EPOW - Ecology Picture of the Week

Portage Glacier, calved iceberg, and Portage Lake
Southeast Alaska, August 1975

Explanation:  Now you see it ... This is a peek in to the past, at a disappearing glacier in southeast Alaska.  

The year is 1975, and my sister and I had just ridden our motorcycles from California to Alaska.  We are visiting Portage Glacier, and on this cool August day the clouds parted to avail us of a view of the icefield pouring from its mountain source into the meltwater before us.  Large icebergs floated serenely, calved from the glacial face that was still a good 3 miles across the lake, to give you a sense of scale.

And today?  Today, this view has radically changed.  The glacier has ... well, disappeared from view ... melting back so far that it is no longer visible from this vantage point.  Compare this week's EPOW photo with this one taken from the same location in 2002!

The so-called firn line -- the highest point on the glacier where snow melts -- has been migrating uphill over the years.   This means that, over time, a greater and greater proportion of the glacier is melting -- that is, its zone of ablation (its melting zone) has been rising.   Although geologists speak of glacial retreat, this doesn't mean that the ice flows uphill; it simply refers to increased melting over freezing, so that, like a snowman sitting on a hot grate, it shrinks even though there may still be winter snow falling on it.  

Is this a new phenomenon for this glacier?  Apparently not; Portage Glacier  has been retreating at least since 1914 and even earlier when records first started.  Its recession can be traced to climate warming following the Little Ice Age (mid-19th century).  But whether or not human industrial activity and associated increases of greenhouse gases caused this warming and melting trend, they likely are exacerbating the situation, and glaciers worldwide are feeling the heat.