Glaciers & Ice: How They Form & Where to See Them

A glacier forms where more snow falls in winter than melts in summer, year after year, until the accumulated weight compresses the lower layers into ice. Once the mass is roughly 30 m thick, it begins to deform and flow under its own weight. That flow is what makes glaciers geological agents rather than just frozen water: they quarry rock, carve valleys into U-shapes and deposit the debris as moraine.

How glaciers & ice form

The mechanism, without the jargon.

1. 01Snow accumulates and compresses, first to firn and then to dense glacial ice, over decades to millennia.
2. 02Once the mass is thick enough, the ice deforms plastically and begins flowing downhill under gravity.
3. 03Meltwater at the base acts as a lubricant and lets the glacier slide, which dramatically increases erosion.
4. 04Ablation — melting and calving at the lower end — balances accumulation; when ablation wins, the glacier retreats.

Best time to see them

For walking on glaciers, the local summer: June to August in the northern hemisphere, November to March in Patagonia. For ice caves, midwinter to early spring, when the meltwater channels are frozen open and stable enough to enter.

How to get there

Never walk onto a glacier without a guide, a harness, crampons and a rope team unless you have been trained. Crevasses are frequently bridged by snow that gives way without warning. Ice caves require a guide for the same reason, plus helmets.

Tickets, permits & fees

Glacier viewpoints on public land are generally free. Guided glacier walks, ice cave tours and ice climbing are priced as guided activities and usually include equipment. Some glaciers require a national park or conservation area fee on top.

Notable glaciers & ice

Five worth building a trip around.

• Vatnajökull ice caves

  Iceland

  Meltwater carves cathedral-like blue caves under Europe's largest ice cap each summer; they are only stable enough to enter in winter.

  November–March Guide

• Blood Falls

  Antarctica

  A rust-red brine outflow from beneath the Taylor Glacier, fed by a subglacial pocket of salt water isolated for over a million years.

  November–February Guide

• Perito Moreno

  Argentina

  One of the few glaciers that is not retreating, and one of the few where you can watch house-sized ice blocks calve from a boardwalk.

  November–March

• Jostedalsbreen

  Norway

  The largest glacier in continental Europe, with arms reaching down into green valleys at surprisingly low altitude.

  June–September

• Fox and Franz Josef

  New Zealand

  Glaciers that descend into temperate rainforest — an almost unique combination of ice and jungle in the same valley.

  November–March

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