Isostatic Rebound

Isostatic Rebound (Post-Glacial Rebound) is the term used to describe the ‘springing back’ of the Earth’s crust following deglaciation. Even today, many thousands of years after the last Ice Age we can detect this ‘rebound’ continuing. In parts of North America, this has been measured at up to half an inch per year although this must be seen as somewhat exceptional. After the last Ice Age, parts of what is now southern and western Finland were under water but as the crust began to rise land rose above sea level and is still doing so today. Since the rate of rebound is known, archaeologists have been able to use the process to date prehistoric sites in the region. There are a number of useful websites that explain the process^(a)(b).

Glacier Bay (Alaska) and the surrounding area show the fastest rates of isostatic uplift on the planet. An uplift of about 5.5 meters has taken place in Glacier Bay since the retreat of glacial ice beginning about 250 years ago. Uplift should continue for several hundred more years^(c).

A comparable situation is also found in the Hudson Bay region which had some of the heaviest glacial ice during the last Ice Age and was the final area to have the ice melt away. The land surface there is rising more than a half-inch per year — more than 4 feet per century^(d).

Another example of this rebound was recently (June 2024) mentioned in a BBC article in relation to the Finnish island of Maakalla.  It revealed that ” when the island was discovered [by fishermen and seal hunters in the 15th Century], it was only 9mm above the water’s surface,” explained Matti Hautala, the boat captain who ferried us here from Keskuskari harbour on the mainland. Everything around me was once submerged under water, but each year since the weight of Ice Age glaciers that once covered this area melted more than 10,000 years ago, the land holding Bothnian Bay continues to slowly rise – a phenomenon known as glacio-isostatic uplift. Today, the island is more than 5m above sea level^(e).

^(a) https://web.archive.org/web/20191102194637/https://academic.emporia.edu/aberjame/ice/lec09/lec9.htm

^(b) https://www.antarcticglaciers.org/glaciers-and-climate/sea-level-rise-2/recovering-from-an-ice-age/

^(c) https://scitechc.com/faq/what-is-isostatic-rebound-in-glacier-geology/

^(d) https://eu.freep.com/story/news/local/michigan/2018/03/02/michigan-great-lakes-ice-age/363316002/

^(e) https://www.bbc.com/travel/article/20240624-maakalla-europes-isolated-autonomous-island *