Like other high-latitude locations on Earth, glaciers in Iceland have advanced and retreated many times during the past 2.5 million years, since we’ve been in a global Ice Age. The last glacial maximum was about 20,000 years ago, when ice completely covered the island and extended up to 200 km (120 miles) beyond the coastline to cover the marine shelf. Since then, glaciers have retreated at a rapid rate, especially during the past decades as climate change has accelerated.
Iceland has changed much since the last glacial maximum when ice covered the island and extended far offshore. At that time, all of the island’s volcanoes would have been under ice. As the ice has melted, the island has been uplifted by a process called glacial rebound. Imagine putting the weight of your finger on an ice cube in your glass. When you release your finger, the ice cube moves upward in response. Similarly, Earth’s crust gets depressed by the weight of ice, and rises upward (rebounds) as the ice load melts. The uplift rate from glacial rebound along the southern edge of Vatnajökull is ~2.5 cm/yr (1 inch/year). The next six photos are from the coast on the southeast side of Vatnajökull.
A fascinating, and potentially terrifying, aspect of Iceland’s glaciers is that they cover active volcanoes. As you can imagine, when a volcano erupts under ice, it causes a lot of melting. This melt water flows outward, sometimes in catastrophic amounts and dangerously high speeds. These glacial outbursts are called jökulhlaups (=glacial run).
Continuing northeast along the edge of Vatnajökull (see map at top of post) are a series of sárlón (=glacial river lagoons) that formed since glaciers have been in rapid retreat. Glacial melt water is trapped behind terminal moraines and, with increased melting, the lagoons continue to expand.
We’ll next go to the north side of the island, near Akureyri (see location on map at the top of the post). On the map, notice the long indentations in the northern shoreline. Like other high-latitude locations during the glacial maximum, glaciers carved valleys that later filled with ocean water when the glaciers melted and sea level rose.
This is my last Iceland post, at least for the July 2022 trip, and so I’ll end with a few photos I like.
Iceland, the formation and evolution of a young, dynamic, volcanic island—a field trip guide: Geological Society of America Field Guide 54, 2019, by Jordan, Carley, and Banik.
Iceland: tectonics, volcanics, and glacial features, 2020, by Tamie Jovanelly.
Iceland, Third Edition (Classic Geology in Europe series), 2022, by Thordarson & Höskuldsson.