Earth's present-day response to enhanced glacial melting resulting from climate change can be measured using Global Positioning System (GPS) technology. We present data from 62 continuously operating GPS instruments in Iceland. Statistically significant upward velocity and accelerations are recorded at 27 GPS stations, predominantly located in the Central Highlands region of Iceland, where present-day thinning of the Iceland ice caps results in velocities of more than 30 mm/yr and uplift accelerations of 1-2 mm/yr 2 . We use our acceleration estimates to back calculate to a time of zero velocity, which coincides with the initiation of ice loss in Iceland from ice mass balance calculations and Arctic warming trends. We show, through a simple inversion, a direct relationship between ice mass balance measurements and vertical position and show that accelerated unloading is required to reproduce uplift observations for a simple elastic layer over viscoelastic half-space model.

[1] Vegetation bands are periodic bands of vegetation, separated by interband spaces devoid of vegetation, oriented parallel to the topographic contour in some gently sloping arid to semiarid environments. Models of vegetation band formation attribute their formation to positive feedbacks among vegetation density, soil porosity/permeability, and infiltration rates. Here we present an alternative model based on field measurements at our study sites in southern Nevada. In this model, interband spaces between vegetation bands form because topographic mounds beneath vegetation bands detain water upslope from vegetation bands, leading to hydrologic and sedimentologic conditions that inhibit the survival of plants in interband spaces. We used terrestrial laser scanning (TLS) to create high-resolution ($10 cm 2 /pixel) raster data sets of bare-earth topography and canopy height for four study sites. Analyses of the TLS data, in addition to measurements of soil shear strength and particle size, document the potential for detention in interband spaces and a near-inverse proportionality between band spacing and regional slope. We describe a cellular automaton model (herein called model 1) for vegetation band formation that includes just two user-defined parameters and that generates vegetation bands similar to those at our field sites, including the inverse proportionality between spacing and regional slope. A second model (model 2) accurately predicts the width of vegetation bands in terms of the number and spacing of plants and the geometry of individual plant mounds. We also present a GIS-based analysis that predicts where bands occur within a region based on topographic and hydroclimatic controls.

As the global climate changes, understanding short‐term variations in water storage is increasingly important. Continuously operating Global Positioning System (cGPS) stations in Iceland record annual periodic motion—the elastic response to winter accumulation and spring melt seasons—with peak‐to‐peak vertical amplitudes over 20 mm for those sites in the Central Highlands. Here for the first time for Iceland, we demonstrate the utility of these cGPS‐measured displacements for estimating seasonal and shorter‐term ice cap mass changes. We calculate unit responses to each of the five largest ice caps in central Iceland at each of the 62 cGPS locations using an elastic half‐space model and estimate ice mass variations from the cGPS time series using a simple least squares inversion scheme. We utilize all three components of motion, taking advantage of the seasonal motion recorded in the horizontal. We remove secular velocities and accelerations and explore the impact that seasonal motions due to atmospheric, hydrologic, and nontidal ocean loading have on our inversion results. Our results match available summer and winter mass balance measurements well, and we reproduce the seasonal stake‐based observations of loading and melting within the 1 σ confidence bounds of the inversion. We identify nonperiodic ice mass changes associated with interannual variability in precipitation and other processes such as increased melting due to reduced ice surface albedo or decreased melting due to ice cap insulation in response to tephra deposition following volcanic eruptions, processes that are not resolved with once or twice‐yearly stake measurements.

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