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Author Topic: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe  (Read 118650 times)

jai mitchell

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #250 on: November 21, 2017, 04:22:15 PM »
Article today that discusses the implication of wise et al. described above by ASLR and the previous DeConto paper describing Thwaites and PIG SLR potentials.

https://grist.org/article/antarctica-doomsday-glaciers-could-flood-coastal-cities/
Doomsday on Ice

Rapid collapse of Antarctic glaciers could flood coastal cities by the end of this century.

By Eric Holthaus   on Nov 21, 2017

Quote
The only place in the world where you can see ice-cliff instability in action today is at Jakobshavn glacier in Greenland, one of the fastest-collapsing glaciers in the world. DeConto says that to construct their model, they took the collapse rate of Jakobshavn, cut it in half to be extra conservative, then applied it to Thwaites and Pine Island.
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #251 on: November 23, 2017, 11:04:43 AM »
Perhaps current basal roughness reflects past cliff fracturing with shallow bergs and little bed erosion. If so, rough beds may be a sign of rapid glacial retreat.

I concur with your hypothesis.
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #252 on: December 01, 2017, 04:39:04 AM »
The linked article is a nice summary for anyone new to this topic (the two attached images from the article show the cumulative ice mass loss from 1980 to 2016 for the PIG and the Thwaites Glacier, respectively):

Title: "In Antarctica, Two Crucial Glaciers  Accelerate Toward the Sea"

https://www.nytimes.com/interactive/2017/10/26/climate/antarctica-glaciers-melt.html

(Hint for those who want to learn more, no one knows more about these two glaciers than Eric Rignot)
« Last Edit: December 01, 2017, 10:10:31 PM by AbruptSLR »
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #253 on: December 07, 2017, 05:31:51 PM »
The linked reference indicates that ice shelf melt rates in the ASE requires complex modeling but indicates that this issue will likely contribute to an acceleration of grounding line retreats for both PIG and Thwaites, in coming decades:

Marion Donat-Magnin et al. (6 December 2017), "Ice-Shelf Melt Response to Changing Winds and Glacier Dynamics in the Amundsen Sea Sector, Antarctica", JGR Oceans, DOI: 10.1002/2017JC013059

http://onlinelibrary.wiley.com/doi/10.1002/2017JC013059/abstract?utm_content=buffer9d542&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "It has been suggested that the coastal Southern Ocean subsurface may warm over the 21st century in response to strengthening and poleward shifting winds, with potential adverse effects on West Antarctic glaciers. However, using a 1/12° ocean regional model that includes ice-shelf cavities, we find a more complex response to changing winds in the Amundsen Sea. Simulated offshore subsurface waters get colder under strengthened and poleward shifted winds representative of the SAM projected trend. The buoyancy-driven circulation induced by ice-shelf melt transports this cold offshore anomaly onto the continental shelf, leading to cooling and decreased melt below 450 m. In the vicinity of ice-shelf fronts, Ekman pumping contributes to raise the isotherms in response to changing winds. This effect overwhelms the horizontal transport of colder offshore waters at intermediate depths (between 200 and 450 m), and therefore increases melt rates in the upper part of the ice-shelf cavities, which reinforces the buoyancy-driven circulation and further contributes to raise the isotherms. Then, prescribing an extreme grounding line retreat projected for 2100, the total melt rates simulated underneath Thwaites and Pine Island are multiplied by 2.5. Such increase is explained by a larger ocean/ice interface exposed to CDW, which is then amplified by a stronger melt-induced circulation along the ice draft. Our main conclusions are that (1) outputs from ocean models that do not represent ice shelf cavities (e.g. CMIP5 models) should not be directly used to predict the thermal forcing of future ice shelf cavities; (2) coupled ocean/ice sheet models with a velocity-dependent melt formulation are needed for future projections of glaciers experiencing a significant grounding line retreat."
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #254 on: January 22, 2018, 11:01:37 PM »
The linked reference finds that with regards to ice mass loss from the BSB that: " Grounding line retreats that begin faster proceed more rapidly because the shorter time interval for the grounding line to erode into the grounded ice sheet means relatively thicker ice and larger driving stress upstream of the boundary."  This indicates that it is a very bad idea to continue following a BAU forcing pathway as mankind has been doing since the pre-industrial era.

M. S. Waibel, C. L. Hulbe, C. S. Jackson & D. F. Martin (16 January 2018), "Rate of mass loss across the instability threshold for Thwaites Glacier determines rate of mass loss for entire basin", Geophysical Research Letters, DOI: 10.1002/2017GL076470

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076470/abstract?utm_content=buffer0799e&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Rapid change now underway on Thwaites Glacier (TG) raises concern that a threshold for unstoppable grounding line retreat has been or is about to be crossed. We use a high-resolution ice sheet model to examine the mechanics of TG self-sustained retreat by nudging the grounding line just past the point of instability. We find that by modifying surface slope in the region of the grounding line, the rate of the forcing dictates the rate of retreat, even after the external forcing is removed. Grounding line retreats that begin faster proceed more rapidly because the shorter time interval for the grounding line to erode into the grounded ice sheet means relatively thicker ice and larger driving stress upstream of the boundary. Retreat is sensitive to short-duration re-advances associated with reduced external forcing where the bathymetry allows re-grounding, even when an instability is invoked."
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wili

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #255 on: January 23, 2018, 03:38:36 AM »
"Rapid change now underway on Thwaites Glacier (TG) raises concern that a threshold for unstoppable grounding line retreat has been or is about to be crossed"

I hadn't heard it put quite that way in writing in the scientific literature yet, but I obviously have not been paying close enough attention.

This sounds kind of...bad...
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #256 on: January 23, 2018, 03:55:24 AM »
"Rapid change now underway on Thwaites Glacier (TG) raises concern that a threshold for unstoppable grounding line retreat has been or is about to be crossed"

I hadn't heard it put quite that way in writing in the scientific literature yet, but I obviously have not been paying close enough attention.

This sounds kind of...bad...

I would have thought that the "Ice Apocalypse" thread would have given some idea of how much at risk that the TG is of crossing a threshold:

https://forum.arctic-sea-ice.net/index.php/topic,2205.0.html

However, if that thread is not sufficient I re-post the following from the Potential Collapse Scenario for the WAIS" thread

"Based on my interpretation of the two linked references, I suspect that local ice cliff failures near the base of the Thwaites Ice Tongue (see the four images) will begin sometime 2025 and 2033, and will be initiated due to influences from Super El Nino events in that timeframe:

Yu, H., Rignot, E., Morlighem, M., & Seroussi, H. (2017). Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics. The Cryosphere, 11(3), 1283, doi:10.5194/tc-11-1283-2017

https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017.pdf
https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017-assets.html

Abstract. "Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades.  Here, we present a study of its calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing.  We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that are consistent with the distribution of depth and width of surface and bottom crevasses observed by NASA’s Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate crevasses that are consistent with observations.  We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of calving events. It is more prominent for glaciers with rapid calving rates than for glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining crevasse formation and iceberg calving."

Extract: "In our simulations, we find that crevasses propagate significantly faster near the ice front when the ice shelf is shortened.

The reason for the propagation of crevasses is the existence of a nonhydrostatic condition of ice immediately downstream of the grounding line, which is not accounted for in simplified models that assume hydrostatic equilibrium everywhere on the ice shelf.  We also find that calving is enhanced in the presence of pre-existing surface crevasses or shorter ice shelves or when the ice front is undercut.  We conclude that it is important to consider the full stress regime of ice in the grounding line region to replicate the conditions conducive to calving events, especially the nonhydrostatic condition that is critical to propagate the crevasses."

&

The second linked reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of extreme El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent.""
« Last Edit: January 23, 2018, 09:20:33 PM by AbruptSLR »
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wili

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #257 on: January 23, 2018, 04:49:31 AM »
Thanks for the added info, ASLR.
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Sigmetnow

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #258 on: January 24, 2018, 04:47:58 PM »
“Looking at these two glaciers as a system involved a time-consuming process of building algorithms that interpret airborne data gathered from planes flying at different heights with unique radar systems.”

Stanford researcher: Interacting Antarctic glaciers may cause faster melt and sea level contributions
Quote
A new study shows that a large and potentially unstable Antarctic glacier may be melting farther inland than previously thought and that this melting could affect the stability of another large glacier nearby – an important finding for understanding and projecting ice sheet contributions to sea-level rise.

The findings, by a Stanford-led team of radar engineers and geophysical glaciologists, came from radar data collected at the same locations in 2004, 2012 and 2014, each revealing details of the glaciers miles below the surface. The surveys show that ocean water is reaching beneath the edge of the Pine Island Glacier about 7.5 miles further inland than indicated by previous observations from space.

The team also found that the Southwest Tributary of Pine Island Glacier, a deep ice channel between the two glaciers, could trigger or accelerate ice loss in Thwaites Glacier if the observed melting of Pine Island Glacier by warm ocean water continues down the ice channel. The results were published online in the Annals of Glaciology. ...
https://earth.stanford.edu/news/stanford-researcher-interacting-antarctic-glaciers-may-cause-faster-melt-and-sea-level
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #259 on: February 23, 2018, 06:05:02 PM »
For the sake of completeness, I provide the linked reference, which considers possible interactions between the PIG and Thwaites glacier:

Dustin M. Schroeder et al. Ocean access beneath the southwest tributary of Pine Island Glacier, West Antarctica, Annals of Glaciology (2017). DOI: 10.1017/aog.2017.45

https://www.cambridge.org/core/journals/annals-of-glaciology/article/ocean-access-beneath-the-southwest-tributary-of-pine-island-glacier-west-antarctica/EFF449338C7D7D088CCB7BC48D40B150

Abstract: "The catchments of Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are two of the largest, most rapidly changing, and potentially unstable sectors of the West Antarctic Ice Sheet. They are also neighboring outlets, separated by the topographically unconfined eastern shear margin of Thwaites Glacier and the southwest tributary of Pine Island Glacier. This tributary begins just downstream of the eastern shear margin and flows into the Pine Island ice shelf. As a result, it is a potential locus of interaction between the two glaciers and could result in cross-catchment feedback during the retreat of either. Here, we analyze relative basal reflectivity profiles from three radar sounding survey lines collected using the UTIG HiCARS radar system in 2004 and CReSIS MCoRDS radar system in 2012 and 2014 to investigate the extent and character of ocean access beneath the southwest tributary. These profiles provide evidence of ocean access ~12 km inland of the 1992–2011 InSAR-derived grounding line by 2014, suggesting either retreat since 2011 or the intrusion of ocean water kilometers inland of the grounding line."
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #260 on: April 27, 2018, 07:35:08 PM »
The two attached Sentinel1 images from April 27 & 26, respectively, make it very clear that as the Pine Island Ice Sheet flows, it will soon break-off a large portion of the Southwest Tributary Ice Shelf.  This will reduce the buttressing action of the Southwest Tributary Ice Shelf on the Southwest Tributary Glacier; which in-turn will reduce the shear stress on Thwaites Glacier's eastern shear margin (which will reduce the stability of Thwaites).

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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #261 on: May 14, 2018, 07:32:05 PM »
The first attached Sentinel-1 image of the SW Tributary Ice Shelf, from May 14 2018, makes it clear that a major piece of the ice shelf has now become an iceberg and that the ice shelf upstream of the iceberg is crumbling to the point that its buttressing action is continuing to degrade.

Edit, the second attached image from Sentinel-1 of the SW Tributary Ice Shelf from June 3 2018, makes it clear that due to the calving of the downstream portion of the shelf, the buttressing from the PIIS on the SW Tributary Ice Shelf has moved in the Northwest direction, which in my opinion will contribute to the calving upstream for future PIIS calving events.
« Last Edit: June 04, 2018, 07:36:11 PM by AbruptSLR »
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solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #262 on: July 06, 2018, 12:20:47 AM »
Thwaites is continuing to break up.  I noticed this roller pretty far in. Anyone seen recent grounding line info?
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #263 on: July 09, 2018, 04:40:51 PM »
The attached image of both the SW Tributary Ice Shelf and the PIIS calving front, from July 8 2018, indicates that these ice shelves are progressively degrading:
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AbruptSLR

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #264 on: September 24, 2018, 08:50:20 PM »
The attached image from Sept 24 2018 gives me the impression that: 1) the SW Tributary Glacier ice flow velocity is increasing and that 2) the PIIS may undergo a major calving event this coming austral summer.
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solartim27

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #265 on: November 17, 2018, 07:33:48 PM »
A very small, nothing to worry about calving at Thwaites, of only about 10 miles.
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Stephan

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Re: Hazard Analysis for PIG/Thwaites from 2012 to 2040-2060 Timeframe
« Reply #266 on: December 14, 2018, 05:54:12 PM »
The ice shelf west of the Thwaites ice tongue has lost its tip last week. Eyeballing the area it has lost around 60 km². The remains were rapidly transported to the lower left (W-NW direction). See attached images, the upper one from Dec 05, 2018, the lower one from Dec 13, 2018. Both are from EOSDIS worldview. The black line represents the borders of the ice shelf around 2010.