ALBERT

Description: Dedicated scientific measurements of the strength and direction of the Earth's magnetic field began at Greenwich and Kew observatories in London, UK, in the middle of the 19th century. Using advanced techniques for the time, light-sensitive photographic paper and light-levered reflections from magnetized needles, allowed continuous analogue magnetograms to be recorded. By good fortune, both observatories (which were located around 20 km apart) were in full operation around the so-called Carrington storm in the early September 1859 and the precursor storm in late August, providing as complete a record as possible. Based on digital images of the magnetograms and information from the observatory yearbooks and subsequent scientific papers, we extract and scale the measurements to SI units, allowing us to extract minute cadence values. The magnetogram records have several missing periods, lost as the traces moved off-page due to the magnitude of the storm. We present the most complete digitized magnetic records to date of the ten-day period from 25th August to 5th September 1859 encompassing the Carrington storm and its lesser recognized precursor which may have been just as large. We discuss some of the issues encountered in deciphering the old records and methods for cross checking and validating the output values.

Description: To understand the mechanism that induces repetitive explosive eruptions from lava ponds, we investigated the architecture of the ‘plug’ at the top of a volcanic conduit from the proximal deposits and vent wall outcrops of the 2018 activity at Shinmoedake volcano, Japan. Most deposits were angular with red surfaces, sometimes with red tuffisite veins. Some blocks with black and deformed tuffisite veins were present. The walls of the 2018 vent in the summit crater were composed of red angular blocks and ash. Density and tensile strength measurements indicated a higher density and tensile strength for black tuffisite-bearing blocks than those for red tuffisite-bearing blocks and red surface blocks. The surface color of red materials originated from fine Fe oxide(s) on pyroxene microlites, indicating they were formed by the oxidation at high fO2 after fracturing. These results indicate that the plug architecture consists of a fragile and permeable upper plug through which atmospheric air circulates, and a dense and tough lower plug due to ductile deformation. Within this framework, repetitive explosive eruptions are explained by the following model: (1) fracturing of a dense plug due to an explosion, (2) healing of fractures by ductile deformation in the lower plug, which inhibits the gas supply from beneath it whilst air penetrates the upper plug and oxidizes the fragments (3) explosion of the lower plug due to the overpressure of accumulated gas. These new findings contribute to understanding the mechanisms of intermittent explosions and degassing in lava ponds.