No abstract

Remote mapping and measurement of surface processes at high spatial resolution is among the frontiers in Earth surface process research. Remote measurements that allow meter‐scale mapping of landforms and quantification of landscape change can revolutionize the study of landscape evolution on human timescales. At Mill Gulch in northern California, USA, an active earthflow was surveyed in 2003 and 2007 by airborne laser swath mapping (ALSM), enabling meter‐scale quantification of landscape change. We calculate four‐year volumetric flux from the earthflow and compare it to long‐term catchment average erosion rates from cosmogenic radionuclide inventories from adjacent watersheds. We also present detailed maps of changing features on the earthflow, from which we can derive velocity estimates and infer dominant process. These measurements rely on proper digital elevation model (DEM) generation and a simple surface‐matching technique to align the multitemporal data in a manner that eliminates systematic error in either dataset. The mean surface elevation of the earthflow and an opposite slope that was directly influenced by the earthflow decreased 14 ± 1 mm/yr from 2003 to 2007. By making the conservative assumption that these features were the dominant contributor of sediment flux from the entire Mill Gulch drainage basin during this time interval, we calculate a minimum catchment‐averaged erosion rate of 0·30 ± 0·02 mm/yr. Analysis of beryllium‐10 (10Be) concentrations in fluvial sand from nearby Russian Gulch and the South Fork Gualala River provide catchment averaged erosion rates of 0·21 ± 0·04 and 0·23 ± 0·03 mm/yr respectively. From translated landscape features, we can infer surface velocities ranging from 0·5 m/yr in the wide upper ‘source’ portion of the flow to 5 m/yr in the narrow middle ‘transport’ portion of the flow. This study re‐affirms the importance of mass wasting processes in the sediment budgets of uplifting weak lithologies. Copyright © 2011 John Wiley & Sons, Ltd.

Statistical analysis of geomagnetic paleosecular variation (PSV) and time-averaged field has been largely based on global compilations of paleomagnetic data from lava flows. These show different trends in the averaged inclination anomaly (ΔI) between the two hemispheres, with small positive (<2°) anomalies in midsouthern latitudes and large negative (> −5°) anomalies in midnorthern latitudes. To inspect the large ΔI between 20°N and 40°N we augment the global data with a new paleomagnetic data set from the Golan-Heights (GH), a Plio-Pleistocene volcanic plateau in northeast Israel, located at 32-33°N. The GH data set consists of 91 lava flows sites: 40 sites obtained in the 1990s and 51 obtained in this study. The chronology of the flows is constrained by 57 40 Ar/ 39 Ar ages: 39 from previous studies and 18 from this study, which together cover most of the GH plateau. We show that the 1990s data set might be affected by block rotations and does not fully sample PSV. The Plio-Pleistocene pole (86.3°N, 120.8°E, N = 44, k = 25, α 95 = 4.4°), calculated after applying selection criteria with Fisher precision parameter (k) ≥ 100 and number of specimens per site (n) ≥ 5 is consistent with a geocentric axial dipole field and shows smaller inclination anomaly (ΔI = −0.4°) than predicted by global compilations and PSV models. Reexamination of the inclination anomaly in the global compilation using different calculation methods and selection criteria suggests that inclination anomaly values are affected by (1) inclusion of poor quality data, (2) averaging data by latitude bins, and (3) the way the inclination anomaly is calculated. Plain Language SummarySince the early days of paleomagnetic research it has been inferred that the time-averaged structure of the field is a geocentric axial dipole (GAD)-equivalent to a field generated by a dipole at the center of the Earth aligned with its rotation axis. This so-called GAD hypothesis is fundamental in paleomagnetism and is the basis for plate tectonic reconstructions. However, recent studies have suggested persistent departures from a GAD structure, manifested as an anomaly in the inclination angle of the field in northern hemispheric low to middle latitudes. To address this problem, we analyzed 91 basaltic lava flows from the Golan Heights volcanic plateau in Israel (32-33°N), spanning the past 5 Myr. As each basaltic flow captured the direction of the ambient magnetic field when it cooled, these flows provide us information about the averaged direction of the ancient geomagnetic field. Our results show that the averaged field in the Golan Heights is in agreement with a GAD structure. We also show that if we reanalyze the global paleomagnetic data from lava flows spanning the past 10 Myr using stricter selection criteria and a different inclination anomaly calculation method, the data do not support a global non-GAD field.

Regional and global geomagnetic models of the Holocene, which describe the time evolution of the geomagnetic field vector, are of interest to a number of research fields, including exploration of the geodynamo

The fundamental concept of time-lapse seismic monitoring is that changes in physical parameters—such as saturation, pore fluid pressure, temperature, and stress—affect rock and fluid properties, which in turn alter the seismic velocity and density. Increasingly, however, time-lapse seismic monitoring is called upon to quantify subsurface changes due in part to chemical reactions between injected fluids and the host rocks. This study springs from a series of laboratory experiments and high-resolution images assessing the changes in microstructure, transport, and seismic properties of fluid-saturated sandstones and carbonates injected with [Formula: see text]. Results show that injecting [Formula: see text] into a brine-rock system induces chemo-mechanical mechanisms that permanently change the rock frame. Injecting [Formula: see text] into brine-saturated-sandstones induces salt precipitation primarily at grain contacts and within small pore throats. In rocks with porosity lower than 10%, salt precipitation reduces permeability and increases P- and S-wave velocities of the dry rock frame. On the other hand, injecting [Formula: see text]-rich water into micritic carbonates induces dissolution of the microcrystalline matrix, leading to porosity enhancement and chemo-mechanical compaction under pressure. In this situation, the elastic moduli of the dry rock frame decrease. The results in these two scenarios illustrate that the time-lapse seismic response of chemically stimulated systems cannot be modeled as a pure fluid-substitution problem. A first set of empirical relationships links the time-variant effects of injection to the elastic properties of the rock frame using laboratory velocity measurements and advanced imaging.