Volcanoes stunt nearby glaciers

Abstract

Glacierised volcanoes pose significant hazards to societies. Monitoring these volcanoes is therefore essential, though challenging, as traditional geophysical and geochemical methods for tracking volcanic activity can be hindered by glacier cover or remoteness. In this study, we analyse to what extent 307 active volcanoes worldwide impact the mass balance of glaciers within a 40 km radius, a total of 40667 glaciers, by comparing their relative median elevations. We show that glaciers near volcanoes are progressively confined to higher elevations closer to volcanoes, indicating that volcanic processes have a negative impact on nearby glacier mass balance. The influence of noneruptive and eruptive volcanic activity on glacier mass balance is primarily confined to glaciers within 5 km of volcanoes, a similar footprint to detected anomalies in thermal and deformation studies. Our results present a global assessment of volcanic effects on glacier mass balance, and could serve as a baseline for future monitoring efforts of how volcanic activity affects glaciers.

Fig. 1. Schematic and example of higher median glacier elevations near volcanoes.

a An illustration demonstrating how median glacier elevations (solid lines and x's in inset graph) rise towards volcanoes. The colour gradient of the median elevations indicates the relative median glacier elevations, computed as the deviation from the mean (dashed yellow line): relative median glacier elevations closer to volcanoes are positive (red), but trend to negative (blue) further away. b An example of median glacier elevations rising towards Mount Wrangell volcano (black star), Alaska. The glaciers within 40 km of Mount Wrangell are coloured according to their relative median elevation. The dashed boxes are to highlight the debris-covered glaciers and dry-calving glaciers of Sanford (1) and Drum (2). The base map is a shaded relief of the ASTER GDEM V003.

Fig. 2. Global prevalence of higher median glacier elevations around volcanoes.

The local trend of median glacier elevations (MGE) for 5 km around glacierised volcanoes. Red and blue dots denote rising and lowering, respectively, median glacier elevations towards volcanoes based on the Spearman’s Rho test. Up to 80% of Earth’s volcanoes demonstrate higher median glacier elevations closer to volcanoes (Table 1). The basemap was made with Natural Earth (naturalearthdata.com).

Fig. 3. Trend analysis of median glacier elevations surrounding volcanoes.

The correlation coefficients of different tests of the local trends of median glacier elevations for 5 km around each glacierised volcano, shown as individual values (black dots), median and quartile values (dark blue box plots), and value distribution (light blue ridge plots). The trend tests are: linear regression (LR), Mann-Kendall trend test (MK), and Spearman’s Rho test (SR). A correlation coefficient of 0 means no trend,  ±1 indicates a perfect linear and/or monotonic trend, and the sign denotes the direction of the trend away from volcanoes. The trend tests show a definite negative correlation between median glacier elevations and the distance from volcanoes, i.e., median glacier elevations generally fall moving away from volcanoes.

Fig. 4. The trend of all median elevations of all glaciers around all volcanoes.

Relative median glacier elevations for all glaciers (gray dots) within 20 km of all volcanoes, a total of 14366 glaciers. The median glacier elevations are shown as relative to the average within the radial search areas. To highlight the general trend, a smoothed moving average (black lines) is shown of the relative minimum- (dotted line), median- (solid line), and maximum (dashed line) glacier elevations. A clear rise in median glacier elevations can be seen towards volcanoes within a distance of 5 km (red solid line), but beyond 5 km there is no trend (red dashed line).

Fig. 5. Global distribution of glaciers and volcanoes, highlighting glacierised volcanoes.

Holocene volcanoes (red dots) from the Global Volcanism Program, and glaciers (blue polygons) and first-order regions (black polygons) from the Randolph Glacier Inventory. The glacierised volcanoes analysed in this study (triangles) are volcanoes with glaciers within a distance of 5 km (red), 10 km (dark orange), 20 km (light orange), and 40 km (yellow). The basemap was made with Natural Earth (naturalearthdata.com). Antarctic volcanoes, i.e., volcanoes within RGI region 20, are here excluded from the list of glacierised volcanoes. Enlarged insets of the areas with the highest concentration of glacierised volcanoes (dashed boxes a–d) are shown in Fig. S5.