ALBERT

Description: There is an urgent need for standardized data collection to better understand permafrost thaw and its interaction with vegetation, hydrology, soil and snow. To enable this, the Permafrost Thaw Action Group of T-MOSAiC have developed a protocol for gathering integrated observations of multiple connected components of permafrost landscapes. It is integrated with a user-friendly app aimed at non-experts to facilitate collection and synthesis of data from across the Arctic. Recognizing the fundamental role of interactions between the different components of the permafrost system, we provide measurement guidelines for variables pertaining to snow, vegetation, hydrology, soil and permafrost in a single protocol. The measured variables include snow depth, vegetation height, water level, soil type, and thaw depth. The protocol locates all measurements on transects that are revisited throughout the year. The co-located measurements of multiple variables facilitate quantification of interactions between these variables and model–data integration. The protocol is geared toward non-experts, including citizen scientists. We provide video tutorials and a user-friendly app. The protocol uses simple measurements that do not require specialist equipment or skills. While variables that are more difficult to measure could not be included, we believe that the simplicity of the protocols will enable greater participation in data collection and thus an improved coverage of the permafrost region. Along with the protocol and app, we present the first results from the data collection which has been live now for several months, and details of how to get involved.

Description: During lithospheric extension, localization of deformation often occurs along structural weaknesses inherited from previous tectonic phases. Such weaknesses may occur in both the crust and mantle, but the combined effects of these weaknesses on rift evolution remain poorly understood. Here we present a series of 3D brittle–viscous analogue models to test the interaction between differently oriented weaknesses located in the brittle upper crust and/or upper mantle. We find that crustal weaknesses usually express first at the surface, with the formation of grabens parallel to their orientation; then, structures parallel to the mantle weakness overprint them and often become dominant. Furthermore, the direction of extension exerts minimal control on rift trends when inherited weaknesses are present, which implies that present-day rift orientations are not always indicative of past extension directions. We also suggest that multiphase extension is not required to explain different structural orientations in natural rift systems. The degree of coupling between the mantle and upper crust affects the relative influence of the crustal and mantle weaknesses: low coupling enhances the influence of crustal weaknesses, whereas high coupling enhances the influence of mantle weaknesses. Such coupling may vary over time due to progressive thinning of the lower crustal layer, as well as due to variations in extension velocity. These findings provide a strong incentive to reassess the tectonic history of various natural examples.

Description: As a rifted margin starts to tilt due to thermal subsidence, evaporitic bodies can become unstable, initiating gravity-driven salt tectonics. Our understanding of such processes has greatly benefitted from tectonic modelling efforts, yet a topic that has however gotten limited attention so far is the influence of large-scale salt basin geometry on subsequent salt tectonics. The aim of this work is therefore to systematically test how salt basin geometry (initial salt basin depocenter location, i.e. where salt is thickest, as well as mean salt thickness) influence salt tectonic systems by means of analogue experiments. These experiments were analyzed qualitatively using top view photography, and quantitatively through Particle Image Velocimetry (PIV), and 3D photogrammetry (Structure-from-Motion, SfM) to obtain their surface displacement and topographic evolution. The model results show that the degree of (instantaneous) margin basin tilt, followed by the mean salt thickness are dominant factors controlling deformation, as enhancing basin tilt and/or mean salt thickness promotes deformation. Focusing on experiments with constant basin tilt and mean salt thickness to filter out these dominant factors, we find that the initial salt depocenter location has various effects on the distribution and expression of tectonic domains. Most importantly, a more upslope depocenter leads to increased downslope displacement of material, and more subsidence (localized accommodation space generation) in the upslope domain when compared to a setting involving a depocenter situated farther downslope. A significant factor in these differences is the basal drag associated with locally thinner salt layers. When comparing our results with natural examples, we find a fair correlation expressed in the links between salt depocenter location and post-salt depositional patterns: the subsidence distribution due to the specific salt depocenter location creates accommodation space for subsequent sedimentation. These correlations are applicable when interpreting the early stages of salt tectonics, when sedimentary loading has not become dominant yet.

Description: This data set includes videos depicting the surface evolution (time laps photographs and Particle Image Velocimetry or PIV analsys) of 15 analogue models on rift tectonics, as well as 4D CT imagery (figures and videos) from four of these experiments. The experiments examined the influence of differently oriented mantle and crustal weaknesses on rift system development using a brittle-viscous set-up. All experiments were performed at the Tectonic Modelling Laboratory of the University of Bern (UB). Detailed descriptions of the experiments and monitoring techniques can be found in Zwaan et al. (2021).

Description: This data set includes videos depicting the surface evolution (time-lapse photographs and Particle Image Velocimetry or PIV analysis) of 38 analogue models, in five model series (A-E), simulating rift tectonics. In these experiments we examined the influence of differently oriented mantle and crustal weaknesses on rift system development during multiphase rifting (i.e. rifting involving changing divergence directions or -rates) using brittle-viscous set-ups. All experiments were performed at the Tectonic Modelling Laboratory of the University of Bern (UB). The brittle and viscous layers, representing the upper an lower crust, were 3 cm and 1 cm thick, respectively, whereas a mantle weakness was simulated using the edge of a moving basal plate (a velocity discontinuity or VD). Crustal weaknesses were simulated using “seeds” (ridges of viscous material at the base of the brittle layers that locally weaken these brittle layers). The divergence rate for the Model A reference models was 20 mm/h so that the model duration of 2:30 h yielded a total divergence of 5 cm (so that e = 17%, given an initial model width of ca. 30 cm). Multiphase rifting model series B and C involved both a slow (10 mm/h) and fast (100 mm/h) rifting phase of 2.5 cm divergence each, for a total of 5 cm of divergence over a 2:45 h period. Multiphase rifting models series D and E had the same divergence rates (20 mm/h) as the Series A reference models, but involved both an orthogonal (α = 0˚) and oblique rifting (α = 30˚) phase of 2.5 cm divergence each, for a total of 5 cm of divergence over a 2:30 h period. In our models the divergence obliquity angle α was defined as the angle between the normal to the central model axis and the direction of divergence. The orientation and arrangements of the simulated mantle and crustal weaknesses is defined by angle θ (defined as the direction of the weakness with respect to the model axis. An overview of model parameters is provided in Table 1, and detailed descriptions of the model set-up and results, as well as the monitoring techniques can be found in Zwaan et al. (2021).