When do glaciers calve in alaska

Doug Benn and colleagues in the journal Earth Science Reviews. If you want to know more about glacier calving, this review paper would make a great starting point. Calving is the glaciological term for the mechanical loss or simply, breaking off of ice from a glacier margin 1.

Calving is most common when a glacier flows into water i. Photo: Liam Quinn. In lake-terminating or freshwater glaciers, calving is often a very efficient process of ablation and is therefore an important control on glacier mass balance Calving is also important for glacier dynamics and ice retreat rates 1. Calving glaciers are often highly dynamic, with patterns of behaviour e. Compared to marine-terminating or tidewater glaciers, like those at the margins of the Antarctic and Greenland ice sheets, freshwater glaciers are normally smaller and slower moving.

This means that while the processes of calving can be very similar in both settings, freshwater glaciers tend to have lower calving rates 1. Before calving occurs, smaller cracks and fractures in glacier ice grow or propagate into larger crevasses see image below.

The growth of crevasses effectively divides the ice into blocks that subsequently fall from the snout into an adjacent lake where they are known as icebergs. Therefore, the fracture of ice is an important control on: where calving will occur, the size of calved icebergs, and how often calving events happen 1.

Photo: Wojciech Strzelecki. Cracks and fractures in glacier ice will grow when the stress acting on a fracture is larger than the fracture strength of ice 8. When this condition is met, the ice will fracture in a brittle fashion, causing existing cracks to become deeper and wider. Large stresses occur in many situations in glaciers. Example of large fractures in the snout of Goldbergkees Gletscher in the Austrian Alps. Photo: Ewald Gabardi.

Water plays a key role in the depth of crevasses and the likelihood of calving see diagram below. In a water-free crevasse, stress at the crevasse tip is offset by the weight of overlying ice.

This causes a fracture to close up. However, in a water-filled crevasse, the pressure of water offsets the weight of ice. This allows a crevasse to extend deeper into the ice, and often to the glacier bed 8. In a water free crevasse, the weight of ice forces the fracture shut. In a water-filled crevasse, by contrast, the added water pressure counteracts the weight of ice, allowing a fracture to deepen. There are several main calving mechanisms at freshwater glaciers, all of which are related to stress at the glacier terminus 1.

At a grounded lake-terminating glacier, ice flow commonly becomes faster due to basal sliding near the snout. The rate of glacial ice loss can change abruptly and unpredictably, and Bartholomaus wanted to know why. Tidewater glaciers—glaciers that end in the ocean—are some of the fastest-changing glaciers on Earth.

To better understand why glaciers calve, seismologists are examining seismic signals produced by icequakes. The recent transition of the Transportable Array to southern Alaska may help further our understanding of icequakes and their connection to ice loss and sea level rise.

The team first wanted to know when calving was happening at the edge of the glacier so that he could match the seismic waves to the size of the fallen ice chunk. Then they considered environmental factors including rainfall, wind, and temperatures, that might correspond to times when the glacier crumbled most.

Seismologists are using these seismic signals to determine when and why calving occurs Photo by Tim Bartholomaus. While the team did visit the glacier, they primarily turned to records of seismicity generated by the ice shaking during icequakes.

Water engulfs the block, creating an air pocket above it. The seismic waves from icequakes have a signature distinct from those from earthquakes. Local magnitudes are typically near 1. They are mostly surface waves that seem to travel through the ice, over the surface, and through shallow crust, and are detected by recording stations hundreds of kilometers away.

They could readily detect the frequency of calving events, but the team was interested in more than just when icequakes occur. Ultimately, Bartholomaus and his colleagues wanted to know just how much ice is lost in a particular time period—they needed a way to use the icequake data to estimate the size of the ice block that falls into the water.

They started out the old-fashioned way, traveling to Icy Bay and watching, in person, thousands of calving events at Yahtse Glacier over 12 days in June They noted each instance of falling ice and matched it with the records from the seismometers. For each event, they visually estimated the iceberg size by lumping it into one of seven size classes, which ranged from chunks smaller than 30 feet on one side to foot-wide sheets that spanned the entire height of the glacier, at almost feet.

Joy Sheehan from A Jaunt With Joy, explains that for all the different glaciers in Alaska, each has its own individual best way to view it. Hubbard Glacier is best viewed from a balcony cabin on a cruise ship, which allows you to get up close and personal with the face of the glacier. It beats having to bundle up into warm clothing and join all the other passengers squished together on the open deck.

Here are some of the essential items you need to pack:. Polarized sunglasses will also be useful as looking around the water can cause glare and these types of sunglasses will remove this. By Becky. Please help us make your emails more personalised by filling in these extra details. Rest assured that your privacy is important to us and your details will not be shared with any 3rd party marketing companies.

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Unmissable glaciers Mendenhall Glacier Some glaciers can be accessed by the road and just outside of Juneau is Mendenhall Glacier, which attracts more than , visitors every year. Glacier Bay Glacier Bay is so spectacular that most cruise ships will spend most of the day there.