Using dissolved H₂O in rhyolitic glasses to estimate palaeo-ice thickness during a subglacial eruption at Bláhnúkur(Torfajökull, Iceland)

The last decade has seen the refinement of a technique for reconstructing palaeo-ice thicknesses based on using the retained H2O and CO2 content in glassy eruptive deposits to infer quenching pressures and therefore ice thicknesses. The method is here applied to Bláhnúkur, a subglacially erupted rhyolitic edifice in Iceland. A decrease in water content from ~0.7 wt.% at the base to ~0.3 wt.% at the top of the edifice suggests that the ice was 400 m thick at the time of the eruption. As Bláhnúkur rises 350 m above the surrounding terrain, this implies that the eruption occurred entirely within ice, which corroborates evidence obtained from earlier lithofacies studies. This paper presents the largest data set (40 samples) so far obtained for the retained volatile contents of deposits from a subglacial eruption. An important consequence is that it enables subtle but significant variations in water content to become evident. In particular, there are anomalous samples which are either water-rich (up to 1 wt.%) or water-poor (~0.2 wt.%), with the former being interpreted as forming intrusively within hyaloclastite and the latter representing batches of magma that were volatile-poor prior to eruption. The large data set also provides further insights into the strengths and weaknesses of using volatiles to infer palaeo-ice thicknesses and highlights many of the uncertainties involved. By using examples from Bláhnúkur, the quantitative use of this technique is evaluated. However, the relative pressure conditions which have shed light on Bláhnúkur’s eruption mechanisms and syn-eruptive glacier response show that, despite uncertainties in absolute values, the volatile approach can provide useful insight into the mechanisms of subglacial rhyolitic eruptions, which have never been observed

Controls on explosive-effusive volcanic eruption styles

One of the biggest challenges in volcanic hazard assessment is to understand how and why eruptive style changes within the same eruptive period or even from one eruption to the next at a given volcano. This review evaluates the competing processes that lead to explosive and effusive eruptions of silicic magmas. Eruptive style depends on a set of feedbacks involving interrelated magmatic properties and processes. Foremost of these are magma viscosity, gas loss, and external properties such as conduit geometry. Ultimately, these parameters control the speed at which magmas ascend, decompress and outgas en route to the surface, and thus determine eruptive style and evolution

Clinical evaluation of intraoperative near misses in laparoscopic rectal cancer surgery.

OBJECTIVE: To investigate the frequency, nature, and severity of intraoperative adverse near miss events within advanced laparoscopic surgery and report any associated clinical impact. BACKGROUND: Despite implementation of surgical safety initiatives, the intraoperative period is poorly documented with evidence of underreporting. Near miss analyses are undertaken in high-risk industries but not in surgical practice. METHODS: Case video and data from 2 laparoscopic total mesorectal excision randomized controlled trials were analyzed (ALaCaRT ACTRN12609000663257, 2D3D ISRCTN59485808). Intraoperative adverse events were identified and categorized using the observational clinical human reliability analysis technique. The EAES classification was applied by 2 blinded assessors. EAES grade 1 events (nonconsequential error, no damage, or need for correction) were considered near misses. Associated clinical impact was assessed with early morbidity and histopathology outcomes. RESULTS: One hundred seventy-five cases contained 1113 error events. Six hundred ninety-eight (62.7%) were near misses (median 3, IQR 2-5, range 0-15) with excellent inter-rater and test-retest reliability (κ=0.86, 95% CI 0.83-0.89, P < 0.001 and κ=0.88, 95% CI 0.85-0.9, P < 0.001 respectively). Significantly more near misses were seen in patients who developed early complications (4 (3-6) vs. 3 (2-4), P < 0.001). Higher numbers of near misses were seen in patients with more numerous (P = 0.002) and more serious early complications (P = 0.003). Cases containing major intraoperative adverse events contained significantly more near misses (5 (3-7) vs. 3 (2-5), P < 0.001) with a major event observed for every 19.4 near misses. CONCLUSION: Intraoperative adverse events and near misses can be reliably and objectively captured in advanced laparoscopic surgery. Near misses are commonplace and closely associated with morbidity outcomes