Michael Portillo’s Alaskan Glacier

By Paul Homewood

h/t Dave Ward

  

The BBC Thought Police must have missed this one!

 image

https://www.bbc.co.uk/iplayer/episode/b0by7vtg/great-alaskan-and-canadian-railroad-journeys-series-1-1-ninilchik-to-spencer-whistlestop 

The excellent Michael Portillo is back with with his latest railroad journeys, along with his trusty Appleton’s Guidebook.

[For non-UK readers, apologies as usual, as you may not be able to access BBC i-player.

But as a quick background, Portillo has for the last few years been travelling around the world by rail (courtesy of BBC licence payers). He carries with him the Appleton’s Guidebook, which originated for Britain in the mid 19thC, but later went international.

Appleton was effectively a tourist book for intrepid rail travellers in Victorian times. Along with detailed information about the railways themselves, Appleton also included plenty of information about stopovers on route, hotels to stay in, tourist attractions, famous buildings, useful tidbits etc.

Along his routes, Portillo stops off to visit some of the sites mentioned in the guidebook, and talk to local experts]

This latest series is based in Alaska, and, at 23 mins in, Portillo moves into glacier country. He informs us that his Appleton’s Guide for Alaska, which was published in 1899, states:

“Old residents insist that the climate is changing. That the summers are warmer and drier. The rapid retreat of all the glaciers during even 20 years is offered as another proof.”

He goes on to comment that he finds it stunning that the issue of warming is being addressed in the words of our Appleton’s author more than a century ago.

Unfortunately, Portillo does not seem to have connected the dots. That this warming and retreat of the glaciers began long ago in the 19thC, long before humans could have had any effect on climate.

The fact that Alaskan glaciers began receding in the 19thC is well known to scientists, not to mention readers of this blog.

For instance, the US Geological Survey (USGS) published this schematic of the famous Glacier Bay.

glacierbaymap_thumb

https://soundwaves.usgs.gov/2001/07/fieldwork2.html

As we can see, glacier retreat began in the late 18thC, and most of the retreat took place in the 19th and early 20thC.

Michael Portillo is actually stood next to the Portage Lake on the film, near Anchorage, which he tells us was covered by ice in 1899. The history of the Portage Glacier tells a similar tale to Glacier Bay.

The Portage Pass served as a surface transportation route between Upper Cook Inlet and Prince William Sound–prehistorically, for competing interior and coastal native groups, and subsequently for Russian traders and trappers and early miners in the region:

image

image

https://pubs.usgs.gov/fs/2006/3141/

In 1914, the glacier covered all of the Portage Lake, and had rapidly retreated even by 1951.

A study by GR Winkler, Portage Lake and Glacier, published by the Alaska Geological Society in 1984, stated:

For centuries the low pass at the head of Turnagain Arm served as a surface transportation route between Upper Cook Inlet and Prince William Sound–prehistorically, for competing interior and coastal native groups, and subsequently for Russian traders and trappers and early miners in the region. During an early geological reconnaissance of the area, Mendenhall (1900) gave the broad, 600-ft divide the name Portage Pass. During the past 200 years, Portage Glacier has advanced and retreated markedly. According to reports from the Vancouver expedition, in 1794 the glacier did not occupy the valley below the pass, but Portage Lake may have been larger than it is today. The glacier then advanced strongly at least 5 km until about 1890, at which time Portage Pass and the lake basin were completely occupied by ice. The low rubbly mounds which impound present Portage Lake are remnants of the terminal moraine left by this advance. In 1898, gold rush prospectors used the pass by climbing over Portage Glacier.

The approximately 4-km retreat of the glacier since at least 1914 has been documented by Barnes (1943) and Schmidt (1961) and apparently continues today, leaving 190-m deep Portage Lake in the glacial depression

http://archives.datapages.com/data/alaska/data/008/008001/24_akgs0080024.htm

 

Note that in 1890 the glacier covered not only the lake, but also Portage Pass. The pass can be seen on the map below, to the NW of Portage lake, where the Alaska Railroad runs:

 

image

https://pubs.er.usgs.gov/publication/ha583

 

The fact that the pass too was “completely occupied by ice” in 1890 gives some indication of how far the glacier retreated between 1890 and 1914.

Note also the comment that the glacier advanced by 5km after 1794. That is a similar distance to the current length of the lake, so by 1890 the glacier must have been well down the valley leading to Turnagain Arm, where the town of Portage now is.

 

 

The USGS Factsheet, written in 2006, has this history of the glacier:

During the late 1800s and early 1900s, Portage Glacier terminated on land at the western end of Portage Lake, filling Portage Lake with ice (Photo Plate 1914). Since the early 1900s, the glacier has receded, leaving Portage Lake in the scoured basin. The initial retreat of the glacier coincides with known climate warming associated with the end of the Little Ice Age (circa mid-19th century). As the glacier receded, its land-based terminus retreated into proglacial Portage Lake and changed from its relatively stable land-based environment to an unstable calving environment. The most rapid recession of some 140 to 160 meters per year occurred between 1939 (Photo Plate, 1939) and 1950, when water depth at the terminus was at its maximum—roughly 200 meters. Recession continued through the 1970s and 1980s (Photo Plate, 1972, 1984) until by late 1999, Portage Glacier had receded almost 5 kilometers, to a more stable position at the eastern end of Portage Lake (Photo Plate, 1999). The retreat was driven primarily by calving of unstable ice at the glacier terminus into Portage Lake. Ice loss resulting from increased melting of the glacier surface during the past century-long general warming trend contributed to glacier retreat, but to a lesser extent. Today, the terminus of Portage Glacier remains close to its 1999 location.

https://pubs.usgs.gov/fs/2006/3141/ 

Note that the most rapid recession took place prior to 1950. Glacier retreat since then has largely been due to calving of unstable ice, rather than climatic warming.

 

Many scientists have closely measured and studied glaciers throughout Alaska, and the conclusions have always been the same. Alaskan glaciers, which grew enormously during the Little Ice Age, began rapid retreat during the 19thC.

But it is fascinating that this was all common knowledge to a writer of a tourist guidebook published in 1899.

via NOT A LOT OF PEOPLE KNOW THAT

http://bit.ly/2RlC7q3

January 10, 2019 at 01:00PM

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