Assessing the Use of Optical Satellite Images to Detect Volcanic Impacts on Glacier Surface Morphology

Globally, about 250 Holocene volcanoes are either glacier-clad or have glaciers in close proximity. Interactions between volcanoes and glaciers are therefore common, and some of the most deadly (e.g., Nevado del Ruiz, 1985) and most costly (e.g., Eyjafjallajökull, 2010) eruptions of recent years were associated with glaciovolcanism. An improved understanding of volcano-glacier interactions is therefore of both global scientific and societal importance. This study investigates the potential of using optical satellite images to detect volcanic impacts on glaciers, with a view to utilise detected changes in glacier surface morphology to improve glacier-clad volcano monitoring and eruption forecasting. Roughly 1400 optical satellite images are investigated from key, well-documented eruptions around the globe during the satellite remote sensing era (i.e., 1972 to present). The most common observable volcanic impact on glacier morphology (for both thick and thin ice-masses) is the formation of ice cauldrons and openings, often associated with concentric crevassing. Other observable volcanic impacts include ice bulging and fracturing due to subglacial dome growth; localized crevassing adjacent to supraglacial lava flows; widespread glacier crevassing, presumably, due to meltwater-triggered glacier acceleration and advance. The main limitation of using optical satellite images to investigate changes in glacier morphology is the availability of cloud- and eruption-plume-free scenes of sufficient spatial- and temporal resolution. Therefore, for optimal monitoring and eruption prediction at glacier-clad volcanoes, optical satellite images are best used in combination with other sources, including SAR satellite data, aerial images, ground-based observations and satellite-derived products (e.g., DEMs).

Volcanic impact on cirrus clouds

<p>Cirrus clouds have a net warming effect on climate due to their high altitude and low optical thickness. Small changes in their properties may however shift this to a stronger warming or a cooling. Aerosol particles can strongly affect cirrus cloud properties since they can act as ice nuclei (IN) for the ice crystals. How downwelling sulfate aerosols from the stratosphere affect cirrus clouds is highly unknown but important both in terms of volcanic impact on climate and possible geoengineering through sulfate injections in the stratosphere. In this study we investigate how the microphysical properties of cirrus clouds change with aerosol loading in the lowermost stratosphere (LMS). The study is focused on the midlatitudes where the descending air motion in the stratosphere result in aerosol downwelling from the stratosphere to the troposphere. The study is conducted during 11 years (2006 - 2016) when the stratosphere had varying levels of aerosol load due to volcanic eruptions. </p><p>The cirrus clouds are studied using the satellite dataset DARDAR (raDAR/liDAR) which combines data from the CloudSat radar and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) lidar. Also the aerosol loading in the LMS is retrieved using a satellite dataset, from CALIPSO (Friberg2018). The first results show that the ice water content of the cirrus clouds decrease when the aerosol loading in the LMS increase. This change occur mainly during spring and autumn for homogeneously frozen cirrus clouds. The results regarding the effective radius of the ice crystals are more uncertain but the effective radius also seem to decrease with increased aerosol loading in the LMS. However, this is mainly seen in the northern hemisphere which has experienced the largest changes in aerosol load due to volcanic eruptions during this period. Also data of ice crystal number concentration are being processed and will be studied to better understand the impact on the cirrus clouds from the downwelling stratospheric aerosol.</p><p><strong>References</strong></p><p>Friberg, J., Martinsson, B. G., Andersson, S. M., and Sandvik, O. S.: Volcanic impact on the climate - The stratospheric aerosol load in the period 2006-2015, Atmospheric Chemistry and Physics, 18, 11 149–11 169, https://doi.org/10.5194/acp-18-11149-2018, 2018.</p>

Sustained volcanic impact and ecosystem disturbance over continental Europe during the Early Holocene

Estimating the environmental and societal impact of recent volcanic eruptions is a task aided by direct measurements and historical sources. Beyond the reach of first-hand accounts, our understanding of pre-historic volcanism is often hindered by the dating uncertainties inherent to stratigraphic archives. Here, we minimise this source of error by analysing the annually laminated sequences of two European lakes. We focus on environmental transformations that occurred in the decades preceding and following the deposition of the Icelandic Saksunarvatn tephra, dated between ca. 10,300 and 10,200 cal. BP. Evidence for continuous eruptive activity pre-dates the tephra deposition by nearly two decades, revealing a period of sustained volcanism and its effects on aquatic and terrestrial ecosystems. These results provide a new insight into the spatial and temporal effects of clustered volcanic eruptions. As such, they might prove useful to refine the simulation of volcanic forcing on continental ecosystems and to evaluate the resilience of prehistoric societies against sudden environmental downturns.

Volcanic impact on the climate – the stratospheric aerosol load in the period 2006–2015

We present a study on the stratospheric aerosol load during 2006–2015, discuss the influence from volcanism and other sources, and reconstruct an aerosol optical depth (AOD) data set in a resolution of 1∘ latitudinally and 8 days timewise. The purpose is to include the “entire” stratosphere, from the tropopause to the almost particle-free altitudes of the midstratosphere. A dynamic tropopause of 1.5 PVU was used, since it enclosed almost all of the volcanic signals in the CALIOP data set. The data were successfully cleaned from polar stratospheric clouds using a temperature threshold of 195 K. Furthermore, a method was developed to correct data when the CALIOP laser beam was strongly attenuated by volcanic aerosol, preventing a negative bias in the AOD data set. Tropospheric influence, likely from upwelling dust, was found in the extratropical transition layer in spring. Eruptions of both extratropical and tropical volcanoes that injected aerosol into the stratosphere impacted the stratospheric aerosol load for up to a year if their clouds reached lower than 20 km altitude. Deeper-reaching tropical injections rose in the tropical pipe and impacted it for several years. Our AODs mostly compare well to other long-term studies of the stratospheric AOD. Over the years 2006–2015, volcanic eruptions increased the stratospheric AOD on average by ∼40 %. In absolute numbers the stratospheric AOD and radiative forcing amounted to 0.008 and −0.2 W m−2, respectively.

Volcanic impact on the climate – the stratospheric aerosol load in the period 2006–2015

We present a study on the stratospheric aerosol load during 2006–2015, discuss the influence from volcanism and other sources, and reconstruct an AOD data-set in a resolution of 1° latitudinally and 8 days timewise. Our attempt is to include the entire stratosphere, from the tropopause to the almost particle free altitudes of the mid-stratosphere. A dynamic tropopause of 1.5 PVU was found to be the best suited one, enclosing almost all of the volcanic signals in the CALIOP data-set. New methods were developed to handle bias in the data. The data were successfully cleaned from polar stratospheric clouds using a temperature threshold of 195 K. Furthermore, a method was developed to correct data when the CALIPSO laser beam was strongly attenuated by volcanic aerosol, preventing a negative bias in the AOD data-set. Tropospheric influence, likely from upwelling dust, was found in the extratropical transition layer in spring. Eruptions of both extratropical and tropical volcanoes that injected aerosol into the stratosphere impacted the stratospheric aerosol load for up to a year if their clouds reached lower than 20 km altitudes, whereas deeper reaching tropical injections rose in the tropical pipe and impacted it for several years. Over the years 2006–2015, volcanic eruptions increased the stratospheric AOD on average by ~ 40 %. In absolute numbers the stratospheric AOD and radiative forcing amounted to 0.008 and −0.2 Wm−2, respectively.

35 yr of stratospheric aerosol measurements at Garmisch-Partenkirchen: from Fuego to Eyjafjallajökull, and beyond

Lidar measurements at Garmisch-Partenkirchen (Germany) have almost continually delivered backscatter coefficients of stratospheric aerosol since 1976. The time series is dominated by signals from the particles injected into or formed in the stratosphere due to major volcanic eruptions, in particular those of El Chichon (Mexico, 1982) and Mt Pinatubo (Philippines, 1991). Here, we focus more on the long-lasting background period since the late 1990s and 2006, in view of processes maintaining a residual lower-stratospheric aerosol layer in absence of major eruptions, as well as the period of moderate volcanic impact afterwards. During the long background period the stratospheric backscatter coefficients reached a level even below that observed in the late 1970s. This suggests that the predicted potential influence of the strongly growing air traffic on the stratospheric aerosol loading is very low. Some correlation may be found with single strong forest-fire events, but the average influence of biomass burning seems to be quite limited. No positive trend in background aerosol can be resolved over a period as long as that observed by lidar at Mauna Loa. We conclude that the increase of our integrated backscatter coefficients starting in 2008 is mostly due to volcanic eruptions with explosivity index 4, penetrating strongly into the stratosphere. Most of them occurred in the mid-latitudes. A key observation for judging the role of eruptions just reaching the tropopause region was that of the plume from the Icelandic volcano Eyjafjallajökull above Garmisch-Partenkirchen (April 2010) due to the proximity of that source. The top altitude of the ash above the volcano was reported just as 9.3 km, but the lidar measurements revealed enhanced stratospheric aerosol up to 14.3 km. Our analysis suggests for two or three of the four measurement days the presence of a stratospheric contribution from Iceland related to quasi-horizontal transport, differing from the strong descent of the layers entering Central Europe at low altitudes. The backscatter coefficients within the first 2 km above the tropopause exceed the stratospheric background by a factor of four to five. In addition, Asian and Saharan dust layers were identified in the free troposphere, Asian dust most likely even in the stratosphere.