigraphic, and age studies. The deposits targeted in this study occur on and around Askja volcano, in central Iceland, including Pleistocene glaciovolcanic tuffs and subaerial pumice from the 1875 rhyolitic eruption of Askja. Data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were used in conjunction with previously published geologic and remote-sensing data sets and recent field work on glaciovolcanic deposits of Askja for validation. Remotely acquired data sets include aerial photographs and one ASTER scene obtained in August 2010. Visible and near-infrared (VNIR) and thermal infrared (TIR) classifications and linear deconvolution of the TIR emissivity data were performed using end-members derived from regions of interest and laboratory spectra. End-members were selected from samples of representative lithologic units within the field area, including glaciovolcanic deposits (pillow lavas, tuffs, etc.), historical deposits (1875 pumice, 1920s basaltic lavas), and Holocene basaltic lavas from Askja. The results demonstrate the potential for remote sensing-based ground cover mapping of areas of glaciovolcanic deposits relevant to palaeo-ice reconstructions in areas such as Iceland, Antarctica, and British Columbia. Remote sensing-based mapping will benefit glaciovolcanic studies, by determining the lithologic variability of these relatively inaccessible massifs and serving as an important springboard for the identification of future field sites in remote areas