A massive 'megatsunami' wave created when part of an Alaskan mountain crumbled into the sea is the second tallest ever recorded – and a reminder of the risks posed by melting glaciers, say scientists.

Last summer a giant wave swept through a remote fjord in southeast Alaska leaving destruction in its wake.

The event went largely unreported at the time, but a new scientific analysis shows tiny earthquakes triggered a massive landslide.

An incredible 64 million cubic metres of rock – the equivalent of 24 Great Pyramids - splashed into the water below. The sheer power of that amount of rock plunging into the fjord in under a minute created a gigantic wave almost 500 metres tall.

Only the time it happened – in the early hours of the morning – prevented tourist cruise ships being caught up in the devastation, say the researchers.