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Permafrost, Icy Soils & Landscapes, and Patterned Ground

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Permafrost, Icy Soils & Landscapes, and Patterned Ground Permafrost, Icy Soils & Landscapes, and Patterned Ground By Bernard Hallet Quaternary Research Center - Dept. of Earth & Space Sciences Patterns in Nature • Patterns in nature can be aesthetically striking • They attract scientific attention (provide a focus) • Excellent research targets: they manifest interesting interactions under conditions that may be particularly instructive (signal is large,little noise) • Invite probing questions and search for deeper Ripples, Eureka Dunes understanding Striking order out of highly random processes Outline • Permafrost: thermal contraction crack polygons • Ice growth in soils • Patterned ground and other landscape features characteristic of permafrost regions Above Beacon Valley, Antarctica Polygonal Patterned Ground, Taylor Valley, Antarctica Sand-wedge polygons, Victoria Valley. Why is the size and micro-topography so variable? Mean T air -23°C From R. Sletten Ice-Wedge Polygons Spacing is a small multiple of crack depth Low-center sand-wedge polygons, ~20m Victoria Valley, Antarctica Sorted circles, Spitsbergen, ~3m Surface patterns contain rich information about the properties and processes active in the less accessible underlying material as on Mars. Stone Stripes, Mauna Kea, ~0.15 m Sorted Stripes, Canadian Rockies • [email protected] Raised Beaches, Spitsbergen Isostatic Uplift due to reduced ice load Stone Circles, Spitsbergen Freezing Clay: Ice lenses (Tabor) Patterns beckon closer attention (from meter to atomic scales) • Sorted circles • Sorting, frost heaving and sorting details • Active layer processes; spatial variation in temperature, thermal properties & moisture • Ice lensing phenomena • Freezing in porous media (soil & rocks) • Premelting behavior; quasi-liquid films Numerical model is consistent with conceptual model base on field observations QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Distinct boundary between fine- grained and stony domains. Wrinkles in algal mat covering the fine- grained soil reflect convergence of soil with the gravel border. Vertical section showing “subduction” of dark, organic rich soil on both sides of gravel ridge When isolated from other patterned ground, “perfect” circles form spontaneously in areas that are wet and level Surface Displacements Scale with Slope Note: vertical 100 scale is not 50 correct; numbers should be 0 divided by 10. -50 Displacement, mm/yr -100 y = - 7.3428 + 144.99x R^2 = 0.466 -150 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 Slope Cross-Section Stone Circle Topography & subsurface Instrumentation: H: heave sensors T: tilt sensors Por: pore pressure transducers Tilt sensors Tilt and Temperature, Spring through Fall Tilt CIXI, Inside Gravel Border Clockwise tilt 3 10 (rotation) is Tilt negative 2 Temperature 1 0 0 -1 Tilt , deg. Temperature, C -2 -3 -4 -10 80 180 280 Julian Days 1988 Residual Tilt (only fall periods shown) Ratchet like, clockwise rotation (~1 deg/yr, full circle in centuries) TILT IN BORDER 1987-1991 2 C1X1- Counterclockwise is positive 0 -2 Tilt, degrees -4 -6 0 1 2 3 4 5 Years Starting September 1987 Distinct Topography Is Sustained, and yet surface material moves downhill everywhere 300 200 1985 100 Elevation, mm 0 1997 -100 0 2 4 6 8 Distance, m Distinct Topography Is Sustained, and yet surface material moves downhill everywhere 300 As material converges on the troughs, and 200 1985 diverges from the ridges, persistence of topography 100 requires subsidence in Elevation, mm troughs, and 0 ascent under 1997 ridges -100 0 2 4 6 8 Distance, m Werner Model Natural Sorted Patterns Pingo (probably closed-system) • [email protected] Mullins Rock Glacier, Antarctica Mima Mound Mystery: lots of ideas about genesis but only 2 cannot be dismissed: seismic shaking and collective activity of colonial gophers..
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