Fluid Dynamics of the Solid Earth

Transcription

1 Fluid Dynamics of the Solid Earth Jerome A. Neufeld, M. Grae Worster MWF, , MR13

2 Patterns of global seismicity Earthquake Magnitude Earthquake Depth (km) Plate Boundaries Active Volcanoes Global Earthquakes

3 Structure of Earth s interior from seismic tomography

4 Structure of Earth s interior Oceanic crust (6 km) Athenosphere 410 km 660 km 2900 km Sea water (0 8 km) Continental crust (20 90 km) D Lower mantle Lithosphere ( km) Upper mantle Transition zone depth (km) V p,v s (km/s) upper mantle transition zone lower mantle outter core crust D laterally heterogenious Mohorovicic discontinuity phase change to high pressure polymorphs velocity increase primarily from pressure increase laterally heterogenious (Temp. & composition) core mantle boundary convecting liquid Iron nickle sulphur mixture lithosphere "rigid" asthenosphere "plastic" 5100 km 6371 km Outer core Inner core 6000 inner core solid anisotropic (kg/m 3) ρ

5 Solidification of Earth s inner core and the magnetic field Magnetism geomagnetic field

6 sea ice formation ammonium chloride mushy layer

7 Solidification driven by cooling, convection by salt (some heat) ammonium chloride sea ice

8 Growth and waning of Arctic sea ice

9 Large scale flow of glacial ice Axel Heiberg Island, Canadian Arctic

10 LETTERS On the eve of the international polar year, international space agencies worked together to enable a complete InSAR survey of Antarctica. We used spring 2009 data from RADARSAT-2 [Canadian Space Agency (CSA) and MacDonald, Dettwiler, and Associates Limited (MDA)]; spring 2007, 2008, and 2009 data from Envisat ASAR [European Space Agency n (ESA)]; and fall 2007 to 2008 data from the Advanced Land Observing Satellite (ALOS) PALSAR [Japan Aerospace Exploration Agency (JAXA)], complemented by patches of CSA s RADARSAT-1 data from fall 2000 (7) and ESA s Earth Remote-Sensing Satellites 1 and 2 (ERS-1/2) data from spring 1996 (2). Each radar instrument contributes its unique coverage and performance level (fig. S1). The final mosaic assembles 900 satellite tracks and more than 3000 orbits of radar data (Fig. 1). The data are georeferenced with a precision better than one pixel, here 300 m, to an Earth-fixed grid by using a digital elevation model (DEM) 0.02 (8). Absolute calibration of the surface velocity data relies on control points of zero motion dis0.0tributed yr 1 along the coast (stagnant areas near ice domes or emergent mountains) and along major ice divides (areas of zero surface slope in the DEM) in a set of coast-to-coast advanced syn 0.02 thetic aperture radar (ASAR) tracks (fig. S1) s 1 yr 1precision varies with instrument, Themmapping location, technique of analysis, repeat cycle, time period, and data stacking. Nominal errors range from 1 m/year along major ice divides with high data stacking to about 17 m/year in areas affected by ionospheric perturbations (fig. S2). In terms of strain rate, or changes in velocity per unit length, data noise is at the per year level, which is sufficient to reveal effective strain rates along tributary shear margins over the vast majority of the continent (Fig. 2A). Ice velocity ranges from a few cm/year near divides to a few km/year on fast-moving glaciers and floating ice shelves, or 5 orders of magnitude. The histogram in surface velocity has a bimodal distribution with a main peak at 4 to 5 m/year, corresponding to slow motion in East Antarctica, and a second peak at 250 m/year, driven by the fast flow of glaciers and ice shelves. The fastest glaciers, Pine Island and Thwaites, are several times faster than any other glacier Antarctic sea ice (conc, vel) a b 1428 wide ice motion accurately. Figure 1 reveals a wealth of new information. For instance, the exact pathway of ice along the coastline is not without surprise. In Queen Maud Land, the main trunk of Jutulstraumen is not to the south through Penck trough but to the east of Neumayer Cliffs (10). The Sør Rondane Mountains were known to deflect ice flow to the east and to the west massive rates of basal ablation of the ice shelves by the underlying warm ocean (13). An interesting aspect is the spatial pattern of tributary flow. Each major glacier is the merger of several tributaries that extend hundreds of km inland. Although this was observed in the pardoi: /NGEO tial mapping of Siple Coast (14) and Pine Island (15), this is now observed over the entire ice sheet. NATURE GEOSCIENCE Antarctic glacial ice (vel) waters in the ice-melting zone. In areas of mean northerly w (Bellingshausen, Cosmonaut and Dumont D Urville seas; Fig southward advection opposes thermodynamic growth of th cover, and freezing extends closer to the ice edge. The mean concentration difference over autumn is domin by freezing, with advection and divergence being minor con utors during this period (Supplementary Fig. S2). Howeve the Pacific sector and Weddell Sea, trends in the autumn centration difference seem to be strongly influenced by dyna (Supplementary Fig. S3). In contrast, trends in the King H Sea are controlled by thermodynamics. Supplementary Fig shows the proportion of the autumn concentration differ trend that is explained by trends in dynamical processes. The is noisy, but after heavy smoothing, it confirms that dyn trends dominate in the Pacific sector. Trends in freezing in sector can actually oppose the ice-concentration changes, bec dynamical processes are progressively replacing thermodyna Ice-concentration losses in the Weddell Sea also seem to be ca by decreased northward advection, but the concentration inc in King Håkon Sea and other changes around East Antar contain a strong thermodynamic component. The wind tren these regions suggest that changes in cold- and warm-air adve explain thevelocity thermodynamic trends. Fig. 1. Antarctic ice derived from ALOS PALSAR, Envisat ASAR, RADARSAT-2, and ERS-1/2 satellite radar interferometry, color-coded on a logarithmic scale, and overlaid on a MODISlies mosaic The ultimate cause of the wind and ice changes inofthe l Antarctica (22), with geographic names discussed in the text. Pixel spacing is 300 m. Projection is polar scale atclimate oflines thedelineate Southern stereographic 71 S secantvariability plane. Thick black major icehemisphere. divides (2). Thin blackantarcti lines outlineice subglacial lakes discussed in the text. Thick black lines along the coast are interferometrically can contain 3 5-year cyclic anomalies that might be p derived ice sheet grounding lines (23). aliased into our calculations1,16,21, but our trends cover se suchvolcycles and are consistent with longer-term studies18. As 9 SEPTEMBER SCIENCE of the wind trends (and therefore ice-motion trends) ca

11 Magma chambers: Dynamics of emplacement and solidification Cuernos del Paine laccolith, Torres del Paine National Park, Chile laccolith elastic overburden feeder dike

12 Continental deformation of Tibetan Plateau Zhang et al. Geology (2004)

13 Representative course calendar L1 Fri, Jan 19 General introduction: plate cooling model of the oceanic lithosphere (JAN) L2 Mon., Jan 22 Onset of convection - mantle convection and the plate cooling model (JAN) L3 Wed., Jan 24 High Ra convection (JAN) L4 Fri, Jan 26 The Stefan condition: similarity solutions, quasi-steady approximation (MGW) L5 Mon, Jan 29 The Stefan condition: external heat flux (MGW) L6 Wed., Jan 31 The Stefan condition: application to the growth of the Earth s inner core (MGW) L7 Fri., Feb 2 Sea ice: radiation, albedo (MGW) L8 Mon., Feb 5 Sea ice: 2 category model, mixed layer ocean (MGW) L9 Wed., Feb 7 Darcy s law: gravity currents in porous media (unconfined) (JAN) L10 Fri., Feb 9 Darcy s law: gravity currents in porous media (confined and with leakage) (JAN) L11 Mon., Feb 12 Darcy s law: leakage from gravity currents (JAN) L12 Wed., Feb 14 Darcy s law: residual trapping and self-similar solutions of the 2nd type (JAN) L13 Fri., Feb 16 Convection in porous media: closed aquifer model, flux o a gravity current (JAN) L14 Mon., Feb 19 Introduction to alloys: phase diagrams (MGW) L15 Wed., Feb 21 melting/dissolution (MGW) L16 Fri., Feb 23 Thermodynamic models of sea ice (MGW) L17 Mon., Feb 26 Multiphase flows: viscous compaction & mantle upwelling (JAN) L18 Wed., Feb 28 Multiphase flows: poroelasticity and pressure di usion (JAN) L19 Fri., Mar 2 Terrestrial ice sheets (MGW) L20 Mon., Mar 5 Ice-shelf dynamics, extensional flows, tabular icebergs (MGW) L21 Wed., Mar 7 Grounding-line dynamics, dynamic flotation condition, confined ice sheets (MGW) L22 Fri., Mar 9 Magma propagation: formation of dykes and laccoliths (JAN) L23 Mon., Mar 12 Fracturing and faulting (JAN) L24 Wed., Mar 14 Mountain building: viscous deformation, post-glacial rebound (MGW) Examples classes: 1400 Feb 5, 1600 Feb 19, 1400 Mar 12, 1400 Apr 30

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15 Magnetic anomalies and spreading sea floor

16 Sea floor depth with age (distance) Pacific plate Depth (m) Stein & Stein (1992) Pacific, this study, a = 90 km Parsons & Sclater (1977) Age (Ma) Crosby, McKenzie, Sclater. Geophys. J. Int. (2006)