Some of the ideas discussed in this blog are published in my new book called "The Stonehenge Bluestones" -- due for publication on June 1st 2018. After that, it will be available by post and through good bookshops everywhere. Bad bookshops might not have it....
To order, click

Sunday, 15 July 2012

Danger -- ice at work

This spectacular high-definition photo shows the moment of impact when a huge boulder slides down the steep face of an ice-cored moraine into an ice-dammed or marginal lake.  This was taken on the flank of the Unterer Grindelwaldgletscher in the Alps, in May 2009.  The ice cored moraine face was 240m high, and during this collapse alone, 300,000 tonnes of debris collapsed into the lake, with high and destrucive waves causing a rearrangement of the outlines of the lake.  Lakes such as this can also drain catastrophically, and geomorphologists have learned that such environments, with deep and turbulent water, high glacier melt rates, and steep slopes of ice cored moraines are extremely dangerous.  People who walk on the crests of these ice cored moraines are putting themselves into danger -- and people (often unsuspecting tourists) are killed every year by collapses such as this.

Sometimes one has no option but to walk across such terrain, as my colleagues and I had to do in East Greenland in 1962, with very heavy packs on our backs.  Having crossed a wasting glacier and reached the safety of "solid ground" on the other side, there is just one emotion -- relief.....

This is another environment you definitely want to stay clear of..... hanging glaciers on the high flank of Mount Cook, South Island of New Zealand.  Features such as these are caused by very high snow accumulation rates and where friction on the rough bedrock surface is sufficient (for a while) to retain these enormous weights of snow and firn in position.  Some of these strange little glaciers may survive for decades, but many are very short lived, and during a warm summer, meltwater on the ice-rock interface may be sufficient to overcome the frictional drag -- resulting in a catastrophic collapse.  So avalanches are inevitable on slopes such as these.  Nevertheless, people still climb on them and ski on them in the spring, and people still get killed every year.......

These photos come from the great "Glaciers Online" web site.

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