Iain Stewart’s “Ice”: Glaciers in Earth: The Power of the Planet

“Ice” is the third episode of Earth: The Power of the Planet, the five-part BBC Two series presented by geologist Iain Stewart. First broadcast on 4 December 2007, it follows how frozen water carves valleys, builds ice sheets kilometres thick and calves icebergs into the sea, with a visit to one of the fastest glaciers on Earth in Greenland.

Earth: The Power of the Planet, the BBC series

The series ran on BBC Two from 20 November to 18 December 2007, and the National Geographic Channel showed it in the United States in 2008 as Earth: The Biography. Its five episodes look at the forces that made the planet habitable: “Volcano”, “Atmosphere”, “Ice”, “Oceans” and “Rare Earth”. Stewart’s style is hands-on, and he climbs, abseils and flies to reach the places he explains.

How snow becomes glacier ice

A glacier starts as snow that builds up faster than it melts. Layer by layer, the old snow refreezes into granular névé, then is squeezed by the weight above into denser firn. Over years, and often centuries, the firn compacts into solid glacier ice with very few air bubbles. That clean, dense ice absorbs some red light, which is why deep glacier ice glows blue.

Once the ice is about 30 metres thick it starts to flow, and above about 50 metres it deforms plastically under its own weight. Glaciers also slide on meltwater at their base. Most move around a metre a day, but the fastest outlet glaciers travel tens of metres. The rigid upper 50 metres or so cannot bend, so it cracks into crevasses, usually up to about 46 metres deep.

Jakobshavn Glacier (Sermeq Kujalleq) in Greenland

A highlight of the episode is Greenland’s Jakobshavn Glacier, known in Greenlandic as Sermeq Kujalleq, “the southern glacier”. It flows into the Ilulissat Icefjord near the town of Ilulissat in west Greenland, a UNESCO World Heritage Site since 2004. The glacier drains about 6.5% of the Greenland ice sheet and produces around 10% of the island’s icebergs.

Its speed is extraordinary. For decades the front moved about 20 metres a day. After 1997 it accelerated and thinned sharply, and in 2012 it was flowing more than 17 km a year. The front retreated about 30 km between 1850 and 1964, retreated again until 2015, then re-advanced and thickened for a few years after cooler water reached the fjord in 2016.

Explore more: a documented Greenland calving event; the hidden terrain beneath an ice sheet.

The Greenland and Antarctic ice sheets

An ice sheet is a mass of glacial ice covering more than 50,000 square kilometres, and Earth has two today. According to the National Snow and Ice Data Center, together they hold more than 99% of the planet’s land ice and over 68% of its fresh water.

• Antarctica: about 14 million km², up to about 4.9 km thick, enough ice to raise sea level by about 58 metres if it all melted.
• Greenland: about 1.7 million km², covering roughly 80% of the island, over 3 km thick at most, with about 7.4 metres of sea-level equivalent.

Those numbers put the episode in context. Every calving front and meltwater stream is one small part of a system that links snowfall, ice flow and the level of the world’s oceans. For the latest measurements, the NSIDC publishes regular updates on Greenland and Antarctica.

Iain Stewart, geologist and presenter

Iain Stewart, born in 1964, is Professor of Geoscience Communication at the University of Plymouth, which he joined in 2004. His first BBC appearance was as an expert in the 2002 Horizon film about Helike, the ancient Greek city lost to an earthquake on the Gulf of Corinth. He went on to present Journeys from the Centre of the Earth (2004), Journeys into the Ring of Fire (2006), How Earth Made Us (2010) and Rise of the Continents (2013).

“Ice” remains a clear, visual introduction to how glaciers shape mountains and coastlines. UK schools use clips such as “How glaciers form” in geography lessons on glacial landscapes.

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