The Taku Glacier
What it is and what is going to happen to it
The Taku Glacier is the largest glacier draining the
Juneau Icefield. The Juneau Icefield covers about 1,500 sq. miles
of Alaska and British Columbia, and has dozens of major glaciers
and hundreds of small glaciers. All of these have been retreating
with the exception of the Taku. (And its distributary – the
Hole-in-the-Wall Glacier) It appears that this anomaly of the Taku
Glacier is about to end as the Taku appears to be going into
retreat. The retreat is expected to accelerate rapidly with the
retreat rate likely to become >= 500 feet per year within a few
The following sections will examine:
1) The Taku Glacier and its source – the Juneau
2) A model for tidewater glaciers and how this applies to the
3) The history of the Taku Glacier
4) What is happening now to the Taku Glacier
5) Why the Taku Glacier is going to start retreating at >=
500 ft. per year
1) The Taku Glacier and its
source – the Juneau Icefield
The picture above is a Sept. 1984 Landsat satellite
view of the Juneau Icefield. There are about 38 glaciers that
drain ice from icefield.
These 38 glaciers include the Taku and
Juneau’s major tourist attraction, the Mendenhall. All of these
glaciers have been retreating except the Taku. The Taku has been
advancing even though it shares the same snow and ice source as
the other glaciers. The Taku alone has been advancing – up to now.
A closer look at the Taku will begin to explain this anomaly.
The picture above is a detailed topographic map of
the Juneau Icefield (including the Taku and Mendenhall Glaciers).
The map was generated via http://www.mytopo.com/
A topographic map provides more information than just
a plain satellite view. The topographic map tells us that a large
portion of the Taku Glacier’s surface area is less than 4,000 feet
above sea level. The elevations on a topographic map are more
apparent if we look at a color-coded elevation map.
The source for the above picture is at:
The color-coded map shows that the average elevation
of the Taku Glacier is lower than most of the rest of the
icefield. At this lower average elevation, precipitation is still
mostly snow, but it’s a borderline situation as the slightest
increase in temperature will change this precipitation from mostly
snow to mostly rain. Global warming is providing this incremental
increase in temperature.
If we take a little diversion from the Taku Glacier,
it is rather obvious what global warming is doing to one of
Juneau’s main tourist attractions – the Mendenhall Glacier. The
two pictures below are from the video at https://vimeo.com/69802285
The picture above shows the Mendenhall Glacier as of
1958 as seen from near the current Mendenhall Glacier Visitor
The picture above was taken from the same
location and shows the Mendenhall Glacier as of 2012.
It seems probable that at least the lower portion of
the Mendenhall Glacier will not be visible from the visitor center
in another 20 years. It is important to remember that the
Mendenhall and Taku Glaciers have the same source area – The
We will return to the subject of the low elevation of
the Taku Glacier and the consequences of global warming in the “5)
Why the Taku Glacier is going to start retreating at >= 500 ft.
per year” section.
A second major feature of the Taku Glacier is that it
is a “tidewater glacier”. Tidewater glaciers terminate at sea
level or in terminal moraines that protect them from the ocean.
The Taku Glacier is the only glacier that starts in the Juneau
Icefield and terminates at sea level. It is this “tidewater
glacier” feature that is responsible for the Taku’s advance over
the last century.
2) A model for tidewater
and how this applies to the Taku Glacier
The picture above depicts the major features of a
glacier. The source for the picture can be found at http://slideplayer.com/slide/8509495/
The following equations apply to all glaciers. If a
glacier is going to remain stable, then:
Snowfall on the glacier =
melting + calving
: Ice calving, also known as glacier calving or
iceberg calving is the breaking of ice chunks from the edge of a
If we remove the restriction “If a glacier is going
to remain stable”, then we get a more complete equation that tells
us whether a glacier will grow or not.
Snowfall on the glacier =
melting + calving + glacier growth
or alternately by rearranging terms
Glacier growth = snowfall
on the glacier - melting - calving
(Note that “glacier growth” can be negative)
If snowfall is greater than melting + calving, then
the glacier will grow. If snowfall is less than melting + calving,
then the glacier will shrink.
Calving is an important part of the mass
balance/budget of a tidewater glacier. Thus we must look at the
Tidewater Glacier Cycle which is superimposed on glacial changes
from ordinary climate changes.
Cyan = glacier
Blue = water
Brown = terminal moraine (push moraine)
Gray = bedrock
The diagram above is from
illustrates a tidewater glacier cycle. In the initial part of the
cycle, a tidewater glacier is stable in a “retracted” state. When
a glacier is stable, snowfall = melting + calving, and the
“glacier growth” is zero.
However glaciers carry rocks and debris, and
deposit the rocks & sediment in a terminal moraine. As the
terminal moraine of a tidewater glacier becomes larger, it begins
to restrict warm water access to the terminus of the glacier. This
decreases melting & calving, and eventually cuts off the
calving part of the equation. Even if snowfall decreases slightly,
the glacier begins to grow because the melting & calving parts
of the equation decrease faster than the snowfall component. From
1890 to about 2014 the Taku Glacier progressed from the
“Retracted” to the “Extended” stages as illustrated above. In
terms of distance for the Taku, this advance was about 4.5 miles.
As of 2017, it appears that the Taku Glacier is
at the “306 yr” stage of the tidewater glacier cycle. In terms of
what happens next, it should be noted that the retreat part of the
cycle happens very rapidly. We will cover the “what happens next”
in the “5) Why the Taku Glacier is going to start retreating at
>= 500 ft. per year” section. But first, we will look at “3)
The history of the Taku Glacier” which includes the “Retracted” to
“Extended” part of the tidewater glacier cycle.
3) The history of the Taku
The known history of the Taku Glacier dates back
to the 1700s and is a result of excellent field work done in
the 1940s by Donald Lawrence who was a professor of botany at
the University of Minnesota, Minneapolis. Dr. Lawrence
analyzed vegetation above and below old trimlines and moraines
throughout the Juneau Icefield area. Using this information he
could he could discover the extent of the Taku Glacier (and
other glaciers) and when they were leaving records of their
presence at various locations.
(Click on the above diagram to see a larger version that
includes a description of the features. - recommended)
The diagram above was part of Dr. Lawrence’s
paper that was published by the American Geographical
Society’s Geographical Review.
The dotted lines show where the terminus of the
Taku Glacier was as of various dates, and most important, the
Taku’s maximum extent. In the middle 1700s the Taku Glacier
reached Taku Point – thus blocking the Taku River - which
created a lake upstream from Taku Point.
When the lake overflowed, the river scoured
(removed all previous vegetation) from parts of Taku Point.
New vegetation began to grow after this scouring about
From Dr. Lawrence’s paper:
“At Taku Point (Figs. 6, 9) a first-generation
forest that began to grow about 1755-1757 stands immediately
below the trimline, and a very old forest perched on rotten
logs and surely undisturbed since 1390 or earlier stands
above the trimline.”
Thus the maximum extent of the Taku Glacier had
to occur slightly before this date. The year 1750 is commonly
used for this maximum extent. (Note the “or earlier” could be
as much as 8,000 years)
More recent investigation of the “Forested
Moraines ?” in the lower left quadrant show that the sediments
in that area are layered deposits. Since glacial moraines are
a mixed jumble of sediments, the “Forested Moraines ?” were
deposited via the Taku River and are not a glacial moraine.
Thus the maximum extent of the Taku Glacier circa 1750 was to
just reach Taku Point (and this maximum extent probably did
not last more than a decade or two).
Note: There has been some controversy as to whether the Taku
Glacier made it to Taku Point on the southeast side of Taku
The picture above is a close-up Google Earth view
of some of the rock ledges at Taku Point. There are some
taller trees on higher ground in the upper right corner. The
rock ledges are sparsely covered with smaller vegetation. Even
in a rain forest, vegetation does not grow well without
adequate soil. It is the author's conclusion that something
scraped the soil off the rock ledges within the last few
hundred years. The author sides with Lawrence on this one.
The diagram above is from Fig. 89 of the USGS
publication “Part 3 - Descriptions of Alaska’s 14 Glacierized
Geographic Regions”. https://pubs.usgs.gov/pp/p1386k/pdf/04_1386K_coastmts.pdf
In turn the USGS publication adopted it from the published work of
Post and Motyka (1995). The lines drawn on the Taku and
Hole-in-the-Wall Glaciers show where the respective terminuses
were as of various dates since 1750.
Notes: If you use Google Earth, the 1750 terminal moraine can be
easily seen north of the current terminal lobe of the
Hole-in-the-Wall Glacier. A 1934 extent line for the
Hole-in-the-Wall Glacier could be added using the historic aerial
photo of the Hole-in-the-Wall Glacier (shown subsequently below).
The first European to visit the Taku Glacier was the
explorer Vancouver who sailed up Taku Inlet in Aug. 1794. At that
time the area that is currently occupied by the last couple of
miles of the Taku Glacier was a fjord. Vancouver’s description of
the area as quoted from Roman Motyka’s “Taku Glacier Advance –
Preliminary Analysis” ( http://pubs.dggsalaskagov.us/webpubs/dggs/pdf/text/pdf1989_012.pdf
He reported large numbers of floating icebergs in
Taku lnlet especially at the entrance, through which "passage
was with difficulty effected". At a point about 21 km (13 mi) up
the inlet (the approximate vicinity of Taku Point) he describes
"the shores spread to the east and west, and formed a basin
about a league broad, and 2 leagues across, in a N.W. and S.E.
direction, with a small island lying nearly at its north-east
extremity" (1 league = 3 miles = 4.83 km), and further describes
"immense bodies of ice, that reached perpendicularly to the
surface of the water in the basin". This description fits the
tidal basin that existed in front of the Taku Glacier terminus
when it was first charted in 1890 by the USC&GS (fig. 2) and
would place the terminus well up-fjord but still fronting in
tidewater in 1794 as icebergs were apparently quite common.
There was no further useful information about the
Taku Glacier area until the U. S. Coast and Geodetic Service
created the first map in 1890.
(The picture above is a copy of the USC&GS 1890 map as shown
in Motyka’s paper)
In addition to the Taku Glacier’s retreat since 1750,
there are two items of interest. The first is the 300+ foot depth
of the fjord immediately downstream from the Taku's 1890 terminus.
The second is “Hole-in-the-Wall Lake” near the top edge of the
diagram. The subsequent advance and thickening of the Taku Glacier
would spread ice across this 1.2 mile long lake and over the low
ridge east of it to form the Hole-in-the-Wall Glacier. The west
end of the lake was probably bounded by a lateral moraine from the
When the results of Lawrence, Vancouver, and
the USCGS (and subsequent observations of the Taku) are combined,
we get a picture of what has been happening to the Taku over the
last 300 years.
The solid line in the above chart is from a paper by
Nolan, Motyka, Echelmeyer, and Trabant that was published in the
Journal of Glaciology ( https://www.igsoc.org/journal/41/139/igs_journal_vol41_issue139_pg541-553.pdf
). It shows the known positions of the Taku Glacier’s terminus
starting with 1750, while the dashed line is a best estimate of
where the terminus was in-between Vancouver’s trip and the USCGS’s
map. From the Taku’s maximum extent at Taku Point in 1750, it
retreated some 10 to 11 km (to near or slightly downstream from
the location where the Hole-in-the-Wall Glacier currently branches
off), and then (anomalously compared to most other glaciers) the
Taku advanced until “about” 2014.
The first known photographs of the Taku Glacier date
from 1891. Several 1891 photos are known to exist, but the photo
below is perhaps the best.
The photo above is from the Eastman collection.
The Taku Glacier presents a steep calving face which
is typical of tidewater glaciers terminating in deep water. There
was probably a submerged terminal moraine well below the water’s
surface, but it will be decades before it becomes large enough to
be visible. The mountains in the center and right background are
Goat Ridge. The present location where the Hole-in-the-Wall
Glacier splits off the Taku is just off the right edge of the
At the time of the photo, the fjord was about 300
feet deep at the photographer's location. The same area now is
covered by ice that extends about 1,100 feet above sea level.
Shortly after the above photograph was taken, the
tourist “cruise boat” industry took off. The following two photos
show a couple of the early steamships bringing sightseers to the
“wonders of Alaska”.
south end of Goat Ridge in the distance behind the Brassier Hills.
Currently, the Taku overflows a low ridge in-between these
mountains to form the Hole-in-the-Wall Glacier.
The original source of the above 1907 picture
of the steamship Spokane in front of the Taku Glacier can be seen
The original source for the above 1929 aerial view is:
In the above aerial photo, note the deep
water-filled fjord in front of the glacier. (Work by Motyka gives
a depth of 300 feet.) That deep fjord is still there except it is
currently filled with the Taku Glacier’s ice. In a few short
decades, it’s all going to be water again.
History of the Taku’s
distributary – The Hole-in-the-Wall Glacier
By the 1930s, the thickening of the Taku
Glacier started to push an arm eastward over the old
Hole-in-the-Wall Lake. The photographs below show what happened
The photograph above is courtesy of the Glacier
Photograph Collection at the National Snow & Ice Data Center.
The picture above shows the Hole-in-the-Wall Glacier
as of 1934 before the Taku Glacier thickened enough to overflow
the low ridge between the Brassier Hills (lower left) and Goat
Ridge (upper right). In subsequent years, the Taku Glacier (upper
left) would overflow the low ridge (right-center) onto the low
flats (lower right) – thus forming the Hole-in-the-Wall Glacier.
There is still a very small portion of the former
Hole-in-the-Wall Lake remaining between the glacier and the crest
of the low ridge.
The lack of trees on the low ridge indicates the Taku
had overflowed the area sometime in the previous 200 years, and
had scraped off all the soil that trees would need to grow.
The picture above is a Google Earth
approximation of what the same Hole-in-the-Wall Glacier area
looked like in July 2010. The large crevasses are formed where the
glacier overrides the old low ridge. Note the trimline that is
beginning to form on the left side of the glacier.
The following 3 photographs were included as part of
Dr. Donald Lawrence's paper that was published by the American
The photo above was taken in 1934 and shows the
incipient Hole-in-the-Wall Glacier just before it pushed over the
low ridge. The Taku Glacier flows from right to left in the
The 1941 photograph above shows the Hole-in-the-Wall
Glacier just as it is beginning to overflow the low ridge.
Presumably the dog in the foreground is one of the famous sled
dogs from the Taku Glacier Lodge, and is sitting in the bow of a
small boat. The photographer's location is on the west side of the
Taku River, nearly 2 miles WSW to SW of the Taku Glacier Lodge,
and looks west toward the glacier.
The photographer's location is probably near the
point of land that is just below and to the right of the cataract
in the preceding picture. This would be inside of the southernmost
current lobe of the terminus of the glacier.
By 1949 the glacier had thickened enough to
completely overflow the low ridge. the
Hole-in-the-Wall Glacier would continue to expand for another 55
to 60 years.
The photograph above is courtesy of the Glacier
Photograph Collection at the National
Snow & Ice Data Center. http://nsidc.org/data/glacier_photo/search/
The photograph is an aerial view of the Norris
Glacier (left) and the Taku Glacier (right) as of 1948. Up until
the 1940s, the terminal (push) moraine in front of the Taku had
not grown large enough to appear above sea level; but as of 1948 a
muddy silt flat can be seen in front of the center of the Taku
Glacier. There is a small area of calving remaining on the right
side of the Taku, and this may be the basis of other sources that
state that calving continued to 1953. ( For example: https://www.geographie.uni-freiburg.de/publikationen/abstracts/fgh50-en
By 1948 (at least one source uses a 1953 date -
see above) the terminal “push” moraine had grown to the point
where there was no ocean water contact with the Taku Glacier. The
“snowfall on the glacier = melting + calving” portion of the
equation was still out of balance as “calving” had disappeared
from the equation. The Taku would continue to grow for decades to
The picture above shows the position of the Terminus
of the Taku Glacier from 1948 to 2014. The original picture can be
As of 1948 the Taku Glacier was still advancing
rapidly. The advance slowed after 1973, but still continued up to
2014. As of 2014 it looked like the Taku Glacier had reached the
“Extended” stage of the “tidewater glacier cycle” diagram.
The picture above is a PrintScreen image from the
Juneau Icefield Research Program’s blog. http://juneauicefield.com/blog/2017/8/31/the-mass-balance-student-research-project
The picture shows a historical record of the mass
balance (total ice volume) of the Taku Glacier as well as the
Lemon Creek Glacier (another glacier at the southern end of the
Juneau Icefield) as measured by researchers for the Juneau
Icefield Research Project.
The mass balance (total ice volume) of the Taku
increased from the the first measurements by the JIRP in the 1940s
until 1988. This was the period when the Taku’s growing terminal
moraine protected it from the melting and calving that had been
taking place earlier due to the glacier’s contact with “warm”
Additionally, the moraine was a partial barrier to
the glacier’s forward advance, and thus ice piled up and thickened
behind the moraine. The backup and thickening extended for miles
upstream, and this thickening caused the Taku to overflow a low
ridge to form the Hole-in-the-Wall Glacier.
After 1988, global warming started to catch up with
the Taku. The mass balance (total ice volume) began to shrink. The
pressure from the previously accumulated thickness of the ice
continued to push the terminus forward even while the middle
portion of the glacier began to thin. The process is similar to
what happens when you pour syrup on a stack of pancakes. Even
after you stop pouring syrup, what you have already poured
continues to spread out on your plate while the portion on top of
your pancakes thins.
From 1988 on, the total volume of the Taku Glacier
began to decrease even though the terminus continued to advance a
little more. The thickness in the middle part of glacier started
to decrease from the combined forces of “spreading out” plus
The rate that the Taku’s ice can spread out decreases
as the thickness in the middle part of the glacier decreases. Thus
the ice supply to try to push the terminus forward will tend to
Unlike syrup, ice is subject to melting and
eventually disappears. Unfortunately for the Taku, the rate of
melting continues to increase since the surface area of the
glacier subject to melting has increased as well as global warming
has increased the melt rate per unit area. Sooner or later,
the increase in melting from global warming will overwhelm all
parts of the glacier.
Source for the above diagram is the 1995 paper by Nolan, Motkya,
Echelmeyer, and Trabant.
Please see the source article for information about the sampling
The diagram above shows a longitudinal (lengthwise)
cross section of the Taku Glacier starting at Taku Point on the
left end and extending some 60 km. (37 miles) upstream to Matthes
Divide on the right end. The Hole-in-the-Wall Glacier splits off
just to the right of the Brassiere Hills label. The top line shows
the 1990 surface elevation of the glacier (in meters) above sea
level. The bottom line shows the elevation (in meters) of the base
of the glacier.
There are several items of interest. First, the base
of the glacier is below sea level up to the 40 km. (25 miles)
mark. When (not “if”) the Taku Glacier melts, it’s lower portion
will be replaced by a 20-mile long lake. (It is assumed that the
Taku’s terminal moraine remains intact and/or it is augmented by
silt transported in by the Taku River. Thus it will be a lake
instead of a fjord connected to the ocean.)
A similar process of a melting glacier forming a long
lake is already underway at New Zealand’s Tasman Glacier. (The
Tasman Glacier has been retreating at 500 feet per year for the
last 30 years. A chart showing the retreat of the Tasman Glacier
is shown at the end of the
“5) Why the Taku Glacier is going to start retreating at
>= 500 ft. per year”
section at the bottom of this webpage)
Also, the glacier has scoured out another 300 feet of
sediments in addition to the 300-foot deep fjord that existed in
front of the 1890 terminus. The 300-foot deep area downstream from
the 1890 terminus is now ice down to 600 feet below sea level.
It’s going to be a very deep lake.
The separation of the two lines in the above diagram
shows how thick the Taku Glacier is. At a little upstream from the
“Goat” measuring point, the Taku Glacier was some 1477 meters
(4,800+ feet) thick as of 1990 making it the thickest known
glacier outside the polar icecaps. As the lower end of the Taku
starts melting, this thick portion will thin rapidly as ice will
ooze rapidly downstream to try to fill in the void. (Eventually
this thick portion and everything downstream will end up floating
on the growing lake.)
The equilibrium line marks the 1990 position that
separated the “accumulation zone” (The right side where more snow
falls than melts) from the ablation zone (The left side where more
ice melts than snow falls). Since 1990 this equilibrium line has
moved higher (moved to the right) due to global warming, and will
continue to move higher in the future.
By 2015 the advance of the Taku Glacier had come to a stop.
“Taku Glacier's advance stagnates”
Another analytical method for measuring the "health"
of a glacier is to measure the accumulation area of a glacier (The
portion of a glacier where snowfall is greater than melting) vs.
its total area. This is commonly referred to as the Accumulation
Area Ratio AAR).
The graph above was published by M.S. Pelto in 2008
and can be seen at http://www.nichols.edu/departments/glacier/taku.html
Pelto had previously concluded that glaciers that had a AAR that
was significantly less than 67% were shrinking while those that
had an AAR significantly greater than 67% were growing. Glaciers
that had an average AAR near 67% would be in approximate
There are several items of interest. First, many
sources quote an AAR for the Taku Glacier in excess of 80%. Note
that this is a very old number and is thus not relevant to current
2nd: The AAR for the Taku Glacier has been declining
for decades. As of the 2008 publishing date (and the research data
for this date was already several years old), the AAR for the Taku
had already dropped to near the critical 67% ratio.
3rd and most important. Note the statement "Due
to the large area between 1200 and 1600 meters, minor increases
in temperature may result in dramatic changes in Taku Glacier
If the ELA (Equilibrium Line Altitude - The
line that separates the accumulation zone from the ablation zone)
rises above 4,000 ft. (1312 meters), then the AAR will drop below
the 67% ratio; and the Taku Glacier will be shrinking.
The table above is from "Quantifying Changes in
Glacier Thickness and Area Using Remote Sensing and GIS: Taku
Glacier System, AK ( https://spatial.usc.edu/wp-content/uploads/2017/11/Hughes-Allen_Lara.pdf
), and updates the AAR for the Taku Glacier up thru 2015. As of
2015, the average AAR for the Taku Glacier had dropped to the
critical 67% level. (The last column shows the ratio between the
AAR and the critical 0.67 level.)
In June 2017 the author took a sightseeing flight
(Wings Airways) over the Taku Glacier, and its distributary, the
Hole-in-the-Wall Glacier. The author took videos of the Taku and
Hole-in-the-Wall Glaciers and posted the result to YouTube.
The relevant portion of the video begins at 13:07
into the video. As of 2017 it looks like the Taku Glacier has
reached the “306 yr” stage of the tidewater glacier cycle diagram.
It appears that the retreat of the Taku Glacier has begun.
4) What is happening now to
the Taku Glacier
The following pictures are from the author’s
sightseeing flight over the Taku and Hole-in-the-Wall Glaciers in
June 2017. Please see the author’s video at https://www.youtube.com/watch?v=O5v_Bf3cbHI&feature=youtu.be
– especially the part beginning at 13:07 for more views.
The Hole-in-the-Wall Glacier is part of the Taku
Glacier’s distributary system. (Please see the pictures in the “1)
The Taku Glacier and its source – the Juneau Icefield” section )
The Hole-in-the-Wall Glacier formed in the 1940s when the Taku
thickened enough to flow over a low ridge. Whatever the Taku
Glacier does (advance or retreat), the Hole-in-the-Wall Glacier
will do the same.
The picture above is a PrintScreen image from the
author’s video, and shows the June 2017 position of the terminus
of the Hole-in-the Wall Glacier. The terminus is retreating from
the trees. We can compare the above picture with 2010 and 2006
views as seen via Google Earth.
The picture above is a Google Earth view of the same
area but as of April 2010. The trees are the same as in the view
from the 2017 video. (The Google Earth view has a lot of extra
mud, but otherwise the view is approximately the same.)
The picture above is a Google Earth view of the same
area but as of July 2010. (The bright area is a carryover from
April 2010 as it wasn't included in the July 2010 image.)
In 2010 the glacier was threatening to obliterate the
trees. But in 2017, the trees are still standing and the terminus
is further away. (In the July 2010 Google Earth view, the glacier
has retreated a little bit from the trees, but not as far as shown
in the June 2017 view.)
The picture above is a Google Earth view of the
terminus of the Hole-in-the-Wall Glacier as of May 2006. The
terminus of the glacier is nearly (but not quite) the same
distance from the trees as the 2017 picture; but more important,
the most advanced terminal moraine was in place before 2006. We
can thus deduce the following chronology.
1) The glacier advanced sometime before 2006, and
almost reached the trees.
2) The glacier retreated by the time the 2006 photograph was
3) The glacier advanced up to 2010, but didn't quite reach the
4) The glacier has retreated from 2010 to 2017.
Landsat photographs (which have a much lower
resolution) suggest that the maximum extent of the
Hole-in-the-Wall Glacier occurred about 2003.
Thus the glacier's advance has been stalled for at
least 11 years - and more likely, since about 2003. Meanwhile,
thinning is taking place (see below) on the Taku's surface The
thinning will make it difficult for the glacier to stage any more
advances, while at the same time global warming marches onward.
The pre-2006 terminal moraine will probably not be challenged
Logically, the Hole-in-the-Wall's terminus should
retreat before the Taku's terminus retreats since the
Hole-in-the-Wall Glacier suffers a greater percentage decline in
its ice supply for any given thinning of the Taku (See below).
(Remember, the ice supply for the Hole-in-the Wall still has to
climb over the old buried ridge.)
The picture above is a PrintScreen frame from the
author’s video which can be seen at https://www.youtube.com/watch?v=O5v_Bf3cbHI&feature=youtu.be
The sightseeing flight is over the Taku Glacier. Taku Inlet can be
seen in the upper right. The mountain in the left foreground is
the Brassiere Hills ridge between the Hole-in-the-Wall Glacier and
the Taku Glacier.
When a glacier is growing, it obliterates any
vegetation in its path. When a growing glacier thickens, it
obliterates any vegetation in its path along the side walls of its
On the left side of the picture there is a sliver of
rock between the glacier and the trees. When the Taku Glacier was
growing and thickening, it “trimmed” all vegetation that was in
its path. The line marked by trees on top and rock underneath is a
“trimline” It is a record of how thick the glacier was when it was
at its thickest.
The bare rock is a zone where the glacier has removed
everything except the solid rock. In order to see the bare rock
area, the Taku Glacier had to thin. The area in the photograph is
more than 2 miles upstream from the glacier’s terminus. The Taku
Glacier is melting and thinning 2 miles upstream from its
terminus. This is telling us what will happen downstream at the
terminus a few years in the future. The Taku Glacier has started
The trimline is perhaps the best available clue for
letting us know whether the Taku is in an advancing or retreating
mode. The picture above is digitally enhanced portion of a frame
from the original video.
The picture above is a Google Earth view that
contains approximately the same field of view but as of July 2010.
(The flat rocks just above the trimline near the center of both
pictures can be used as a reference guide.) The glacier had
apparently reached its maximum thickness slightly before July
2010, but the thinning as of 2010 was no where near as much as
that shown in the 2017 view.
This thinning of the glacier is extremely
important. The thinning is more than a few inches. It’s not easy
to get an accurate measurement of the amount of thinning as viewed
from an airplane, but the trees in the background should give some
idea of the scale.
The picture above is a Google Earth view of the
terminus of the Taku Glacier as of July 2010.
The picture above shows approximately the same area
of the terminus of the Taku Glacier, but as of June 2017.
There are two items of interest.
1) The terminus of the Taku Glacier has retreated from 2010
to 2017. The maximum extent was probably greatest about 2014 (+/-)
The July 2010 Google Earth view doesn’t show any retreat yet. By
June 2017 there is a noticeable gap between the glacier and the
2) In the 2017 picture there is a small innocuous-looking
melt-water pond next to the glacier in the foreground of the
picture. This small pond (and what will follow) is a source of
water that can tunnel its way underneath and start melting the
glacier from the bottom up. Water is its densest at about 39 deg.
F. Water at 39 deg. F. will sink below water at any other
temperature; and of course, water at any temperature will sink
below ice if it has any possible way of doing so. 39 deg. F. water
is not warm enough to encourage swimmers, but it is warm enough to
Glaciers are full of cracks and crevices, and
water will find any available opening to sink downward as water is
denser than ice. In the tidewater glacier cycle diagram, the “306
yr” diagram shows a “Void opening”. The innocuous-looking
meltwater pond in the 2017 view is the start of a “Void opening”,
and marks the start of the collapse of the Taku Glacier. And the
innocuous-looking meltwater pond (or something similar to follow)
may very well be the start of what will become a 20-mile (+/-)
5) Why the Taku Glacier is
going to start
retreating at >= 500 ft. per year
In part 2), we looked at the tidewater glacier cycle.
Even if nothing else changed, a tidewater glacier retreats rapidly
once retreat sets in. This is because the lake (or ocean) in front
of the glacier melts both the front end and underneath part of the
In turn, if we look at the basic equation for glacial
balance (Snowfall = melting + calving), once a tidewater glacier
starts melting back, it will start calving rapidly. Thus the
ablation side of the equation becomes larger, and the glacier
Global warming will also hit the “snowfall” side of
the equation. We saw earlier that large portions of the Taku
Glacier are at relatively low elevations. As global warming
continues to progress, the precipitation over large portions of
the glacier will change from predominately snow to predominately
We can apply all of these changes to the
complete equation for a glacier's budget.
The complete equation is:
Glacier growth = snowfall
on the glacier - melting - calving
The changes that will be taking place are:
Snowfall on the glacier - Decreasing as global warming changes
snowfall to rainfall
Melting - Increasing as air temperatures warm and a lake melts the
Calving - Increasing as the front end of the glacier calves into
Any one of the above will force "glacier growth" to
become negative. The combination of all three will force "glacier
growth" to become strongly negative.
In regard to the estimate that the Taku Glacier will
retreat at 500 (or more) feet per year, we only have to look at
what has happened in the past.
The diagram above is the same diagram that we
looked at earlier when were looking at where the terminus of the
Taku Glacier has been over the last 300 years. The lowest part of
the graph tells us how fast the Taku was advancing or retreating
during this 300 year interval. If we look at the portion from 1750
to 1794 (From Lawrence's trimline analysis to Vancouver's visit),
the Taku retreated at some 170 meters (550+ feet) per year. The
climate has warmed significantly since the 1700s, and will
continue to warm in the future. The 500 feet per year retreat rate
may be overly conservative.
The first few years of retreat for the Taku will be
relatively slow – less than 100 feet of retreat per year. Once a
lake starts to appear behind the terminal moraine, the retreat
rate will pick up. In 20 to at most 30 years, this retreat will
accelerate to 500 or more feet per year as serious calving begins.
New Zealand's Tasman Glacier
is a model for what is expected to happen to the Taku
The picture above is a 2013 Google Earth view
of New Zealand's Tasman Glacier and Tasman Lake. The debris
covered lower portion of the glacier extends from the far side of
the lake back toward the distant mountains before it bends to the
right and disappears out of sight. The high mountain to the left
is Mt. Cook. The yellow "ruler" that runs across the lake is over
3 miles long and measures the retreat of the terminus of the
glacier since it started backing off from its terminal moraine in
The chart above is from
and shows the retreat of several of New Zealand's glaciers -
including the Tasman. (Original source was in Nature
) The terminal position of the Tasman Glacier (dark red line) is a
model for what is expected to happen to the Taku Glacier.
From the late 1800s to the early 1970s, the Tasman
Glacier was steadily pinned to its terminal moraine (near side of
the lake). As the Tasman began to slowly retreat in the late
1970s, a growing, 800 foot deep “proglacial” lake began to form
between the glacier's terminus and the old terminal moraine. From
the mid 1980s on, the Tasman Glacier has been calving icebergs
into the lake. (For example, the distant iceberg to the left of
the top of the yellow line is about 1,200 feet long.)
100 years ago there was a deep fjord suitable for
ocean-going ships in front of the Taku. This was subsequently
filled in with ice. A few decades from now the fjord will become a
deep lake with a rapidly calving (and retreating) glacier at the
200 years from now, if you travel to visit the Taku
Glacier, you will instead find a large lake (about 20 miles long).
There will still be much smaller glaciers in the higher mountains,
but most of what is now the Juneau Icefield will have become lakes
and newborn forests.
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