Rootless shield and perched lava pond collapses at Kīlauea Volcano,Hawai'i

Effusion rate is a primary measurement used to judge the expected advance rate, length, and hazard potential of lava flows. At basaltic volcanoes, the rapid draining of lava stored in rootless shields and perched ponds can produce lava flows with much higher local effusion rates and advance velocities than would be expected based on the effusion rate at the vent. For several months in 2007–2008, lava stored in a series of perched ponds and rootless shields on Kīlauea Volcano, Hawai'i, was released episodically to produce fast-moving 'a'ā lava flows. Several of these lava flows approached Royal Gardens subdivision and threatened the safety of remaining residents. Using time-lapse image measurements, we show that the initial time-averaged discharge rate for one collapse-triggered lava flow was approximately eight times greater than the effusion rate at the vent. Though short-lived, the collapse-triggered 'a'ā lava flows had average advance rates approximately 45 times greater than that of the pāhoehoe flow field from which they were sourced. The high advance rates of the collapse-triggered lava flows demonstrates that recognition of lava accumulating in ponds and shields, which may be stored in a cryptic manner, is vital for accurately assessing short-term hazards at basaltic volcanoes.     

The Krafla fissure swarm, Iceland, and its formation by rifting events

Fissure swarms at divergent plate boundaries are activated in rifting events, during which intense fracturing occurs in the fissure swarm accompanied by intrusion of magma to form dikes that sometimes lead to eruptions. To study the evolution of fissure swarms and the behaviour of rifting events, detailed mapping was carried out on fractures and eruptive fissures within the Krafla fissure swarm (KFS). Fracture densities of dated lava flows ranging from 10,000?years bp to ~30?years old were studied, and the fracture pattern was compared with data on the historical Myvatn rifting episode (1724–1729) and the instrumentally recorded Krafla rifting episode (1975–1984). Additionally, the interaction of transform faults and fissure swarms was studied by analysing the influence of the Húsavík transform faults on the KFS. During the historical rifting episodes, eruptions on the fissure swarm occurred within ~7?km from the Krafla central volcano, although faults and fractures were formed or activated at up to 60–70?km distance. This is consistent with earlier rifting patterns, as Holocene eruptive fissures within the KFS are most common closer to the central volcano. Most fractures within the central Krafla caldera are parallel to the overall orientation of the fissure swarm. This suggests that the regional stress field is governing in the Krafla central volcano, while the local stress field of the volcano is generally weak. A sudden widening of the graben in the northern KFS and a local maximum of fracture density at the junction of the KFS and the extrapolation of the Húsavík transform fault zone indicates possible buried continuation of the Húsavík transform fault zone which extends to the KFS. Eruptive fissures are found farther away from the Krafla central volcano in the southern KFS than in the northern KFS. This is either due to an additional magma source in the southern KFS (the Heiearsporeur volcanic system) or caused by the Húsavík transform faults, transferring some of the plate extension in the northern part. Fracture density within particular lava flow fields increases with field age, indicating that repeated rifting events have occurred in the fissure swarm during the last 10,000?years bp. The fracture density in the KFS is also generally higher closer to the Krafla central volcano than at the ends of the fissure swarm. This suggests that rifting events are more common in the parts of the fissure swarm closer to the Krafla central volcano.     

Radiative transfer corrections for accurate spectroscopic measurements of volcanic gas emissions

There is widespread use of passive remote sensing techniques to quantify trace gas column densities in volcanic plumes utilizing scattered sunlight as a light source. Examples include passive DOAS, COSPEC, and the SO₂ camera. In order to calculate trace gas concentrations or volcanic emission fluxes, knowledge about the optical path through the plume is necessary. In the past, a straight photon path through the plume has always been assumed although it was known that this is not always true. Here we present the results of model studies conducted specifically to quantify the effects of realistic radiative transfer in and around volcanic plumes on ground-based remote sensing measurements of SO₂. The results show that measurements conducted without additional information on average photon paths can be inaccurate under certain conditions, with possible errors spanning more than an order of magnitude. Both over and underestimation of the true column density can occur. Actual errors depend on parameters such as distance between instrument and plume, plume SO₂ concentration, plume aerosol load, as well as aerosol conditions in the ambient atmosphere. As an example, a measurement conducted with an SO₂ camera is discussed, the results of which can only be correctly interpreted if realistic radiative transfer is considered. Finally, a method is presented which for the first time allows the retrieval of actual average photon paths in spectroscopic (i.e. DOAS) measurements of adequate resolution. By allowing for a wavelength dependent column density during the evaluation of DOAS measurements, we show how radiative transfer effects can be corrected using information inherently available in the measured spectra, thus greatly enhancing the accuracy of DOAS measurements of volcanic emissions.     

Turbidite stratigraphy in proglacial lakes: Deciphering trigger mechanisms using a statistical approach

Turbidites embedded in lacustrine sediment sequences are commonly used to reconstruct regional flood or earthquake histories. A critical step for this method to be successful is that turbidites and their trigger mechanisms are determined unambiguously. The latter is particularly challenging for prehistoric proglacial lake records in high-seismicity settings where both earthquake-generated and flood-generated turbidites interrupt the background varved sedimentation. This calls for a new method to allow efficient and objective identification and classification of turbidites. This study examined turbidites in five long (9 to 17 m) sediment cores from Eklutna Lake, a proglacial lake in south-central Alaska, using standard core logging and grain-size data. A novel statistical approach is presented, in which varve-thickness distributions were first analyzed to objectively identify the thickest turbidites and distinguish them from background sedimentation. For each turbidite, a selection of variables were then measured, including: basal grain-size, thickness, magnetic susceptibility and spectrophotometric variables. Triggering mechanisms were discriminated by a combination of principal component analysis and clustering, and by calibration with historical events. Using this approach, a 2250 year long lake-wide event stratigraphy was constructed, with 94 prehistoric events, including 24 earthquake and 70 flood events. Basal grain-size and thickness variables turn out to be the most effective proxies for discrimination. This statistical approach is a powerful and new method to identify turbidites and their triggering mechanisms in long prehistoric sediment records. It opens up new prospects for palaeoseismological, palaeohydrological and palaeoclimate studies in proglacial lakes worldwide.     

Are peatlands cool humid islands in a landscape?

This study proposed that due to their high standing water tables that peatlands would be cold humid islands within their landscape, and especially so relative to farmland on mineral soils. To test this hypothesis, we measured air temperature and humidity at 17 locations along a 7.8 km transect across the UK's largest lowland raised bog from February 2018 to January 2019. Air temperature and humidity were measured hourly for 1 year and supported with spot albedo measurements. The study represented a factorial experiment with respect to sites of measurement, the type of land use (peat vs. arable land) and time of sampling over both the seasonal and diurnal cycles. We show that: (a) That although mean annual temperature was not significantly different between arable and peatlands, the arable land showed a decreased amplitude to its seasonal cycle – this is the reverse of the expected pattern. (b) The albedo of the peatland was significantly lower than that of arable land showing that vegetated peatland still absorbed more solar radiation. (c) The specific humidity was lower on the peatland than on the surrounding arable land. The study showed that while shrubby vegetation exists over a peatland then energy budgets are more likely to be dominated by the lower aerodynamic resistance and lower albedo of the vegetated peatland relative to arable land. Thus, shrub-dominated peatlands will not be a cold humid island in their landscape.     

Theories on formation of an anomalous anticyclone in western North Pacific during El Niño: A review

The western North Pacific anomalous anticyclone (WNPAC) is an important atmospheric circulation system that conveys El Niño impact on East Asian climate. In this review paper, various theories on the formation and maintenance of the WNPAC, including warm pool atmosphere–ocean interaction, Indian Ocean capacitor, a combination mode that emphasizes nonlinear interaction between ENSO and annual cycle, moist enthalpy advection/Rossby wave modulation, and central Pacific SST forcing, are discussed. It is concluded that local atmosphere–ocean interaction and moist enthalpy advection/Rossby wave modulation mechanisms are essential for the initial development and maintenance of the WNPAC during El Niño mature winter and subsequent spring. The Indian Ocean capacitor mechanism does not contribute to the earlier development but helps maintain the WNPAC in El Niño decaying summer. The cold SST anomaly in the western North Pacific, although damped in the summer, also plays a role. An interbasin atmosphere–ocean interaction across the Indo-Pacific warm pool emerges as a new mechanism in summer. In addition, the central Pacific cold SST anomaly may induce the WNPAC during rapid El Niño decaying/La Niña developing or La Niña persisting summer. The near-annual periods predicted by the combination mode theory are hardly detected from observations and thus do not contribute to the formation of the WNPAC. The tropical Atlantic may have a capacitor effect similar to the tropical Indian Ocean.     

Assessing the vulnerability of food crop systems in Africa to climate change

Africa is thought to be the region most vulnerable to the impacts of climate variability and change. Agriculture plays a dominant role in supporting rural livelihoods and economic growth over most of Africa. Three aspects of the vulnerability of food crop systems to climate change in Africa are discussed: the assessment of the sensitivity of crops to variability in climate, the adaptive capacity of farmers, and the role of institutions in adapting to climate change. The magnitude of projected impacts of climate change on food crops in Africa varies widely among different studies. These differences arise from the variety of climate and crop models used, and the different techniques used to match the scale of climate model output to that needed by crop models. Most studies show a negative impact of climate change on crop productivity in Africa. Farmers have proved highly adaptable in the past to short- and long-term variations in climate and in their environment. Key to the ability of farmers to adapt to climate variability and change will be access to relevant knowledge and information. It is important that governments put in place institutional and macro-economic conditions that support and facilitate adaptation and resilience to climate change at local, national and transnational level.     

Reappraising the P–T evolution of the Rogaland–Vest Agder Sector,southwestern Norway

The Rogaland-Vest Agder Sector of southwestern Norway comprises high-grade metamorphic rocks intruded by voluminous plutonic bodies that include the ~1000 km~2 Rogaland Igneous Complex(RIC).New petrographic observations and thermodynamic phase equilibria modelling of three metapelitic samples collected at various distances(30 km,10 km and ~ 10 m) from one of the main bodies of RIC anorthosite were undertaken to assess two alternative P-T-t models for the metamorphic evolution of the area.The results are consistent with a revised two-phase evolution.Regional metamorphism followed a clockwise P-T path reaching peak conditions of ~ 850-950 ℃ and ~7-8 kbar at ~1035 Ma followed by high-temperature decompression to ~5 kbar at ~950 Ma,and resulted in extensive anatexis and melt loss to produce highly residual rocks.Subsequent emplacement of the RIC at ~930 Ma caused regional-scale contact metamorphism that affected country rocks 10 km or more from their contact with the anorthosite.This thermal overprint is expressed in the sample proximal to the anorthosite by replacement of sillimanite by coarse intergrowths of cordierite plus spinel and growth of a second generation of garnet,and in the intermediate(10 km) sample by replacement of sapphirine by coarse intergrowths of cordierite,spinel and biotite.The formation of late biotite in the intermediate sample may suggest the rocks retained small quantities of melt produced by regional metamorphism and remained at temperatures above the solidus for up to 100 Ma.Our results are more consistent with an accretionary rather than a collisional model for the Sveconorwegian Orogen.     

Temporal observations of rip current circulation on a macro-tidal beach

A field experiment was conducted on a high energy macro-tidal beach (Perranporth, UK) to examine rip current dynamics over a low-tide transverse bar/rip system in response to changing tide and wave conditions. Hydrodynamic data were collected using an array of in situ acoustic doppler current meters and pressure transducers, as well as 12 GPS-tracked Lagrangian surf zone drifters. Inter-tidal and sub-tidal morphology were measured through RTK-GPS and echo-sounder surveys. Data were collected for eight consecutive days (15 tides) over a spring-neap tidal cycle with tidal ranges of 4–6.5 m and offshore significant wave heights of 1–2 m and peak periods of 5–12 s.