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Whilst there has been a recent appreciation for the role of open‐system pingos in providing a fluid‐flow conduit through continuous permafrost that enables methane release, the formation and internal structure of these ubiquitous permafrost‐diagnostic landforms remains unclear. Here, we combine active‐source seismic measurements with electrical resistivity tomography to investigate the structural and subsurface characteristics of an incipient open‐system pingo actively emitting methane within the glacio‐isostatically uplifting fjord valley of Adventdalen, Svalbard. Wavefront inversion of seismic refractions delineate a spatially heterogeneous active layer, whilst deeper reflections identify the lithological boundaries between marine sediments and underlying shales at ∼68 m depth (p‐wave velocity of ∼1,790 ms−1). Low geometric mean inverted resistivities of 40–150 Ωm highlight the dominance of saline permafrost, whilst elevated resistivities (∼2 kΩm) occur close to the groundwater spring and in heaved areas around the pingo. Based on our results, we speculate that segregation ice dominates the pingo structure, given the absence of a notable resistivity contrast characteristic of injection ice that is typically expected within early open‐system pingo formation, and provides the most plausible geomorphic agent within the local fine‐grained sedimentology. Our results thereby indicate that sediment grain size and moisture availability can provide important controls on pingo formation. This study shows that open‐system pingos in coastal, saline permafrost environments may form differently, with implications for localized permafrost structure, its permeability to underlying gas reservoirs and consequent methane release. Plain Language Summary: Considerable amounts of methane, a potent greenhouse gas, can flow through ground which is permanently below freezing (permafrost) through dome‐shaped landforms called open‐system pingos. These landforms occur in the lowlands of mountainous cold regions, from water under pressure from deep underground. However, the formation and internal structure of these landforms are unclear. We use geophysical techniques involving seismic waves and electrical resistivity to characterize the internal structure of a young pingo in Svalbard. Our seismic investigation find a seasonally thawing (active) layer with a variable thickness, and a deeper reflection at ∼68 m which we interpret as the boundary between marine sediments and bedrock. Meanwhile, relatively low electrical resistivities indicate that the ground is saline, and suggest an internal structure that is dominated by discrete layers of ice known as segregated ice, as opposed to a large body of ice which is ordinarily expected. Our results indicate that sediment grain size and moisture availability are important controls on pingo formation. This is important as there may be differences in how these pingos form, and this will impact the structure of local frozen ground and in how they allow the escape of methane stored deep beneath the permafrost. Key Points: Seismic refraction, reflection and electrical resistivity tomography are used to characterize a coastal methane‐emitting incipient pingoLow resistivities and geomorphology preclude massive ice presence, and indicate segregation ice dominates early pingo internal structureSedimentology and moisture availability are critical controls on early pingo formation, and causes plurality within pingo structures [ABSTRACT FROM AUTHOR]

Rapidly-rising jökulhlaups, or glacial outburst floods, are a phenomenon with a high potential for damage. The initiation and propagation processes of a rapidly-rising jökulhlaup are still not fully understood. Seismic monitoring can contribute to an improved process understanding, but comprehensive long-term seismic monitoring campaigns capturing the dynamics of a rapidly-rising jökulhlaup have not been reported so far. To fill this gap, we installed a seismic network at the marginal, ice-dammed lake of the A.P. Olsen Ice Cap (APO) in NE-Greenland. Episodic outbursts from the lake cause flood waves in the Zackenberg river, characterized by a rapid discharge increase within a few hours. Our 6 months long seismic dataset comprises the whole fill-and-drain cycle of the ice-dammed lake in 2012 and includes one of the most destructive floods recorded so far for the Zackenberg river. Seismic event detection and localization reveals abundant surface crevassing and correlates with changes of the river discharge. Seismic interferometry suggests the existence of a thin basal sedimentary layer. We show that the ballistic part of the first surface waves can potentially be used to infer medium changes in both the ice body and the basal layer. Interpretation of time-lapse interferograms is challenged by a varying ambient noise source distribution. [ABSTRACT FROM AUTHOR]

The article discusses the results of a seismic-refraction survey conducted in the upper ablation area of Storglaciären, a valley glacier found in Swedish Lapland. It used the spectral-ratio method on the energy found in the uppermost ice to estimate seismic wave attenuation of the glacier. It proposed the use of a three-phase model of estimating the volumetric content and geometry of air and water within glacier ice to check on electromagnetic speeds to differentiate between dry, bubble free and wet, bubbly glacier ice.

High-magnitude jökulhlaups, glacier margin position and ice-thickness have been identified as key controls on sandur evolution. Existing models however have focused primarily on observations made during short windows of time and often do not account for the subsequent modification of proglacial landsystems by repeated jökulhlaups or post-depositional modification due to melt out over decadal time-scales. Digital Elevation Models (DEMs) were used to reconstruct the development of large depressions on Skeiðarársandur, an outwash plain in southeast Iceland. These depressions measure up to 1 km in width and up to 13 m in depth and are associated with ice bodies up to 1 km in length and up to 150 m in height emplaced during a high-magnitude jökulhlaup in 1903 and subsequently buried by jökulhlaups in 1913 and 1922. The continued melting of the Harðaskriða ice bodies over a century following their emplacement, together with subsequent repeated burial, by high-magnitude jökulhlaups demonstrates that jökulhlaups may continue to serve as important controls on sandur evolution on a decadal to centennial timescale (101–102 years). The Harðaskriða depressions developed only following the retreat of the glacier margin after 1945, which highlights the controls of margin position on the evolution of the sandur. Margin position and thickness of the glacier profile was seen to affect not only the distribution and thickness of sediment emplaced during jökulhaups but also the rate and pattern of melt in the decades following the decoupling of the margin from the sandur. The jökulhlaup landsystem model signatures identified at this site may provide a useful analogue for interpreting landforms and strata emplaced by glacier margin fluctuations, jökulhlaups and melt out generated by retreating continental Pleistocene ice sheets. Unlabelled Image • New model for the origin of large (<1 km wide, <13 m deep) depressions on Skeiðarársandur, southeast Iceland. • 1 km long, 150 m high piece of glacier margin detached and transported during the 1903 high-magnitude jökulhlaup. • Large jökulhlaup-transported ice blocks subsequently buried by jökulhlaups in 1913 and 1922. • Digital Elevation Models (DEMs) and Ground Penetrating Radar (GPR) used to reconstruct the development of depressions. • Jökulhlaup-transported ice bodies continue to melt over a century following their emplacement at an average rate of 19.4 ± 2.6 cm per year. [ABSTRACT FROM AUTHOR]