An official website of the United States government
Abstract Temporal changes in seismic velocity estimated from ambient seismic noise can be utilized to infer subsurface properties at volcanic systems. In this study, we process 7 years of continuous seismic noise at Axial Seamount and use cross‐correlation functions to calculate the relative seismic velocity changes (dv/v) beneath the caldera. We find a long‐term trend of decreasing velocity during rapid inflation, followed by slight increase in velocities as background seismicity increases and inflation rate decreases. Furthermore, we observe small short‐term increases indv/vwhich coincide with short‐term deflation events. Our observations of changes indv/vand their correlation with other geophysical data provide insights into how the top ∼1 km of the crust at Axial Seamount changes in response to subsurface magma movement and capture the transition from a period of rapid reinflation to a period where the caldera wall faults become critically stressed and must rupture to accommodate further inflation.
more »
« less
Monitoring Seasonal Fluctuation and Long‐Term Trends for the Greenland Ice Sheet Using Seismic Noise Auto‐Correlations
Abstract One important feature of the Greenland Ice Sheet (GrIS) change is its strong seasonal fluctuation. Taking advantage of deployed seismographic stations in Greenland, we apply cross‐component auto‐correlation of seismic ambient noise to measure in‐situ near surface relative velocity change (dv/v) in different regions of Greenland. Our results demonstrate thatdv/vmeasurements for most stations have less than 3 months lag times in comparison to the surface mass change. These various lag times may provide us constraints for the thickness of the subglacial till layer over different regions in Greenland. Moreover, in southwest Greenland, we observe a change in the long‐term trend ofdv/vfor three stations, which might be consistent with the mass change rate (dM/dt) due to the “2012–2013 warm‐cold transition.” These observations suggest that seismic noise auto‐correlation technique may be used to monitor both seasonal and long‐term changes of the GrIS.
more »
« less
- Award ID(s):
- 2042098
- PAR ID:
- 10405222
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 50
- Issue:
- 7
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Significant imbalances in terrestrial water storage (TWS) and severe drought have been observed around the world as a consequence of climate changes. Improving our ability to monitor TWS and drought is critical for water‐resource management and water‐deficit estimation. We use continuous seismic ambient noise to monitor temporal evolution of near‐surface seismic velocity,dv/v, in central Oklahoma from 2013 to 2022. The deriveddv/vis found to be negatively correlated with gravitational measurements and groundwater depths, showing the impact of groundwater storage on seismic velocities. The hydrological effects involving droughts and recharge of groundwater occur on a multi‐year time scale and dominate the overall derived velocity changes. The thermoelastic response to atmospheric temperature variations occurs primarily on a yearly timescale and dominates the superposed seasonal velocity changes in this study. The occurrences of droughts appear simultaneously with local peaks ofdv/v, demonstrating the sensitivity of near‐surface seismic velocities to droughts.more » « less
-
Abstract Mass loss of the Greenland Ice Sheet (GrIS) plays a major role in the global sea level rise. The west coast of the GrIS has contributed 1,000 Gt of the 4,488 Gt GrIS mass loss between 2002 and 2021, making it a hotspot for GrIS mass loss. Surface melting is driven by changes in the radiative budget at the surface, which are modulated by clouds. Previous works have shown the impact of North Atlantic transport for influencing cloudiness over the GrIS. Here we used space‐based lidar cloud profile observations to show that a polar low circulation promotes the presence of low clouds over the GrIS west coast that warm radiatively the GrIS surface during the melt season. Polar low circulation transports moisture and low clouds from the sea to the west of Greenland up over the GrIS west coast through the melt season. The concomitance of the increasing presence of low cloud in fall over the Baffin Sea due to seasonal sea‐ice retreat and a maximum occurrence of Polar low circulation in September results in a maximum of low cloud fraction (∼14% at 2.5 km above sea level) over the GrIS west coast in September. These low clouds warm radiatively the GrIS west coast surface up to 80 W/m2locally. This warming contributes to an average increase of 10 W/m2of cloud surface warming in September compared to July on the GrIS west coast. Overall, this study suggests that regional atmospheric processes independent from North Atlantic transport may also influence the GrIS melt.more » « less
-
Abstract. The Greenland Ice Sheet (GrIS) rapid mass loss is primarily driven by an increase in meltwater runoff, which highlights the importance of understanding the formation, evolution, and impact of meltwater features on the ice sheet. Buried lakes are meltwater features that contain liquid water and exist under layers of snow, firn, and/or ice. These lakes are invisible in optical imagery, challenging the analysis of their evolution and implication for larger GrIS dynamics and mass change. Here, we present a method that uses a convolutional neural network, a deep learning method, to automatically detect buried lakes across the GrIS. For the years 2018 and 2019 (which represent low- and high-melt years, respectively), we compare total areal extent of both buried and surface lakes across six regions, and we use a regional climate model to explain the spatial and temporal differences. We find that the total buried lake extent after the 2019 melt season is 56 % larger than after the 2018 melt season across the entire ice sheet. Northern Greenland has the largest increase in buried lake extent after the 2019 melt season, which we attribute to late-summer surface melt and high autumn temperatures. We also provide evidence that different processes are responsible for buried lake formation in different regions of the ice sheet. For example, in southwest Greenland, buried lakes often appear on the surface during the previous melt season, indicating that these meltwater features form when surface lakes partially freeze and become insulated as snowfall buries them. Conversely, in southeast Greenland, most buried lakes never appear on the surface, indicating that these features may form due to downward percolation of meltwater and/or subsurface penetration of shortwave radiation. We provide support for these processes via the use of a physics-based snow model. This study provides additional perspective on the potential role of meltwater on GrIS dynamics and mass loss.more » « less
-
Abstract. Numerical simulations of the Greenland Ice Sheet (GrIS) over geologictimescales can greatly improve our knowledge of the critical factors drivingGrIS demise during climatically warm periods, which has clear relevance forbetter predicting GrIS behavior over the upcoming centuries. To assess thefidelity of these modeling efforts, however, observational constraints ofpast ice sheet change are needed. Across southwestern Greenland, geologicrecords detail Holocene ice retreat across both terrestrial-based and marine-terminating environments, providing an ideal opportunity to rigorouslybenchmark model simulations against geologic reconstructions of ice sheetchange. Here, we present regional ice sheet modeling results using theIce-sheet and Sea-level System Model (ISSM) of Holocene ice sheet historyacross an extensive fjord region in southwestern Greenland covering thelandscape around the Kangiata Nunaata Sermia (KNS) glacier and extendingoutward along the 200 km Nuup Kangerula (Godthåbsfjord). Oursimulations, forced by reconstructions of Holocene climate and recentlyimplemented calving laws, assess the sensitivity of ice retreat across theKNS region to atmospheric and oceanic forcing. Our simulations reveal thatthe geologically reconstructed ice retreat across the terrestrial landscapein the study area was likely driven by fluctuations in surface mass balancein response to Early Holocene warming – and was likely not influencedsignificantly by the response of adjacent outlet glaciers to calving andocean-induced melting. The impact of ice calving within fjords, however,plays a significant role by enhancing ice discharge at the terminus, leadingto interior thinning up to the ice divide that is consistent withreconstructed magnitudes of Early Holocene ice thinning. Our results,benchmarked against geologic constraints of past ice-margin change, suggestthat while calving did not strongly influence Holocene ice-margin migrationacross terrestrial portions of the KNS forefield, it strongly impactedregional mass loss. While these results imply that the implementation andresolution of ice calving in paleo-ice-flow models is important towardsmaking more robust estimations of past ice mass change, they also illustratethe importance these processes have on contemporary and future long-term icemass change across similar fjord-dominated regions of the GrIS.more » « less
