I think many of us have heard various estimates of the thickness of the glacier but what were the methods used and which are the most reliable.
Hi Ken, I am only goiing on what I was told me at Boston University. Hopefully, here will be a good response that I can participate in. Thank you. Paul.
I cannot answer for the local evaluation, but from the three different reconstructions for the full Laurentide ice-sheet, we are talking about two kilometers in surface elevation (that is about 1/3 additional in thickness), depending on the precise location. cf. for example discussion of the reconstruction at
https://wiki.lsce.ipsl.fr/pmip3/doku.php/pmip3:design:pi:final:icesheet
and the hemispheric plots at the bottom of the page:
https://wiki.lsce.ipsl.fr/pmip3/lib/exe/fetch.php/pmip3:design:21k:icesheet:gnh5.pdf
Full references to adequate publications are given on the same page.
All the best,
Hi Didier, I think that your estimate is probably a good one, but I dont quite understand "about 1/3 additional in thickness"
Does anyone know the amount of glacial rebound in New England over the last 10,000 yr?
The density of rock is about 2.0 and ice 1.0 so a 2 km layer of ice will cause an isostatic depression of 1 km.
I fully agree with Alastair: this is exactly why I said previously that if you know the additional elevation (in that case ~2 km), the total thickness is then 3 km [of which 1 km of depression of the continent surface = 1/3]. In gross numbers.
Dear Didier, Thanks very much for the clarification. Much appreciated. Paul.
"New England" is a significant area and "Wisconsin" a significant time span! The maximum southern extent extent of Laurentide ice is defined by Long Island, Martha's Vinyard/Nantucket, and George's Bank, thus the ice thickness along the present coastline would have been a few hundred meters at most. In early stages of ice sheet growth, cirque glaciers in the White Mountains and at Mt Katahdin would have been a few tens of meters thick. In contrast, at maximum, Hitchcock (1876) reported till, erratics, and striations on the summit of Mt. Washington, thus two km is a minimum ice surface elevation there. Equilibrium ice profile models would suggest three km as a closer estimate, with the ice surface rising, thus thickness increasing, towards the St Lawrence.
Isostatic rebound, although present, is unlikely to provide a reasonable estimate for ice thickness as it would require an equilibrium ice sheet to persist for tens of thousands of years in order to allow for compensation. Where ages have been defined around the ice margin, the maximum extent appears to have lasted for only thousands or even hundreds of years.
Dear William,
Your estimate of 3 km for the thickness of the ice sheet in New England is quite reasonable as is your logic. i vote you up on your answer. Best wishes, Paul.
Good answers. How do you account for all of the rocks and boulders that dot and fill hill and dale throughout New Hampshire and Vermont?
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts