Patterns in glacial-earthquake activity around Greenland, 2011–13

KIRA G. OLSEN; MEREDITH NETTLES

doi:10.1017/jog.2017.78

Patterns in glacial-earthquake activity around Greenland, 2011–13

Journal of Glaciology ◽

10.1017/jog.2017.78 ◽

2017 ◽

Vol 63 (242) ◽

pp. 1077-1089 ◽

Cited By ~ 6

Author(s):

KIRA G. OLSEN ◽

MEREDITH NETTLES

Keyword(s):

Remote Sensing ◽

Mass Loss ◽

West Coast ◽

Source Parameters ◽

Greenland Ice Sheet ◽

Earthquake Activity ◽

Earthquake Catalog ◽

The Past ◽

Earthquake Force ◽

Iceberg Calving

ABSTRACTGlacial earthquakes are caused by large iceberg calving events, which are an important mechanism for mass loss from the Greenland ice sheet. The number of glacial earthquakes in Greenland has increased sixfold over the past two decades. We use teleseismic surface waves to analyze the 145 glacial earthquakes that occurred in Greenland from 2011 through 2013, and successfully determine source parameters for 139 events at 13 marine-terminating glaciers. Our analysis increases the number of events in the glacial-earthquake catalog by nearly 50% and extends it to 21 years. The period 2011–13 was the most prolific 3-year period of glacial earthquakes on record, with most of the increase over earlier years occurring at glaciers on Greenland's west coast. We investigate changes in earthquake productivity and geometry at several individual glaciers and link patterns in glacial-earthquake production and cessation to the absence or presence of a floating ice tongue. We attribute changes in earthquake force orientations to changes in calving-front geometry, some of which occur on timescales of days to months. Our results illustrate the utility of glacial earthquakes as a remote-sensing tool to identify the type of calving event, the grounded state of a glacier, and the orientation of an active calving front.

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Mass balance of the Greenland ice sheet – a study of ICESat data, surface density and firn compaction modelling

The Cryosphere Discussions ◽

10.5194/tcd-4-2103-2010 ◽

2010 ◽

Vol 4 (4) ◽

pp. 2103-2141 ◽

Cited By ~ 3

Author(s):

L. S. Sørensen ◽

S. B. Simonsen ◽

K. Nielsen ◽

P. Lucas-Picher ◽

G. Spada ◽

...

Keyword(s):

Remote Sensing ◽

Mass Loss ◽

Mass Balance ◽

Volume Change ◽

Surface Density ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Altimetry Data ◽

Data Set ◽

Elevation Changes

Abstract. ICESat has provided surface elevation measurements of the ice sheets since the launch in January 2003, resulting in a unique data set for monitoring the changes of the cryosphere. Here we present a novel method for determining the mass balance of the Greenland ice sheet derived from ICESat altimetry data. Four different methods for deriving the elevation changes from the ICESat altimetry data set are used. This multi method approach gives an understanding of the complexity associated with deriving elevation changes from the ICESat altimetry data set. The altimetry can not stand alone in estimating the mass balance of the Greenland ice sheet. We find firn dynamics and surface densities to be important factors in deriving the mass loss from remote sensing altimetry. The volume change derived from ICESat data is corrected for firn compaction, vertical bedrock movement and an intercampaign elevation bias in the ICESat data. Subsequently, the corrected volume change is converted into mass change by surface density modelling. The firn compaction and density models are driven by a dynamically downscaled simulation of the HIRHAM5 regional climate model using ERA-Interim reanalysis lateral boundary conditions. We find an annual mass loss of the Greenland ice sheet of 210 ± 21 Gt yr−1 in the period from October 2003 to March 2008. This result is in good agreement with other studies of the Greenland ice sheet mass balance, based on different remote sensing techniques.

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Glacier dynamics over the last quarter of a century at Jakobshavn Isbræ

The Cryosphere Discussions ◽

10.5194/tcd-9-4865-2015 ◽

2015 ◽

Vol 9 (5) ◽

pp. 4865-4892

Author(s):

I. S. Muresan ◽

S. A. Khan ◽

A. Aschwanden ◽

C. Khroulev ◽

T. Van Dam ◽

...

Keyword(s):

Mass Loss ◽

Sea Level Rise ◽

Sea Level ◽

21St Century ◽

Greenland Ice Sheet ◽

Outlet Glacier ◽

The Past ◽

Glacier Dynamics ◽

The Future ◽

Oceanic Forcing

Abstract. Observations over the past two decades show substantial ice loss associated with the speedup of marine terminating glaciers in Greenland. Here we use a regional 3-D outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in west Greenland. Using atmospheric and oceanic forcing we tune our model to reproduce the observed frontal changes of JI during 1990–2014. We identify two major accelerations. The first occurs in 1998, and is triggered by moderate thinning prior to 1998. The second acceleration, which starts in 2003 and peaks in summer 2004, is triggered by the final breakup of the floating tongue, which generates a reduction in buttressing at the JI terminus. This results in further thinning, and as the slope steepens inland, sustained high velocities have been observed at JI over the last decade. As opposed to other regions on the Greenland Ice Sheet (GrIS), where dynamically induced mass loss has slowed down over recent years, both modelled and observed results for JI suggest a continuation of the acceleration in mass loss. Further, we find that our model is not able to capture the 2012 peak in the observed velocities. Our analysis suggests that the 2012 acceleration of JI is likely the result of an exceptionally long melt season dominated by extreme melt events. Considering that such extreme surface melt events are expected to intensify in the future, our findings suggest that the 21st century projections of the GrIS mass loss and the future sea level rise may be larger than predicted by existing modelling results.

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Hydrological and Kinematic Precursors of Iceberg Calving at Petermann Glacier in Northern Greenland Observed High-temporal Resolution Sentinel-2 Images

10.5194/egusphere-egu2020-7831 ◽

2020 ◽

Author(s):

Daan Li ◽

Liming Jiang

Keyword(s):

Remote Sensing ◽

High Resolution ◽

Sea Ice ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Flow Speed ◽

High Temporal Resolution ◽

Backscatter Coefficient ◽

Ice Flow ◽

Iceberg Calving

<p>&#160; &#160;The Greenland ice sheet is currently contributing to global sea level at an approximate rate of 0.8 mm/yr. Ice mass loss of Greenland is primarily due to both thinning and retreat of outlet glaciers. For enhanced calving events, detail dynamics characteristics of hydrological and kinematic precursors and underlying mechanisms which control the development of ice calving remain poorly understood, especially in the absence of high-resolution remote sensing observations. On July 26 2017, a calving event took place along a pre-existing rift in Petermann glacier, northern Greenland, which removed partly of the glacier tongue and formed a tabular iceberg 5 km long. In this study, we used high-temporal satellite remote sensing data to detect changes in ice-flow speed, melt ponds and ice m&#233;lange during May and July. These hydrological and kinematic dynamics derived from Sentinel-1/2 satellite images with sub-weekly acquisition repeat cycles can be utilized as retreat precursors to characterize the detailed calving process. Moreover, the stress field and analytical damage solution were calculated by coupling the remote sensing observations with SSA ice sheet model to explain the dynamics mechanism. Our preliminary results show that the ice speed in dense observation reached to 30 m/d on the eve of the calving, which is roughly 10 times quicker than usual ice velocity. Additionally, there exited obviously abnormal stress distribution in crack region. And the landfast sea ice and ice m&#233;lange transformed into open water that the &#160;backscatter coefficient decreased to 28 dB. The extent of melt pond reached the peak about 30 square kilometers coverage in duration month of calving event. It is inferred that this calving event of Petermann glacier may be related to weakening of sea ice and ice m&#233;lange lost the buttressing for ice glacier terminate, tributary glacier extrusion, related with meltwater in&#64257;ltrated crevasses. Therefore, dense remote sensing observations and numerical modeling in ice flow system make it possible for early waring and projecting glacier calving in the future.</p><p>Key words: Iceberg Calving Precursors, Petermann Glacier, High Resolution Remote Sensing, SSA modeling</p>

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Recent Precipitation Decrease Across the Western Greenland Ice Sheet Percolation Zone

10.5194/tc-2019-103 ◽

2019 ◽

Author(s):

Gabriel Lewis ◽

Erich Osterberg ◽

Robert Hawley ◽

Hans Peter Marshall ◽

Tate Meehan ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Climate Models ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Regional Climate Models ◽

The Past ◽

Precipitation Decrease ◽

Percolation Zone

Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest to scientists and the general public in the context of future sea-level rise. Increased melting in the GrIS percolation zone due to atmospheric warming over the past several decades has led to increased mass loss at lower elevations. Previous studies have hypothesized that this warming is accompanied by a precipitation increase, as would be expected from the Clausius-Clapeyron relationship, negating some of the melt-induced mass loss throughout the Western GrIS. This study tests that hypothesis by calculating snow accumulation rates and trends across the Western GrIS percolation zone, providing new critical accumulation estimates in regions with sparse and/or dated in situ data for calibration of future regional climate models. We present accumulation records from sixteen 22–32 m long firn cores and 4436 km of ground penetrating-radar, covering the past 20–60 years of accumulation, collected across the Western GrIS percolation zone as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Trends from both radar and firn cores, as well as commonly used regional climate models, show decreasing accumulation and precipitation over the 1996–2016 period, which we attribute to shifting storm-tracks related to stronger atmospheric summer blocking over Greenland. Changes in atmospheric circulation over the past 20 years, specifically anomalously high summertime blocking, have reduced GrIS surface mass balance through both an increase in surface melting and a decrease in accumulation.

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Recent precipitation decrease across the western Greenland ice sheet percolation zone

The Cryosphere ◽

10.5194/tc-13-2797-2019 ◽

2019 ◽

Vol 13 (11) ◽

pp. 2797-2815 ◽

Cited By ~ 4

Author(s):

Gabriel Lewis ◽

Erich Osterberg ◽

Robert Hawley ◽

Hans Peter Marshall ◽

Tate Meehan ◽

...

Keyword(s):

Mass Loss ◽

Mass Balance ◽

Accumulation Rate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Snow Accumulation ◽

Accumulation Rates ◽

The Past ◽

Precipitation Decrease ◽

Percolation Zone

Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest in the context of future sea level rise. Increased melting in the GrIS percolation zone due to atmospheric warming over the past several decades has led to increased mass loss at lower elevations. Previous studies have hypothesized that this warming is accompanied by a precipitation increase, as would be expected from the Clausius–Clapeyron relationship, compensating for some of the melt-induced mass loss throughout the western GrIS. This study tests that hypothesis by calculating snow accumulation rates and trends across the western GrIS percolation zone, providing new accumulation rate estimates in regions with sparse in situ data or data that do not span the recent accelerating surface melt. We present accumulation records from sixteen 22–32 m long firn cores and 4436 km of ground-penetrating radar, covering the past 20–60 years of accumulation, collected across the western GrIS percolation zone as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Trends from both radar and firn cores, as well as commonly used regional climate models, show decreasing accumulation rates of 2.4±1.5 % a−1 over the 1996–2016 period, which we attribute to shifting storm tracks related to stronger atmospheric summer blocking over Greenland. Changes in atmospheric circulation over the past 20 years, specifically anomalously strong summertime blocking, have reduced GrIS surface mass balance through both an increase in surface melting and a decrease in accumulation rates.

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Outlet glacier dynamics and bathymetry at Upernavik Isstrøm and Upernavik Isfjord, North-West Greenland

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/geusb.v31.4668 ◽

1969 ◽

Vol 31 ◽

pp. 79-82 ◽

Cited By ~ 7

Author(s):

Camilla S. Andresen ◽

Kristian K. Kjeldsen ◽

Benjamin Harden ◽

Niels Nørgaard-Pedersen ◽

Kurt H. Kjær

Keyword(s):

Mass Loss ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Outlet Glacier ◽

North West ◽

The Past ◽

The North ◽

Glacier Dynamics ◽

Global Sea Level ◽

North Western

During the past decades, the Greenland ice sheet has experienced a marked increase in mass loss resulting in an increased contribution to global sea-level rise. The three largest outlet glaciers in Greenland have increased their discharge, accelerated, thinned and retreated between 1996 and 2005. After 2005 most of them have slowed down again although not to previous levels. Geodetic observations suggest that rapid increase in mass loss from the north-western part of the ice sheet occurred during 2005–2010 (Kjeldsen et al. 2013).

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Monitoring Changes in the Transparency of the Largest Reservoir in Eastern China in the Past Decade, 2013–2020

Remote Sensing ◽

10.3390/rs13132570 ◽

2021 ◽

Vol 13 (13) ◽

pp. 2570

Author(s):

Teng Li ◽

Bozhong Zhu ◽

Fei Cao ◽

Hao Sun ◽

Xianqiang He ◽

...

Keyword(s):

Remote Sensing ◽

Mean Squared Error ◽

Eastern China ◽

Water Environment ◽

Relative Difference ◽

Boreal Summer ◽

Support Vector ◽

Lake Area ◽

The Past ◽

Remote Sensing Reflectance

Based on characteristics analysis about remote sensing reflectance, the Secchi Disk Depth (SDD) in the Qiandao Lake was predicted from the Landsat8/OLI data, and its changing rates on a pixel-by-pixel scale were obtained from satellite remote sensing for the first time. Using 114 matchups data pairs during 2013–2019, the SDD satellite algorithms suitable for the Qiandao Lake were obtained through both the linear regression and machine learning (Support Vector Machine) methods, with remote sensing reflectance (Rrs) at different OLI bands and the ratio of Rrs (Band3) to Rrs (Band2) as model input parameters. Compared with field observations, the mean absolute relative difference and root mean squared error of satellite-derived SDD were within 20% and 1.3 m, respectively. Satellite-derived results revealed that SDD in the Qiandao Lake was high in boreal spring and winter, and reached the lowest in boreal summer, with the annual mean value of about 5 m. Spatially, high SDD was mainly concentrated in the southeast lake area (up to 13 m) close to the dam. The edge and runoff area of the lake were less transparent, with an SDD of less than 4 m. In the past decade (2013–2020), 5.32% of Qiandao Lake witnessed significant (p < 0.05) transparency change: 4.42% raised with a rate of about 0.11 m/year and 0.9% varied with a rate of about −0.09 m/year. Besides, the findings presented here suggested that heavy rainfall would have a continuous impact on the Qiandao Lake SDD. Our research could promote the applications of land observation satellites (such as the Landsat series) in water environment monitoring in inland reservoirs.

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Long Short-Term Memory Networks for Pattern Recognition of Synthetical Complete Earthquake Catalog

Sustainability ◽

10.3390/su13094905 ◽

2021 ◽

Vol 13 (9) ◽

pp. 4905

Author(s):

Chen Cao ◽

Xiangbin Wu ◽

Lizhi Yang ◽

Qian Zhang ◽

Xianying Wang ◽

...

Keyword(s):

Pattern Recognition ◽

Short Term Memory ◽

Three Dimensional ◽

Earthquake Risk ◽

Earthquake Activity ◽

Earthquake Catalog ◽

Short Term ◽

Term Memory ◽

Earthquake Migration ◽

Long Short Term Memory

Exploring the spatiotemporal distribution of earthquake activity, especially earthquake migration of fault systems, can greatly to understand the basic mechanics of earthquakes and the assessment of earthquake risk. By establishing a three-dimensional strike-slip fault model, to derive the stress response and fault slip along the fault under regional stress conditions. Our study helps to create a long-term, complete earthquake catalog. We modelled Long-Short Term Memory (LSTM) networks for pattern recognition of the synthetical earthquake catalog. The performance of the models was compared using the mean-square error (MSE). Our results showed clearly the application of LSTM showed a meaningful result of 0.08% in the MSE values. Our best model can predict the time and magnitude of the earthquakes with a magnitude greater than Mw = 6.5 with a similar clustering period. These results showed conclusively that applying LSTM in a spatiotemporal series prediction provides a potential application in the study of earthquake mechanics and forecasting of major earthquake events.

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New models for the rapid evolution of the central star of the Stingray Nebula

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab890 ◽

2021 ◽

Author(s):

T M Lawlor

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Planetary Nebula ◽

Rapid Evolution ◽

Central Star ◽

Asymptotic Giant Branch ◽

Initial Mass ◽

Thermal Pulse ◽

The Past ◽

New Models

Abstract We present stellar evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase for models of initial mass 1.2 M⊙ and 2.0 M⊙ that experience a Late Thermal Pulse (LTP), a helium shell flash that occurs following the AGB and causes a rapid looping evolution between the AGB and PN phase. We use these models to make comparisons to the central star of the Stingray Nebula, V839 Ara (SAO 244567). The central star has been observed to be rapidly evolving (heating) over the last 50 to 60 years and rapidly dimming over the past 20–30 years. It has been reported to belong to the youngest known planetary nebula, now rapidly fading in brightness. In this paper we show that the observed timescales, sudden dimming, and increasing Log(g), can all be explained by LTP models of a specific variety. We provide a possible explanation for the nebular ionization, the 1980’s sudden mass loss episode, the sudden decline in mass loss, and the nebular recombination and fading.

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