The open‐system pingos of Svalbard can be divided into three groups. Group I pingos are located over geologic faults. Group II pingos are located in areas of artesian flow resulting from the migration of sub‐glacial groundwater. Pingos of group II occur usually in riverbeds, where the permafrost is locally thinner. Group III pingos are located in nearshore or low‐lying environments of active geologic uplift, where groundwater flow is in response to relict conditions. In this paper group III pingos in the Adventdalen delta area are examined. Group III pingos characteristically have a complex shape and occur in groups. Growth occurs rapidly after initial emergence from marine conditions and the establishment of a minimum permafrost thickness. Water is supplied through discontinuities in the aggrading permafrost. Net influx of water is moderate, owing to relatively thin permafrost.

[1] Six different geophysical investigations, (1) ground-penetrating radar, (2) DC resistivity sounding, (3) seismic refraction, (4) very low frequency (VHF) electromagnetic, (5) helicopter borne electromagnetic (HEM), and (6) transient electromagnetic (TEM) techniques, were employed to obtain information on the ice body properties of pingos near Fairbanks, Alaska. The surface nuclear magnetic resonance (NMR) data were also compared from similar sites near one of the study pingos. The geophysical investigations were undertaken, along with core sampling and permafrost drilling, to enable measurement of the ground temperature regime. Drilling (ground truthing) results support field geophysical investigations, and have led to the development of a technique for distinguishing massive ice and overburden material of the permafrost. The twodimensional DC resistivity sounding tomography and ground-penetrating radar profiling are useful for ice detection under heterogeneous conditions. However, the DC resistivity sounding investigation required high-quality ground contact and less area coverage. The active layer thickness and the homogeneous horizontal structure of the overburden material are important parameters influencing detection of massive ice in permafrost for most methods such as seismic, TEM, or surface NMR.

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Geomorphological and thermohydrological changes to tundra, caused by a wildfire in 2002 on the central Seward Peninsula of Alaska, were investigated as a case study for understanding the response from ice‐rich permafrost terrain to surface disturbance. Frozen and unfrozen soil samples were collected at burned and unburned areas, and then water isotope geochemistry and cryostratigraphy of the active layer and near‐surface permafrost were analyzed to investigate past hydrological and freeze/thaw conditions and how this information could be recorded within the permafrost. The development of thermokarst subsidence due to ice wedge melting after the fire was clear from analyses of historical submeter‐resolution remote sensing imagery, long‐term monitoring of thermohydrological conditions within the active layer, in situ surveys of microrelief, and geochemical signals recorded in the near‐surface permafrost. The resulting polygonal relief coincided with depression lines along an underground ice wedge network, and cumulative subsidence to 2013 was estimated as at least 10.1 to 12.1 cm (0.9–1.1 cm/year 11 year average). Profiles of water geochemistry in the ground indicated mixing or replenishment of older permafrost water with newer meteoric water, as a consequence of the increase in active layer thickness due to wildfire or past thaw event. Our geocryological analysis of cores suggests that permafrost could be used to reconstruct the permafrost degradation history for the study site. Distinct hydrogen and oxygen isotopic compositions above the Global Meteoric Water Line were found for water from these sites where permafrost degradation with geomorphological change and prolonged surface inundation were suggested.

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A transient electromagnetic (TEM) survey was performed for permafrost mapping in Central Alaska, where permafrost is discontinuously distributed. The most stable data were obtained from the measurement of an outside loop with a single‐turn loop of 60×60 m. Electrical sounding was also conducted to evaluate the potential of TEM for permafrost mapping. In permafrost areas, the one‐dimensional inversion results typically show three‐layer geoelectrical sections of resistive subsurface and basement layers separated by a thin conductive layer. The resistive layers of subsurface and basement correspond to permafrost and the top of bedrock, respectively. The second conductive layer indicates an unfrozen state. The ground temperature profiles support these postulated resistivity structures. In permafrost‐free areas, two layers are resolved. The projected thickness of permafrost from the electrical sounding is thinner than the estimates derived from the TEM method. In permafrost‐free areas, results obtained by two methods coincide with each other. We conducted a numerical experiment using synthetic data calculated from a four‐layer permafrost model with appropriate noise for two methods. The inversion procedures show that TEM is better used more precisely for determining the permafrost thickness. Copyright © 2000 John Wiley & Sons, Ltd.

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Deep resistivity structures of permafrost in Siberia were investigated using a transient electromagnetic (TEM) method. The data were compared with temperature profiles. The high and low resistivity layers corresponded to permafrost and a talik, respectively, and the boundary between high and low resistivity was in good agreement with the temperature profile. In TEM surveys conducted from an alas to the taiga forest, the permafrost base was detected at a depth of more than 400 m. This corresponds to the known permafrost depth in this area. A talik was also found to exist at a depth of 100-200 m. Numerical studies indicate that the talik could have been produced by a thermokarst lake. The estimated period after initiation of alas formation agrees with radiocarbon dating results. In combination with the numerical analysis, the geo-electrical information provides a basic model for reconstructing the history of permafrost.