[1] The HiRISE camera features a 0.5 m diameter primary mirror, 12 m effective focal length, and a focal plane system that can acquire images containing up to 28 Gb (gigabits) of data in as little as 6 seconds. HiRISE will provide detailed images (0.25 to 1.3 m/pixel) covering ∼1% of the Martian surface during the 2-year Primary Science Phase (PSP) beginning November 2006. Most images will include color data covering 20% of the potential field of view. A top priority is to acquire ∼1000 stereo pairs and apply precision geometric corrections to enable topographic measurements to better than 25 cm vertical precision. We expect to return more than 12 Tb of HiRISE data during the 2-year PSP, and use pixel binning, conversion from 14 to 8 bit values, and a lossless compression system to increase coverage. HiRISE images are acquired via 14 CCD detectors, each with 2 output channels, and with multiple choices for pixel binning and number of Time Delay and Integration lines. HiRISE will support Mars exploration by locating and characterizing past, present, and future landing sites, unsuccessful landing sites, and past and potentially future rover traverses. We will investigate cratering, volcanism, tectonism, hydrology, sedimentary processes, stratigraphy, aeolian processes, mass wasting, landscape evolution, seasonal processes, climate change, spectrophotometry, glacial and periglacial processes, polar geology, and regolith properties. An Internet Web site (HiWeb) will enable anyone in the world to suggest HiRISE targets on Mars and to easily locate, view, and download HiRISE data products.

/pdf/mars-reconnaissance-orbiter-s-high-resolution-imaging-4bjw0ks5y9.pdf

Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE)

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scanner on NASA's Earth Observing System (EOS)-AM1 satellite (launch scheduled for 1998) will collect five bands of thermal infrared (TIR) data with a noise equivalent temperature difference (NE/spl Delta/T) of /spl les/0.3 K to estimate surface temperatures and emissivity spectra, especially over land, where emissivities are not known in advance. Temperature/emissivity separation (TES) is difficult because there are five measurements but six unknowns. Various approaches have been used to constrain the extra degree of freedom. ASTER's TES algorithm hybridizes three established algorithms, first estimating the normalized emissivities and then calculating emissivity band ratios. An empirical relationship predicts the minimum emissivity from the spectral contrast of the ratioed values, permitting recovery of the emissivity spectrum. TES uses an iterative approach to remove reflected sky irradiance. Based on numerical simulation, TES should be able to recover temperatures within about /spl plusmn/1.5 K and emissivities within about /spl plusmn/0.015. Validation using airborne simulator images taken over playas and ponds in central Nevada demonstrates that, with proper atmospheric compensation, it is possible to meet the theoretical expectations. The main sources of uncertainty in the output temperature and emissivity images are the empirical relationship between emissivity values and spectral contrast, compensation for reflected sky irradiance, and ASTER's precision, calibration, and atmospheric compensation.

A temperature and emissivity separation algorithm for Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images

Large igneous provinces and mass extinctions

Volcanism in Iceland in historical time: Volcano types, eruption styles and eruptive history

Diverse subsidence geometries and collapse processes for ash-flow calderas are inferred to reflect varying sizes, roof geometries, and depths of the source magma chambers, in combination with prior volcanic and regional tectonic influences. Based largely on a review of features at eroded pre-Quaternary calderas, a continuum of geometries and subsidence styles is inferred to exist, in both island-arc and continental settings, between small funnel calderas and larger plate (piston) subsidences bounded by arcuate faults. Within most ring-fault calderas, the subsided block is variably disrupted, due to differential movement during ash-flow eruptions and postcollapse magmatism, but highly chaotic piecemeal subsidence appears to be uncommon for large-diameter calderas. Small-scale downsag structures and accompanying extensional fractures develop along margins of most calderas during early stages of subsidence, but downsag is dominant only at calderas that have not subsided deeply. Calderas that are loci for multicyclic ash-flow eruption and subsidence cycles have the most complex internal structures. Large calderas have flared inner topographic walls due to landsliding of unstable slopes, and the resulting slide debris can constitute large proportions of caldera fill. Because the slide debris is concentrated near caldera walls, models from geophysical data can suggest a funnel geometry, even for large plate-subsidence calderas bounded by ring faults. Simple geometric models indicate that many large calderas have subsided 3–5 km, greater than the depth of most naturally exposed sections of intracaldera deposits. Many ring-fault plate-subsidence calderas and intrusive ring complexes have been recognized in the western U.S., Japan, and elsewhere, but no well-documented examples of exposed eroded calderas have large-scale funnel geometry or chaotically disrupted caldera floors. Reported ignimbrite "shields" in the central Andes, where large-volume ash-flows are inferred to have erupted without caldera collapse, seem alternatively interpretable as more conventional calderas that were filled to overflow by younger lavas and tuffs. Some exposed subcaldera intrusions provide insights concerning subsidence processes, but such intrusions may continue to evolve in volume, roof geometry, depth, and composition after formation of associated calderas.

Subsidence of ash-flow calderas: Relation to caldera size and magma-chamber geometry

Inflated pahoehoe sheet flows have a distinctive horizontal upper surface, which can be several hundred meters across, and are bounded by steep monoclinal uplifts. The inflated sheet flows we studied ranged from 1 to 5 m in thickness, but initially propagated as thin sheets of fluid pahoehoe lava, generally 20-30 cm thick. Individual lobes originated at outbreaks from the inflated front of a prior sheet-flow lobe and initially moved rapidly away from their source. Velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow. As the outward flow velocity decreases, cooling promotes rapid crustal growth. At first, the crust behaves plastically as pahoehoe toes form. After the crust attains a thickness of 2-5 cm, it behaves more rigidly and develops enough strength to retain incoming lava, thus increasing the hydrostatic head at the flow front. The increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow, resulting in uniform uplift of the entire sheet-flow lobe. Initial uplift rates are rapid (flows thicken to 1 m in 1-2 hours), but rates decline sharply as crustal thickness increases, and as outbreaks occur from the margins of the inflating lobe. One flow reached a final thickness of nearly 4 m after 350 hr. Inflation data define power-law curves, whereas crustal cooling follows square root of time relationships; the combination of data can be used to construct simple models of inflated sheet flows.

As the flow advances, preferred pathways develop in the older portions of the liquid-cored flow; these pathways can evolve into lavatube systems within a few weeks. Formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1-2 orders of magnitude slower. If advance of the sheet flow is terminated, the tube remains filled with lava that crystallizes in situ rather than draining to form the cave-like lava tubes commonly associated with pahoehoe flows.

Inflated sheet flows from Kilauea and Mauna Loa are morphologically similar to some thick Icelandic and submarine sheet flows, suggesting a similar mechanism of emplacement. The planar, sheet-like geometry of flood-basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava.

Emplacement and inflation of pahoehoe sheet flows: observations and measurements of active lava flows on Kilauea volcano, Hawaii

Extensive flows of the Columbia River Basalt (CRB) Group in Washington, Oregon, and Idaho are dominantly inflated compound pahoehoe sheet lavas. Early studies recognized that CRB lavas are compound pahoehoe flows, with textures suggesting low flow velocities, but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks. However, small volume (< 1 km³) compound pahoehoe flows on Kilauea, Hawai'i, demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger (10–20 km3) pahoehoe flows in Iceland. The vertical distribution of vesicles and other morphologic features within CRB lava flows indicate that they grew similarly by inflation. Small pahoehoe lobes at the base and top of many CRB pahoehoe lava flows indicate emplacement in a gradual, piecemeal manner rather than as a single flood. We propose that each thick CRB sheet flow was active for months to years and that each group of flows produced by a single eruption (a flow field) was emplaced slowly over many years.

A new model for the emplacement of Columbia River basalts as large, inflated Pahoehoe Lava Flow Fields

From 1986 to 1997, the Pu'u 'O'o-Kupaianaha eruption of Kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10–12 km from vents on the volcano's east rift zone to the ocean. Within a kilometer of the vent, tubes were as much as 20 m high and 10–25 m wide. On steep slopes (4–10°) a little farther away from the vent, some tubes formed by roofing over of lava channels. Lava streams were typically 1–2 m deep flowing within a tube that here was typically 5 m high and 3 m wide. On the coastal plain (<1°), tubes within inflated sheet flows were completely filled, typically 1–2 m high, and several tens of meters wide. Tubes develop as a flow's crust grows on the top, bottom, and sides of the tubes, restricting the size of the fluid core. The tubes start out with nearly elliptical cross-sectional shapes, many times wider than high. Broad, flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts. Temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting. Sometimes, the tubes began downcutting. Progressive downcutting was frequently observed through skylights; a rate of 10 cm/d was measured at one skylight for nearly 2 months.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/97JB03576

Observations on basaltic lava streams in tubes from Kilauea Volcano, island of Hawai'i

The 1990 Kalapana flow field is a complex patchwork of tube-fed pahoehoe flows erupted from the Kupaianaha vent at a low effusion rate (approximately 3.5 m3/s). These flows accumulated over an 11-month period on the coastal plain of Kilauea Volcano, where the pre-eruption slope angle was less than 2°. the composite field thickened by the addition of new flows to its surface, as well as by inflation of these flows and flows emplaced earlier. Two major flow types were identified during the development of the flow field: large primary flows and smaller breakouts that extruded from inflated primary flows. Primary flows advanced more quickly and covered new land at a much higher rate than breakouts. The cumulative area covered by breakouts exceeded that of primary flows, although breakouts frequently covered areas already buried by recent flows. Lava tubes established within primary flows were longer-lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply; tubes within breakouts were never reoccupied once the supply was interrupted. During intervals of steady supply from the vent, the daily areal coverage by lava in Kalapana was constant, whereas the forward advance of the flows was sporadic. This implies that planimetric area, rather than flow length, provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes.

Development of the 1990 Kalapana flow field, Kilauea Volcano, Hawaii

INTRODUCTION Fissures sliced through Kīlauea Volcano’s lower east rift zone on 3 May 2018, eventually engulfing hundreds of structures in lava flows and triggering a collapse at the summit. During the eruption, we employed a rapid routine for geochemical analysis of lava, developed over 6 years of monitoring the prior continuous eruption at Kīlauea. The application of this routine elevated lava chemistry to a near real-time data stream in eruption monitoring, similar to seismic and geodetic data. It provided an unparalleled opportunity to understand changes in magma characteristics during a rapidly evolving eruptive crisis. RATIONALE Lava chemistry provides vital information on the underground sources of magma, eruptive conditions, temperature, and physical properties of lava flows. However, analytical techniques are typically slow, leaving chemical analysis of lava as a retrospective tool in the volcano sciences. We developed an analytical procedure to characterize the geochemistry of lava within a few hours of sample collection, allowing us to identify a specific suite of major and trace elements that track lava compositions and estimate lava temperatures through chemical geothermometers. This information was used to inform response teams of shifts in eruptive conditions. RESULTS The initial fissures erupted low volumes of chemically evolved basaltic lavas from 3 to 9 May, which were viscous and cool (~1110°C). On 13 May we detected less-evolved compositions and an increase in inferred lava temperatures (~1130°C). We informed science and response teams that the arrival of more fluid and voluminous lava was likely. Beginning 17 to 18 May, the lava from the primary fissures became increasingly less chemically evolved, hotter, and more fluid. By 28 May, activity focused on a single vent (fissure 8). This vent fed a massive outpouring of hotter (~1145°C) lava that continued for more than 2 months. During this stage, lavas became slightly hotter and lost the cargo of lower-temperature minerals that were initially abundant. The lava carried olivine crystals with unusually high MgO, indicative of the presence of much hotter magma (>1270°C) somewhere in the plumbing system. A second dominant olivine population formed in cooler magma similar to what was being erupted previously at the summit lava lake. We also identified simultaneous, but more explosive, repetitive outbursts of andesite lava. This highly viscous and evolved composition, not previously known from Kīlauea, erupted at low temperatures (1060° to 1090°C) on a fissure offset from the other eruption fissures. The chemical and mineralogical fingerprint of this lava was also detected at other fissures several kilometers from the andesite vent. CONCLUSION Analysis of the data during the eruption revealed that at least three different sources of magma were feeding the eruption. The first two were the chemically evolved basalt of the initial fissures and the highly viscous andesite. Both are volumetrically minor sources that represent distinct pockets of old residual magma from Kīlauea’s east rift zone that evolved for more than 55 years, cooling and crystallizing at depth. The third and volumetrically more substantial source was less-evolved and hotter basalt of fissure 8. This source was similar in composition to the magma erupted at Kīlauea in the years before 2018 and was ultimately derived from the summit region. Draining and collapse of the summit by this voluminous eruption may have stirred up deeper, hotter parts of the summit magma system and sent mixed magma down the rift. By the final 20 days of the eruption, most magma stored within the active rift system had flushed out. Posteruption analyses done by traditional geochemical methods confirmed that the rapid-response routine produced comparable data and validated the models proposed during the active eruption. Our work has demonstrated that geochemical analyses of lava samples in near-real-time can yield critical information that enhances hazard assessments and risk mitigation during an eruption.

https://science.sciencemag.org/content/sci/366/6470/eaaz0147.full.pdf

Ken Hon

Papers

Emplacement and inflation of pahoehoe sheet flows: observations and measurements of active lava flows on Kilauea volcano, Hawaii

A new model for the emplacement of Columbia River basalts as large, inflated Pahoehoe Lava Flow Fields

Observations on basaltic lava streams in tubes from Kilauea Volcano, island of Hawai'i

Development of the 1990 Kalapana flow field, Kilauea Volcano, Hawaii

The tangled tale of Kīlauea's 2018 eruption as told by geochemical monitoring.