USGS Public Lecture: Warm Ice—Dynamics of Rapidly Changing Glaciers

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Detailed Description

  • Glacier Numerology – The how big, how long, how thick, how much, how often, of glacier science.
  • Glacier Photography – While a picture may be worth a thousand words, a collection of images may tell a complete forensic story.
  • Glacier Geophysics – How new technologies are being introduced to reexamine and refine decades old glacier analyses.


Date Taken:

Length: 01:25:41

Location Taken: Menlo Park, CA, US


… [voice in background]
and then I wanted to do my Ph.D.

on something that was
glacially related, and I got –

fortunate that the Navy had a
program that I was able to get into.

And I was out on a Navy research
vessel [inaudible] cores in the

north Atlantic Ocean that were
these sequences of marine fossils

interbedded with iceberg-
transported sediments.

[background conversations]

- So again, thank you all for
coming to our July public lecture.

Welcome to the
U.S. Geological Survey.

I am William Seelig.

I am with Science Information
Services here in Menlo Park.

And that’s probably a little better.
There we go.

Quick reminder
before we get started.

Our August lecture next month
will be held on the 31st.

The title is – the subject is Mars Rover – 
Curiosity’s Exploration of Gale Crater.

You can pick up a flier
on the back table over there.

Tonight’s lecture is titled Warm Ice –
the Dynamics of Rapidly Changing

Glaciers presented by
USGS’s Bruce Molnia.

So a little bit about Bruce.
Bruce is – he’s a Ph.D.

And he has served as the USGS
senior adviser for the National Civil

Applications unit and is also an
award-winning research geologist.

He’s conducted glacial, marine,
and coastal research for over 50 years.

His current activities focus on
innovative uses of remote sensing,

the responsive glaciers in
Alaska’s changing climate,

presenting understandable science to the
public, policymakers, and the media.

Mr. Molnia, who has been awarded
the DOI Meritorious Service Award,

the USGS Lifetime
Communications Achievement Award,

and the Geological Society of
America’s Career Achievement and

Public Service Awards, as well as three
USGS external communication awards.

He has authored
more than 350 articles,

abstracts, books, and maps,
mostly focused on the Alaskan region.

Dr. Molnia has worked for the USGS in
Menlo Park from the years 1974 to 1983.

So, again, please give
a warm welcome to Bruce.

And please hold all questions
until after the lecture. Thank you.

[ Applause ]

Good evening.
How are you?

So as you’ve heard,
my name is Bruce Molnia.

I am a research geologist and
have spent more than 40 years

working for the U.S. Geological Survey.
And my focus has been on trying to

understand the dynamics
of rapidly changing glaciers.

And what I’m going to do is make a
presentation that has three components.

First part I call glacier numerology.
It’s the how big, how long, how thick,

how much, how often –
about basic glacier information.

Then we’ll talk about glacier
photography, focused on Alaska.

And we’ll look and
see what imagery can tell us

about the dynamics
of Alaskan glaciers.

And then finally, I’m going to
describe a research project

that I’ve been involved with
for quite a number of years.

And it’s one that is focused
on the use of geophysics.

And what’s remarkable is, about every
decade, a new technology evolves.

And each new technology allows us
to get new insights into addressing

a problem that we started to try
to understand in the mid-1970s.

A lot of what I’m going to say
is already in print in a

USGS professional paper that
came out about a decade ago –

the Alaska chapter of the Satellite Image
Atlas of the Glaciers of the World.

And a lot of this numerology, especially
related to sea level change, is on

a website that I have. And you can see
the URL of the website at the bottom.

On this website,
the professional paper is also available,

and you can download it
or just look at it online.

So some
basic definitions.

Let’s begin with a glacier.
“Glacier” is, by definition,

larger than a square kilometer,
or about 4/10ths of a mile.

It’s a perennial accumulation of ice and
snow, rock, sediment, liquid water.

It originates on land and
moves downslope under the

influence of its
own weight and gravity.

Glaciers form from the metamorphism –
the recrystallization –

of snow into hexagonal
glacier crystals – ice crystals.

And glacier ice has a density of 0.91.
Liquid water has a density of 1.0.

That’s why icebergs float with
90% of the iceberg submerged.

An ice sheet is a large mass
of glacier ice, typically with areas

greater than 50,000 square kilometers –
20,000 square miles.

And today, ice sheets cover most of
Greenland, and there are two in

Antarctica – the large West Antarctic
and East Antarctic Ice Sheets.

During the last Ice Age –
the Pleistocene – ice sheets also

covered large parts of
North America and Scandinavia.

An ice shelf is a permanent, floating
sheet of ice that connects to a land mass.

They form where glaciers actually leave
the terrestrial environment and

move into the ocean. And because
of the density of the ice, it floats.

Around Antarctica, where there are
more than 40 of these ice shelves,

the topography, or the bathymetry,
of the continental margin is

extremely different from
what we’re used to here

on the West Coast or the
East Coast of the United States.

There, it is extremely
deep at the shoreline.

You go offshore,
and you’re already in

400 or 500 meters of
water in many places.

So these large masses
of glacier ice leave the continent

and float out into
the Antarctic oceans.

Antarctica has, as I said,
more than 40 of these.

And one, the Larsen C Ice Shelf,
has gotten quite a bit of attention

in the last few weeks, as a part of it
that represented about 100 – I’m sorry –

a trillion metric tons of ice broke off
and is now known as iceberg B68.

So let’s get into
the glacier numerology.

I titled my talk Warm Ice,
and you might want to know

the difference between
warm ice and cold ice.

Warm ice is the ice that we find
in most Alaskan temperate –

European temperate glaciers.
And the temperature of the ice

is within a very small fraction of
a degree of the melting point.

So in terms of Fahrenheit,
a typical glacier will have liquid water

in contact with the ice crystals,
and the temperature of the ice at the

surface may be only about a tenth of
a degree below the freezing point.

At the South Pole,
if you were to measure

the temperature of
the ice at the surface,

it’s minus 50 degrees Fahrenheit –
about minus 45 degrees Celsius.

So there’s a significant difference
between the behavior of warm and

cold ice. Warm ice flows very plastically,
deforms without fracturing.

Cold ice is very
brittle and shears.

So we’re talking today,
for the most part,

about the dynamics of Alaskan
glaciers, which are warm ice.

But to go back to the
South Pole environment,

there you’ve got 2,800 meters of ice.
You’ve got 9,000-plus feet of ice.

And the temperature at the surface,
about minus 50 Fahrenheit.

Temperature at the bottom,
about minus – about plus 15 degrees.

It’s only about 20 degrees
below the freezing point.

But in the middle of that
9,000-foot thickness of ice,

the ice temperatures may be
minus 40 degrees Fahrenheit.

So there’s a
very, very significant difference

between warm ice
and cold ice.

And warm ice, just because of the fact
that it is so close to the melting point,

is extremely susceptible to
rapid melting when you get

temperature increases as we’ve been
experiencing in the last century.

The number of glaciers on Earth –
about 200,000.

These are glaciers
larger than 1 square kilometer.

If you count all of the
sub-square-kilometer glacierets,

the number goes up
to about 450,000.

This number does not
include the big ice sheets.

When did glaciers first appear?
Well, the evidence in the

geological record goes back
2,900,000,000 years ago.

So glaciers are not
a modern phenomenon.

They’ve been around for
at least half the age of the Earth.

And if you look at the geological record,
you can find evidence of more than

that are preserved in the rock record.

If there were only

and they represented all of the water,
what we would discover is that

972%– or, 972 of those drops –
97.2% – are in oceans and inland seas.

21 would be in glaciers. Six would be
in groundwater and soil moisture.

And less than one in the atmosphere.
Less than one in all the lakes and rivers

on Earth. And less than one in all the
living plants and animals on Earth.

So although probably very
few of you are aware of it,

glaciers are the single-largest
repository of freshwater on Earth.

So 97.2% saltwater, 2.8% freshwater.
2.1% of that 2.8% glacier ice.

If there were 1,000 ice crystals,
and that represented all of the

glacier ice on Earth, we’d discover
that 914 of them are in Antarctica.

79 in Greenland.
Approximately four in North America,

with more than three of them
in the Canadian arctic.

Approximately two in Asia.
And less than one in South America,

Europe, Africa, New Zealand,
and the island of Irian Jaya,

which is New Guinea
in Indonesia.

So 99.3% of the glacier ice on Earth is
polar – in Greenland and Antarctica –

and 7/10ths of 1% is
temperate glacier ice.

How much ice is there on planet Earth?
About 16,434,000 square kilometers,

of which 14 million are in Antarctica.

And all of the others on Earth,
only about a little bit more –

approximately 3/4 of a
million square kilometers.

So Antarctica,
without question,

the greatest concentration
of glacier ice on Earth.

Last time that Antarctica’s
ice cover melted completely away,

20 million years ago.

Last time Greenland was ice-free,
about 110,000 years ago.

about 20 feet higher than it is today.

And at that point in time, the Fall Line,
which is a feature on the East Coast,

at the inner edge of the
coastal plain, was formed.

And the Fall Line is a major
erosional scarp that marks the

extent of the Atlantic
Ocean 110,000 years ago.

Glaciers exist
on six continents.

The only continent without
glacier ice is Australia.

Although, in the geological
record of Australia, there are

several geological units that
contain glacier-transported rocks

going back, in this case,
about 350 million years ago.

In Alaska, there are 14 different
regions that support glacier ice.

And what most people don’t realize,
almost all of the glacier ice in Alaska is

along the southern coast of Alaska – the
southern coast and in the Alaska Range.

Alaska Range
is this area here.

Once you get north of the Alaska range,
you’re moving into a sub-polar desert.

And so the existence of glaciers
in Alaska is concentrated around

the Pacific Ocean because it’s the
Pacific Ocean moisture source

and the presence of
very high mountains

that contribute to the formation
of the glaciers of southern Alaska.

There’s a period of time
from about 1250 A.D.

to 1900 A.D. called
the Little Ice Age.

And during the Little Ice Age,
glaciers on the six continents

that currently support them
expanded dramatically.

Winter temperatures were
as much as 4 degrees Fahrenheit –

2.8 degrees C –
lower than there were today.

And the coldest part of the
Little Ice Age was the second half

of the 17th century and the
early part of the 18th century.

During that period of time,
most of the larger glaciers in Alaska

expanded to what we call their
Little Ice Age maximum positions.

And they’ve been
retreating in many, many places,

in some cases,
for the last 250 years.

Total amount of glacier ice in Alaska
today is about 86,000 square kilometers.

It’s about
33,000 square miles.

There are two – excuse me –
there are 26,000 glaciers

in Alaska larger than
a square kilometer.

Of that, about 2,000
are large valley glaciers.

And of those 2,000 large valley glaciers,
only about 700 have names.

So two-thirds of
the glaciers in Alaska –

the large glaciers in Alaska –
are unnamed.

The biggest glaciers in Alaska – the
Bering and the Malaspina – are complex

glacier systems with many tributaries
and complex piedmont lobe termini.

And those two glaciers each
are about 5,000 square kilometers.

Those two glacier systems reach
about 5,000 square kilometers in area.

Today, of all the
valley glaciers in Alaska,

more than 99% are currently
retreating, thinning, or stagnating.

And most notably, you see
this at the lower elevations.

There are many places where
lower-elevation glaciers have

completely disappeared during
the 20th and 21st centuries.

However, just to make things
more complicated, there are

a handful of Alaskan glaciers
that are currently advancing.

And we can talk about why
that’s happening a little bit later.

Temperatures in Alaska
are very interesting.

This is a map showing the
location of the 19 first-order

U.S. National Weather
Service weather stations.

And if you look at the average 
temperatures, you can see that,

between 1949, when the weather
stations were established, and 2016,

the mean annual – the mean
seasonal annual temperatures

in Alaska have increased by
more than 3-1/2 degrees Fahrenheit.

But also, if you look at the seasons,
you see that the single-greatest increase

in temperature has been in winter.
So winters in Alaska are warming.

Last year was an abnormally
warm year in Alaska.

And the average temperature last year
was more than 6 degrees Fahrenheit

warmer than the moving average of
temperatures since the 1940s.

If you look at these three diagrams on
the right-hand side, you can see that

pre-1970, Alaskan temperatures were
significantly colder than the long-term

norm. And then, in the mid-’70s,
temperatures dramatically increased.

And this is due to a shift
in atmospheric circulation

of something called the
Pacific Decadal Oscillation.

When it moves northerly, it brings
warmer, wetter ocean air over Alaska,

and temperatures warm.
When it moves southerly,

it allows much colder arctic air to
cover most of the surface of Alaska.

And so, even though it’s called a
“decadal” oscillation, it actually

seems to have a duration of many
decades – 40 or 50 years, at least.

But if you also look at
the diagram on the upper right,

you can see that the last few years
have been significantly warmer

than any of the other years in the
post-World War II time period.

So what does that mean for glaciers?
And this is a good example.

This glacier, located in the
Chugach Mountains, is rapidly melting,

to the point where these linear stripes
of sediment, which are called moraines,

are actually elevated above the
surface of the rapidly thinning ice.

But there are a number of
other telltale signs in this picture

that allow someone with the
knowledge of glacial geology

to determine what this
glacier has been doing.

The height of the vegetation on the
side here shows that the ice probably

was as thick as where the cursor is
in the not-too-distant past.

And all of this sediment
stranded on the other valley wall here,

this is the lateral moraine
that was the sediment trapped

between the edge of the
ice and the bedrock wall here.

So this is a cirque glacier.
You can see several of its

source cirques up here.
And the ice is rapidly melting away.

And so where is that water going?
It’s going into the oceans.

So global sea level
is rising for two reasons.

One, we’re adding
more molecules of water.

And two, the temperature of those
molecules is increasing, and water

molecules expand as they get warmer.
So that’s called steric sea level change.

So the addition of more
molecules and the enlarging of

the existing molecules
is causing sea level to rise.

How much did it rise in the
last century – in the 20th century?

And these are based on tide gauges –
anywhere from 12 to 22 centimeters,

depending on where
you were measuring.

So that’s between
5 and about 9 inches.

However, not all coastlines are
experiencing sea level rise.

There are many places on Earth,
especially along the West Coast,

where tectonics is actually
elevating the land surface

more rapidly than
sea level is rising.

So if you go to Juneau, sea level
is falling about 2 inches a year.

The Intergovernmental Panel
on Climate Change estimates that,

by the year 2100,
the global average sea level

will rise anywhere from 18 to 59 
centimeters – between 7 and 23 inches.

And this is a diagram
from the IPCC report.

It shows that, from the

there wasn’t any
significant change in sea level.

The light red is the
tidal gauge record.

The green is the satellite
record of sea level change.

And the blue is their prediction of what
sea level might do over the next century.

About 20,000 years ago,
global sea level was about

than 400 feet lower than it is today.

So if you were on the East Coast,
and you were standing at the

current shoreline, everything that
you could see off to the east

would be exposed land surface.
The edge of the ocean was

60 to 80 miles further to the east
back 20,000 years ago than it is today.

And then, about 8% of the Earth’s
surface was covered by glaciers.

25 of the Earth’s land –
25% of the Earth’s land area

and about a third of Alaska.
[coughs] Excuse me.

Today, only about 3% of the Earth’s
surface is covered by glacier ice.

That’s 10% of
the Earth’s land area.

And only about 5% of
Alaska is covered by glaciers.

Between 18,000 years ago,
when sea level began to rise,

and about 6,000 years ago,
when it stabilized at a level

close to what it is today,
the oceans rose more than 125 meters.

And so, when you do the math,
that’s about a meter per hundred years.

Which is comparable
to the prognostication

of the IPCC as to what we might
encounter in the next century.

And then last piece of information
here in terms of glacier numerology is,

as I mentioned before,
the Larsen C Ice Shelf

had a 5,800-kilometer piece
break off between July 10th and 12th

and represented 12% of the
total area of the Larsen C Ice Shelf.

And what we’ve been
seeing over the last 50 years

are what is referred to as
a collapse of ice shelves

around Antarctica with
significant amounts of

calving taking place and large icebergs,
some of which are hundreds of meters –

I’m sorry – hundreds of
kilometers in size, breaking off.

And a lot of this is due to the fact
that the temperature of the

Antarctic Ocean is warming.
And this warmer ocean water is able to

penetrate from the bed of the glacier –
the floating glacier ice, get into cracks

and cause the rapid deterioration
and breakup of the ice shelves.

So let’s talk about
glacier photography.

The first known photograph of
an Alaskan glacier was in 1883.

By 1920, mostly through the efforts of
USGS geologists who were surveying

the mineral resources of Alaska, more
than 400 glaciers were photographed.

By 1929, the first aerial survey of
glaciers took place in southeastern

Alaska, and all the glaciers were
photographed from the air.

By 1960, all of the glaciers
in Alaska were photographed

from the air, mostly by
the Navy and the Air Force.

Also in the 1960s, DoD space-based
satellites began imaging Alaskan glaciers.

And in some of the imagery that’s been
declassified and made publicly available,

there are amazing photographs
of glaciers in the 1960s and ‘70s

taken by the early Corona
and Keyhole satellites.

Beginning in 1972, the Landsat
satellite began to systematically

observe glaciers of Alaska.
And now, some of the glaciers

in Alaska have been imaged
more than 1,000 times.

And in 1976, the first space-based radar
imagery of an Alaskan glacier was made.

So this is the first known
photograph of an Alaskan glacier.

This is the, quote, Muir Glacier
located in Glacier Bay.

was made in 1883.

John Muir discovered – quote, unquote,
discovered – Glacier Bay in 1879.

And within four years,
tourism was extremely prevalent.

There were cruise ships coming up
from both Bellingham, Washington,

and Tacoma, bringing tourists
with cameras to Glacier Bay.

And there are numerous photographs –
pre-1900 photographs of Alaska

taken by these tourists who
came up to explore the Muir Glacier.

Now, even though John Muir, quote,
discovered Glacier Bay in 1879,

the local inhabitants had been
living there for about 4,000 years.


So let me point out
this feature that you see here.

This bedrock mass shows up
in many of the early photographs.

And it’s an important feature because
it allows us to locate the terminus

of the glacier in the early 1880s and
look at how it’s changed over time.

So this is an 1899 photograph
by a USGS geologist

named Grove Karl Gilbert.
And if you just watch what happens,

you can see how the landscape has
changed over a 103-year time period.

And so we went
from the terminus of Muir Glacier

pretty much filling
the entire foreground …

… to glaciers being long gone,
and the closest glacier ice

is about 30 miles away in the
very right-hand side of the image.

The other thing that’s
important to note –

even though this is a
black-and-white image,

if it had been in color, it would still
pretty much be black rock and white ice.

And so we have this progression from
black and white to blue and green.

And so vegetation is
established very, very rapidly.

And you’ll see, in some cases,
it’s so rapid that it’s mind-boggling.

Most of the literature suggests
that ecological succession

takes several hundred years to go
from bare bedrock to a forest.

In many places in Glacier Bay and
other southern coast of Alaska locations,

we have forests being
established in less than 50 years.

So let’s take a look at
some of the different types

of photography that allow us
to understand glacier dynamics.

This is a 1926 photograph
from the U.S. Navy/U.S. Geological

Survey joint photographic
reconnaissance mission.

And what’s interesting – the mission
consisted of four biplanes – see them –

you can see three of them here.
The fourth one is taking the picture.

And there were
two cameras in the biplanes.

One was a vertical camera
through a hole in the bottom.

The other was a handheld camera
weighing 60 pounds that was

located in the back of the plane.
So there was a pilot in the front seat.

There was a photographer
in the back seat.

And the photographer
was taking oblique photographs

over the side
of the open cockpit.

And collectively, these four aircraft,
between 1926 and 1929,

collected about 40,000 photographs
of southeastern Alaska.

So all the glaciers in Glacier Bay
were well-photographed by 1929.

Brad Washburn took this picture
of the Harvard Glacier, which is

one of the few advancing glaciers.
This was 1938.

Satellite imagery gives us a much more reliable
source of imagery about which we can then

make determinations of
how glaciers are changing.

So this is a map showing the locations
where Landsat images are –

Landsat is a satellite that repeats
its orbit every seven or eight days.

And so each of these
areas that’s in light purple

is a location of a scene
that has glaciers in it.

And so the way the Landsat
satellite orbits, it repeats taking images

over each of these scene centers.
And since Landsat first was established

in 1972, as I said, many of these
images – many of these glaciers

were imaged more than 500 times,
and some more than 1,000 times.

So what can we see?

Here’s an example of the Juneau
Icefield in a 1984 Landsat image.

And then here’s a sequence of
four images that NASA put together

showing the rapid retreat
of the Columbia Glacier.

Here’s its terminus in the lower part of
the center of the image. This is 1986.

It retreated about
8 miles by 1985.

Retreated another
6 miles by 2008.

And then separated into its main
branch and its west branch by 2011.

And so Landsat is a very good way
of looking at large-area change.

Landsat, unfortunately, is based on
what we call pixels, which is – which are

individual reflections from the Earth’s
surface that are 15 to 30 meters in size.

High-resolution photography has
pixels that are less than a meter.

In fact, many of them
are less than a foot in size.

So if you really are looking at detail
change, you need to have a much more

highly focused, more resolution type
of an image data set than Landsat.

But for synoptic regional change,
Landsat is an excellent tool.

So let’s look at a group
of individual photographs.

And this is what I call
photographic forensic analysis

trying to determine what
changes have occurred.

And we’ll begin with this photo of a
glacier in the Chugach Mountains that –

each of these is a cirque.
And these are remnant cirque glaciers.

At one time, the ice filled each of the
cirques and contributed to a much

larger glacier that moved down-valley
and off the bottom of the image.

But during the 20th century –
and here we’re at an elevation

of about 6,000 feet –
a little bit less than 2,000 meters –

there’s been this dramatic melting.
And you can see all of the sediment

that’s been left behind –
the different types of moraines.

This is a glacier called the Tana Glacier.
And in the 1950s, the Tana Glacier

made contact with this valley wall
that the cursor is moving along.

And the trim line, as this is called,
shows you the height of the ice.

By 2000, the glacier was stagnant,
melting away in place.

You can see all these icebergs
that are breaking off of it.

And vegetation is becoming established.
Typical of a warming environment.

This is part of the terminus
of the Malaspina Glacier.

This is glacier ice from
this carpet of vegetation here

down and below the
surface of the water.

And these are trees –
Sitka spruce, mountain hemlock,

some cottonwood, and some alder –
that, in many cases, are as much as

200 years old growing on the
surface of the stagnant glacier.

There are as many as a dozen
glaciers along the southern coast

of Alaska that support
forests on stagnant ice.

This is the Lituya Glacier shown here in
Lituya Bay in Glacier Bay National Park.

And there’s a really
interesting story here.

This line going across the valley wall
here is known as Solomon’s Railroad.

And that is the top of the
lateral moraine showing

how thick the ice was
in the 16th century.

It was about 500 meters higher
than the elevation of the bay.

This line is a scar from a huge
landslide that took place over here.

This massive rock – a million cubic
meters of rock fell into the fjord,

caused a splash wave that went up

vegetation off the side of the valley.
And this is the vegetation that’s

become re-established since that
earthquake-induced landslide in 1954.

What makes it even more interesting,
there were four fishing boats anchored

at the mouth of the bay that were
transported up and over the moraine

at the mouth of the bay as much as
4 miles into the Gulf of Alaska, and

there were survivors on two of the boats.
So there are eyewitness stories.

And that’s just one example
of some of the unusual types

of dynamics that can occur in a
tectonically active area with glaciers.

Another glacier – here’s the ice terminus.
This large moraine shows how big

the glacier had been during
its Little Ice Age maximum.

This is melting rapidly,
and you can see how quickly

the vegetation gets established in the
area that the glacier ice has vacated.

Okay. This is the last
of the single photographs.

This is a bay in front of the
Nellie Juan Glacier. This is Nellie Juan

in Prince William Sound –
western Price William Sound.

The star here is a
photographic site location.

And the next pair of images
I’m going to show you were taken

from that location
looking across – sorry –

looking across the bay here
from this point in this direction.

So the first image
was taken in 1909.

And you can see the
extent of Nellie Juan Glacier.

This is close to the edge
of that bright blue bay

that we saw in
the last photograph.

And then this is the
same location in 2011.

And here are the pair of images.
So we went from this large

tidewater terminus of a glacier
to the complete retreat out of the field

of view of Nellie Juan Glacier
in a period of 102 years.

This is a 1957 photograph looking
towards the terminus of the glacier.

And this is a 2011 re-photograph
of the same area.

And so we went from glacier sediment,
glacier bay, and bare ice,

to the complete disappearance
of the glacier ice and a coastal wetland –

a marsh – and mature trees,
all in the space of less than 60 years.

I mentioned Harvard was
one of the advancing glaciers.

It’s hard to see in this pair of images,
but this is 1938. This is 2006.

But you can see it more
clearly in a ground-based

pair of pictures that
I’ll show you next.

So this is Harvard in 1909.

And this glacier here is called Baltimore
Glacier, and you can see its extent.

This is Harvard.
And this is the tributary coming in.

This is Radcliffe.


Here is the same
location in 2002.

So we’re looking at
about 93 years of difference.

Notice Baltimore Glacier
is significantly smaller,

but Harvard has been
advancing dramatically.

Pedersen Glacier in the Kenai Fjords.

Again, bare bedrock,
glacier ice.

Same location in 2004.

But what makes this even
more interesting – these trees were

drowned when the ground surface
submerged in the 1964 earthquake.

This area went
down about 15 feet.

So between 1909, when you had glacier
ice, no vegetation, a forest developed,

and in less than 55 years, it grew and
then was killed by the earthquake.

And the area then
became a coastal marsh.

Columbia Glacier – this is a 1931
photograph. Here’s the terminus.

And it’s pushing a
moraine in front of it.

And then here we are 80 years later,
and there’s no ice to be seen anywhere

in the photograph – no glacier ice.
Just some icebergs floating.

Rapid change is characterized by
this pair of images. This is 2002.

This is South Sawyer Glacier,
which is in Tracy Arm south of Juneau.

And seven years later,
there was this massive loss of ice.

And you can see
the trim line, again,

showing what the height
of the ice had been in 2002.

This is a photograph that
Brad Washburn made in 1938.

Shows up in many textbooks. I made an
effort to duplicate this one in 2006.

And what you can see
along the valley wall here

is that the ice has thinned,
exposing, again, this trim line.

But, for the most part,
looks quite similar.

If we had looked
the opposite direction,

we would have seen that most of the
terminus of the glacier had disappeared.

Let’s move from where we were in
Prince William Sound to Glacier Bay.

Glacier Bay is one of the
more unusual well-documented

glacier retreat
sequences in Alaska.

And about 1750 A.D.,
Glacier Bay was completely filled

by a large mass of glacier ice.
Within 100 years – whoops, sorry –

the ice retreated about 30 miles,
opening up lower Glacier Bay.

And as you can see,
there’s an east arm and a west arm

because the ice is going to
continue to retreat and separate.

By 1890, the west arm was
almost completely exposed,

and the east arm was just
slowly beginning to emerge.

By the 1930s, most of
the east arm is visible.

And some of the side fjords start to
emerge in the 1960s and the 1980s.

So what does Glacier Bay
look like now?

Pretty much this blue mass with
huge amounts of vegetation

and just a few remnant glaciers,
all in the upper parts of the fjords.

What we’re going to do is look at
a sequence of about seven pairs of

photographs to document the rapid
retreat of glacier ice in the east arm.

We’re going to start with
this 1886 photograph.

And notice the way tourists dressed
to visit Glacier Bay in the 1880s.

This gentleman with his camera
has a formal coat and a top hat.

This woman has a
bustle and a fur muff.

And that’s how you went and visited
glaciers in the 1880s. [laughter]

What does that place
look like in the 21st century?

Looks like this.

So how do we know?
Well, see, this rock mass here?

There it is.

So that’s the
before and after.

So the ice has retreated more than 40
miles from this location since the 1880s.

In fact, as this diagram shows,
here is where the ice was in the 1860s,

the 1890s, and the glacier now
is way up here, and we’ll take

a look at it in a
couple of later slides.


This is one of the more fascinating
pairs that’s going to come up.

In 1961, this is the side inlet
on the west side of Muir Inlet

called Wachusett’s Inlet.
This is Plateau Glacier.

Notice the two people standing
over here on the peninsula?

Also, there’s no vegetation to be
seen anywhere. This is 1961.

43 years later,
it looks like this.

Remember the
people over here?

My two field assistants are down here,
and they are in float coats.

They couldn’t get there because
the vegetation was so dense.

So we go from this black-and-white ice
and bare bedrock environment

to this extremely well-vegetated –
almost complete absence of ice.

This is a September picture,
so the cottonwoods here

are already
changing color.

Continuing along as we
move north in the east arm.

This is a photograph I took in 1980.
I started working in Glacier Bay in 1974.

And this is the terminus
of McBride Glacier.

What did it look like just
24 years later – 23 years later?

What does it look like now?
So there is where it was in 1980.

This is where it was in
the 2003 photograph.

And here’s where it retreated by
2009 when this picture was taken.

I was fortunate to be able
to get back there two summers ago,

and I took
this picture.

And between 2009 and 2015,
it retreated another 350 to 400 meters.

The next pair of photographs
is one of the most reprinted

of all of the glacier
photographs I’ve ever taken.

Bill Field made
this photo in 1941,

and I was able to get back
to this location in 2004.

There are 2,300 feet –
vertical thickness of ice here.

Now there’s
800 feet of water.

And so notice, in 1941,
no vegetation, bedrock,

and some tightly compacted glacier till.
In 2004, dense vegetation.

In his notes, Bill Field wrote,
it’s about a 15-minute walk

up the side of this ridge
to get to the photo point.

It took us more than six hours because
we were pushing through the alder.

We had no view
of the sky.

And if we didn’t have GPS,
we’d still be looking for this location.

So here is where the terminus
of the picture was – the terminus

of the glacier was when Bill Field’s
picture was taken in 1941.

By 1950, it retreated here. By 2004,
it was another six miles off to the left.

This is a 1976 photograph I made
of the terminus of Muir Glacier.

And what’s really interesting to me –
see the algae on these two lighter bands

of igneous rock?
These are aplite dikes.

They’re intruded into
this darker bedrock.

The glacier was calving so often that
the splash waves kept this rock wet.

And at the temperatures that
were present, the marine algae

could grow about 6 or 7 meters
above the water’s surface.

In 2003, the glacier is long gone,
and the algae is long gone as well

because there is no way
it was going to be sustained.

It needed the moisture
from the splash waves.

However, the alder is
starting to get established.

So in 1976.

I did not realize when I took this picture

in 1978 that there was a 4,000-foot-high
mountain sitting right here.

But when I went back.
[laughter] There it was.

So you learn.

And I assumed this was all clouds,
but when you look closely,

you can see these jagged –
what are called arete ridge peaks in the –

in the surface of what is
a snow-covered mountain.

So this is the retreat of Muir Glacier
from being a marine tidewater glacier

onto land – you can see it’s out of
the water back here, and it’s developing

large ice blocks that are covered
by sediment – stagnant ice.

A couple of
aerial photographs.

A colleague of mine, Austin Post,
took this photo in 1986.

And I made an effort to
duplicate it from the air in 2009.

And then again in 2015.

And I apologize.
I notice I’ve got the

wrong date here,
but this is 1986, 2009, 2015.

During that period of time, the glacier
retreated onto the shoreline about 1994.

And it has been continuing
to retreat and separate.

So the two individual
termini are no longer connected.

So let’s look at that whole sequence.

Began retreating.
By 1950, it was here.

By the 1970s,
it was here.

By 1994, it retreated out
of the water.

2004, it was down here.
2015, it’s back here.


So I’m going to finish by giving you
a short summary of an ongoing project

I’m involved with looking at the
Malaspina Glacier, which is the largest

piedmont glacier in continental
North America and the largest

piedmont lobe, which is – meaning
it’s a large, flat, low-relief terminus.

It’s about 60 kilometers
across from east west –

distance of
approximately 40 miles.

And it’s made up of three major
tributaries – the Agassiz Glacier,

the Seward Glacier,
and the Marvine Glacier.

Here is the end moraine.
This is the course component that

was deposited by the glacier when it
advanced to this point in the early 1800s.

And since then, it’s been stagnating
and wasting away in place, and it’s

supporting, on top of this stagnant ice,
these 200-year-old trees.

USGS expeditions in the

In the 1970s, when I was here in Menlo
Park, one of my responsibilities was to

collect seismic data in the Gulf of Alaska
offshore of the Malaspina Glacier.

And from that data, we discovered
there were deep submarine valleys

on the continental shelf.
And I was always interested in

determining where they
went under the glacier.

And so this project I’m describing
to you is one where new geophysical

capabilities allow us,
almost on a decadal time scale,

to get more insight into
what’s happening here.

Photography shows that the glacier
surface has some major sags.

And the sags, as it turns out,
seem to correspond to places

in the bed where there are
fjords underlying the ice.

So the surface of
the glacier topography

mimics the morphology
of the glacier bed.

Here’s a Landsat image
from the 1972 time period.

And you can see how fingers of
snow fill some of these depressions.

And one of the larger depressions
actually corresponds to something

that looks like this.
A series of Landsat images show that,

based on the seasonality, the glacier
surface looks very, very different.

In winter, when it’s completely
snow-covered, you don’t see

the complex topography.
But as the snow begins to melt,

you can get some insights into where
these subglacial features are located.

This is a radar image that was
collected in 1978 of the glacier.

And it shows the loop moraines,
as they’re called,

that make up much of
the surface of the ice.

In 1986, USGS flew its own radar,
and we produced an image

that looked like this, which is very, very
different from what I had thought

a standard image of a – of a large
piedmont glacier would look like.

And what we discovered is that the surface
of the ice, as I had suggested before, was

mimicking the
morphology of the bed.

And so some of these
dark areas are the extensions

of the fjords that sit out in the
Pacific Ocean underlying the glacier.

And they extend
more than 30 miles up-glacier.

And, in some cases, their depths are as
much as 400 meters below sea level.

So depths of more than

So here’s the more traditional radar
image and this image that we collected.

So we started doing field work in the

in these troughs and
the adjacent brighter areas.

And what we discovered was
that these brighter areas –

and this is a photograph taken from this
point here, and you can see that there are

little cirques. This is the floor of
the fjord underlying the glacier.

And we discovered that
there are other places where

there were dendritic channels
on the surface of the ice.

And also, one location where we
could see part of the plate boundary

tectonic fault system exposed
as a surface sag in the glacier.

When we put our radar image and
matched it with the offshore topography,

there was a direct linkage
between the offshore large channels

and the channels that
underlie the glacier.

In the 1988 time period,
we did ice surface geophysics

and were able to measure ice
thicknesses and depths and discovered,

in some places, in the distance
of two-thirds of a mile,

the depth increased
by 400 to 500 feet.

We wrote a paper basically
summarizing what we had found

and thought we had been able to
answer all the questions we were asking.

Because we had basically
used all the capabilities

of the technologies
that were available.

Then, in 2008, and then again in 2012,
NASA was testing its Mars

ice-penetrating radar –
something that they’re going to

fly to Mars in the future –
and we were able to get a number of

new transsects across the
Malaspina Glacier’s piedmont lobe.

And when we looked at these, we were
able to see the morphology of the bed.

Also we’re able to see
how the glacier has thinned.

These are different
surface elevations.

This goes back to the 1970s.
This is the 2010 surface.

And by taking all of these transects,
lining them up, and plotting them,

what we discovered was there is a
distinct correlation between the

surface sags on the glacier and these
deep fjords underlying the glacier.

And that, in places, even though
the ice is 2/3 of a mile thick,

its surface topography mimics
the morphology of the bed.

And this has shown up
time and time again.

So two years ago,
we were able to get back

to the surface of the glacier and try a
new technology, which is 3D Lidar.

This is a Lidar – this is a photograph
showing one of these moraines

on the surface of the glacier.
This large glacial erratic sitting here.

This is the Lidar image.
So we were able to do a

high-resolution topographic map of
the surface of the ice from the Lidar.

And now we’re doing our first
analyses of these data trying to

understand how the local topography
manifests itself on different types

of radar and photographic imagery
and trying to understand, again,

in more detail, the relationship
between the surface of the ice

and the morphology
of the bed.

So I’ll stop here, and I’ll be happy to
entertain any questions that you have.

I hope that you’ve gotten an idea that,
at least in parts of Alaska, the ice is

very dynamic. Certainly the Larsen C
in Antarctica is very dynamic.

And we’re living
in an environment and a time

when glaciers are
changing rapidly.

With the major consequence being
significant amounts of melt water

making their way into the global ocean
and sea level rise becoming a reality

that we need to contend with to
understand what will happen

to places like here in California,
the Sacramento River Delta,

the Gulf of Mexico on the southern part
of the coast, all of the barrier islands

on the East Coast, and, especially in
the Pacific, all of the low-lying atolls.

So thank you
very, very much.

[ Applause ]

- [inaudible] use this?
Are you comfortable with the mic?

- Sure.
- Or you want a lapel mic, or …

- No, I’m good.
- Okay.

- Questions, please.

- And if you could – if you could make
your way to one of the microphones.

I have this little lapel mic.
This is a good substitute, but yeah,

it’s easier to line up for the
mics for the online audience.

Did you have a question?
- Yes.

- I’m amazed I’m going to be
the first one to ask a question,

but your presentation shows
that these glaciers have been

melting over the
last century, really.

What is the difference between
the melting then and the melting that

we’re now concerned about
with global warming today?

- Okay. It’s cumulative.
So when it started, we weren’t

sophisticated enough to recognize that it
was having an impact on global sea level.

Now, where we can quantify it
because we have so many more

satellite capabilities and tidal gauges
that have been placed in sensitive areas,

we can see the
rapidity of the change.

And we’re seeing that there’s actually
an acceleration in the rate of melting.

You might say, so what?
And where the really big so-what comes

in is that most of Earth’s population lives
within about 50 miles of the ocean.

And most of Earth’s infrastructure is
within that 50 miles of the ocean.

And a lot of that infrastructure is located
at elevations that are either at or,

in some cases, below sea level.
Case in point – New Orleans.

Or, I was on vacation
two weeks ago in the Netherlands

where there are many places
that are 20 feet below sea level

that are protected by these
massive boulders – these dikes.

And so, as global sea level continues
to rise, we are faced with a question.

Do we protect the infrastructure?
Because people are located there.

And if we’re going to protect it, what’s
the cost, and who’s going to pay for it?

Now, the last time that there
was a major continental glaciation,

Earth’s inhabitants
were much more primitive.

As sea level rose and fall, they would
move and follow the falling sea level,

or they would migrate with the rising
sea level. We don’t do that anymore.

We’ve got permanent
infrastructure all over the place.

So most of the retreat in Alaska
started in the middle 18th century.

In southeastern Alaska,
many, many, many glaciers

were already beginning
to retreat by 1755, 1760.

Other parts of Alaska
didn’t have retreat until later.

But, as you saw from my numbers,
the amount of glacier ice in Alaska

and all the temperate locations
on Earth is really insignificant.

It’s Greenland and Antarctica
that are critical.

If Greenland were to melt, global sea
level could go up close to 20 feet.

We are seeing more
melting in Greenland today

than has been
observed in previous years.

And when I say “more,” one of the new
phenomena in Greenland are these large

rivers of blue water flowing off of the
perimeter of Greenland into the oceans.

And coupled with that is rapid breakup
of glaciers such as the Petermann

Glacier, which lost a piece of ice
the size of Manhattan two years ago.

In Antarctica, all of the perimeter
outlet glaciers and the ice shelves –

many of the ice shelves –
are showing breakup and retreat.

Now, the ice shelves don’t
contribute to global sea level

because they’re already
floating on the ocean.

It’s water that’s in the ocean,
although it’s in solid form.

But the glaciers that are
rapidly moving into the ocean

are contributing ice
at a much greater rate.

And as the temperatures are increasing
and the water is expanding, we’re seeing

almost an exponential increase in sea
level rise in many sensitive areas.

- I have a question about –
the first photo showed northern Alaska

had virtually nothing.
- Yes.

- Zero. And this has been going on
for literally hundreds of years.

Have there been major weather
changes that have caused the retreat?

Except for the current problems.
But going back hundreds of years.

- Northern Alaska – almost all the
glaciers are in the Brooks Range.

Brooks Range has maximum
elevations of about 8,000 feet.

And gets precipitation on
the order of 5, 6, 7 inches a year.

So it’s a polar desert.
With warming temperatures,

all of the Brooks Range glaciers
are rapidly melting.

And many of the lower-elevation ones
have already completely disappeared.

The glaciers in the Brooks Range were at
their maximum size between the 15th –

and the 19th century.

And there’s been just
dramatic retreat since then.

Other questions?

- With the – with the topography you
show at the fjords under the Malaspina

Glacier, I assume that those fjords
were carved by previous glaciers.

- Correct.

- But they weren’t filled with
sediment when those glaciers retreated.

I mean, they’re still there,
as – and why is that?

And does that mean that the
mountains that are directing the

existing glaciers coming into Malaspina
have been there all these years or …

- The mountains …
- I mean, what’s all this

say about what’s
dynamically happening?

- Let’s talk about the chronology.
The tectonics that created the coast

mountains probably started

So there’s been
high topography along

the southern coast of
Alaska for 6, 7, 8 million years.

The oldest glacier – the evidence of
the oldest glaciers along the

Gulf of Alaska coast is between
2 and 3 million years back in time.

That’s based on the sediments in the
Gulf of Alaska that have been cored.

Glaciers deposit sediment underneath
them while they advance and retreat.

When glaciers melt, the significant
increase in the availability of melt water

flushes a lot of that sediment out from
the fjords into the adjacent ocean.

There’s probably a lot of remnant
sediment under the ice, but the bedrock,

which has been probably
eroded over millions of years,

maintains its configuration
and at times is filled with sediment,

and at times,
it’s filled with ice.

It’s a dynamic exchange over, you know,
a million-year-type time frequency.

In the Gulf of Alaska, you get
one of the highest sedimentation rates

of any place on Earth.
With sediment thicknesses of

several hundred meters
just during the last 10,000 years.

And that’s all the glacier sediment
that was sitting on land either on

the glaciers or under the glaciers or
adjacent to the glacier margins being

flushed out by these cycles of glacier
advance and retreat and melting.

- Yes. I have a question.

When you talk about the large
percentage of the Earth’s population …

- Yes.
- … living near the coasts or

not too far inland,
same condition of the infrastructure,

what I always wonder about is
the probable folly of people thinking

we can build sea walls
that are going to be [chuckles]

large enough to
somehow stave off that.

How should we be thinking
about these challenges?

Beyond imagining building really
taller and taller sea walls? Thank you.

- That is a critical question.
And that’s one that’s been debated for

the last hundred years, depending on
whether you own coastal property or

you’re paying taxes that are protecting
somebody’s coastal property. [laughter]

And it becomes a question – like,
in New Jersey, the cost of the

infrastructure is less than the value
of building the sea walls to protect it.

So you have to decide, you know,
when enough is enough.

And the federal government had
been subsidizing the rebuilding

of the barrier islands in the Carolinas
up until a couple years ago.

And so there is a lot of consternation
and concern as to what happens to this

massive amount of infrastructure
that needs to be protected,

assuming the projections are correct
that sea level will rise a quarter of a foot.

That will have a dramatic
impact in many places.

Miami – the highest elevation in the
city of Miami is 4 feet above sea level.

If you’ve been to New Orleans,
you know you have to walk uphill

to get to the Mississippi River.
Because it’s protected by these

large levees, and – yeah,
the city itself is lower than that.

And the highest point
in the New Orleans area

is about 20 feet
above sea level.

If you look at the maps that show
what the coast of the United States

would look like with a 1-foot
sea level rise, we lose dramatic

amounts of coastal Virginia –
even the Potomac River basin –

the tide – the tidal basin in Washington,
D.C., gets inundated by high tides.

And with a sea level rise of a foot,
parts of downtown Washington,

which originally were swamp [laughter]
will be underwater.

- But we’re going to drag it, so …


- So that’s a real –
that’s a real critical issue.

- What do you suggest can be done,
other than the movement

of people to higher ground?
Is there any other options like …

- Well, that’s a really good question
because we’ve evolved from thinking

that we could stop climate change
to a philosophy, at least in the

past administration, of what was
called mitigation and adaptation.

How do you
minimize the impacts?

And how do you deal
with the consequences?

In a coastal environment, if you’re going
to keep your coastal barrier islands in

existence, you’ve got build protection.
And that becomes extremely expensive.

Can you
relocate people?

That’s a really expensive proposition.
And there’s not available land in many

places to move tens of thousands of
people away from the coastline.

So it depends on whether
this is a government problem

or a free market individual problem.
And that has not been resolved.

Yes, please.

- I’ve got a question that’s prompted
by one of your photographs.

Is the – could you step
back just a little bit?

There’s one that shows a fjord
with a moraine right in the front of it

that’s a very pronounced moraine
that’s fairly high. Keep going.

Mostly water.

Oh, that’s not what …

So as you’re looking for it,
I’ll ask the question.

- Okay.
- It was – it’s really obvious that that –

the location of that moraine
sort of represented a point

of maximum glaciation,
at least for some –

at some point in time.
- This one?

- No. Keep – well, actually,
that’s a good one right there, yeah.

That shows a spit …
- Here’s the moraine.

- … a spit down on the – that’s
partially grown over the vegetation?

- Yes. That’s the 1900 moraine.
- Okay. So that represents a high –

our point of maximum
glaciation right around 1900.

- Yes.
- Does that represent a local

maximum point of glaciation
at that temporal point?

- In this particular case, it does.
That may have been – that location

right here may have been the entire
maximum extent for the Little Ice Age.

- Mm-hmm. So there must be
lots of evidence of that sort at

various glaciers across Alaska
and other places in the world.

- Yeah. No question.
There is.

- On figuring out the
things that happened in time,

like the Mississippi and Ohio Rivers
is when the maximum glaciation –

could you just talk about
that subject a little bit and …

- Sure. One of the major tools that
we use to try to understand the

chronology of glacier events
is called dendrochronology.

If you core into trees that are
growing on moraines and

count the number of tree rings,
and then throw in a fudge factor

of how long it took
for that tree to get established,

you can get some idea
of the age of that moraine.

There is a location in southeastern
Alaska, around the Juneau Icefield,

where a detailed study was
done probably 60 years ago.

And there, you have these sequences of
moraines where the ice would retreat,

stabilize, build a ridge, then retreat for
another decade, stabilize, build a ridge.

And a botanist went out
and cored all of these moraines,

measured the ages of the trees,
and was able to put together

a complete sequence for
four or five adjacent glaciers,

documenting the chronology
of post-1700 retreat.

And so similarly, when I told you those
trees growing on the Malaspina Glacier’s

stagnant ice were more than
200 years old, that’s because

we actually cored into the trees with
something called Sipre corer and

counted the tree rings and documented
what the age of those trees were.

So dendrochronology is one tool.
Radiocarbon dating for older glacier

events – because typically you get
organic material buried in the moraines.

And that allows you to separate
wood fragments, or sometimes shells,

and date them. It gives you an idea
of when they were deposited.

And then there are several other
techniques that have to do with

minerals like – or chemical elements
like beryllium, where, on the surface

of an exposed rock over time,
there will weathering.

And if you measure the crust of the rock
and look at the chemical composition,

you get some idea of how long
it’s been weathering in place.

So if you take those types of tools
and put them together, in many places,

you can get some kind of
a chronology that allows you

to understand the
sequence of events.

I hope that answers your question.
Yes, please?

- I’m curious what it felt like for you to 
come to these places and have that

experience of seeing the ice retreat and –
but given the scale of – the time scale

in which you work, do you think of it
sort of as this eternal change?

Or do you have an emotional
response to it when you arrive,

and it’s so
vastly different?

- In a lot of cases,
we had no idea

what we were going to
find when we got there.

And you have a photograph that was
taken by somebody in the 1880s.

And you have a
general idea of the location.

And you start saying,
well, that peak is this one.

And you say, oh my goodness.
The ice can’t even be

seen from here anymore.
And, you know, that’s fairly traumatic

when you think about the rapidity
and the dynamic of the change.

I started doing this
repeat photography in 2000.

And so I’ve been fortunate,
over the years, to get to

more than 200
different locations.

So you come – you become
pretty jaded when you start realizing

how fast and how dramatic
the extent of changes can be.

And you become very
philosophical about it,

that the Earth is dynamic,
and it’s always going to change.

And when I get really cynical, I realize
that, no matter what we as humans do

to the Earth, there will some species of
cockroach that’ll love the end product.


- Something feeds these glaciers.
I think it is snow.

And you did mention that some
glaciers actually are not receding,

but they are actually …
- Advancing.

- … growing. So when is it a matter
of temperature – I mean, temperature –

of climate being warmer,
and when is it the matter of

precipitation being higher? And sort of
what do we know about that?

- Yeah. Okay.
So the ones that are advancing typically

originate at higher elevations close to a
major water source – the Pacific Ocean.

Many of them are in
very steep valleys,

so direct sunlight is not a major
factor in causing ongoing melting.

And typically,
they have disproportionately

larger accumulation areas
than they do ablation areas.

You know, where the ice accumulates
as opposed to where it melts.

Having said that, you can have
two glaciers side by side

that are doing totally different things.
And it may be because of the

morphology of the bed.
It may be because of the fact that there’s

a slight difference in the amount of solar
energy that reaches one versus the other.

But typically, the ones that are
advancing are all within 100 kilometers

of the Pacific Ocean,
have high accumulation areas,

typically are south-flowing,
but have narrower valleys.

And some of
them fluctuate.

Some, such as the Harvard Glacier,
sat in the Pacific Ocean 1400 A.D.

Retreated a distance of more than 30 miles
until the late 18th century.

And has re-advanced
about 6 miles since then.

There are a number
of anomalous situations.

And that’s what confuses people.
So if you’re a climate denier, and you’re

looking for evidence to say this isn’t real,
you can find all sorts of exceptions.

Trying to understand the dynamics
of the exceptions is complicated.

Some of them don’t
have a logical answer.

But overall, if you look at the volume
of ice that has disappeared from the

land mass in the last thousand years,
it’s extremely significant.

And you compare what sea level is
doing now versus what it did

during the peak of the Little Ice Age
when the glaciers were significantly

larger, we’re seeing a rapid increase
in sea level in many places,

understanding that there are other
factors that influence sea level as well.

Any other questions?
- Oh, we have one more question here.

- Sure.

- You mentioned the Greenland
glaciers as being the most probable ones

of causing the maximum
sea level rise in the near future.

I mean, compared to eastern or Antarctica,
which would be terrible.

- Right.
- That’d be hundreds of feet,

but that’s not
likely to happen soon.

But the problem would be –
could you expand on that a bit more?

How fast are there –
is the Greenland glaciers going?

Are they going to cause a 1- to 3-foot
rise in the next 50 years,

or it’s only going to be 1 –
or half a foot or something?

- Yep. I showed you the IPCC figure.
Actually, let’s go back.

Okay. So the IPC says that –

7 to 23 inches, depending on where
you are on the Earth’s surface, by 2100.

Then they
have a caveat.

This does not include the
catastrophic collapse of Antarctica.

They didn’t put in Greenland because,
at the time they made their prediction

in 2013, Greenland wasn’t being
recognized as being as rapidly changing

as it seems to be in
the last four or five years.

- [inaudible]?
- Yeah.

So we just don’t know.
It’s a simple answer.

There is increased melting around
the perimeter of Greenland.

And even in the interior of Greenland,
we’re seeing melt water on the surface

that had never been observed –
you know, certainly a decade ago,

it was unknown.

Whether this is indication that the rate
of sea level change could be greater?

Stay tuned.
That’s all we can tell you.

There is concern in Antarctica with
the breakup of the ice shelves.

The ice shelves serve as a break.
They keep the glaciers that are flowing

from land into the oceans constrained.
But if you remove the floating ice

shelves, the glacier velocities can
increase, and the volume of transport

can increase, contributing to
an increase in sea level rise.

The biggest fear – and it’s not a
high probability – is what’s called

the catastrophic collapse
of the West Antarctic Ice Sheet.

The bed becomes lubricated,
and the ice starts moving really rapidly,

and thick sequences of
glacier ice move into the ocean.

People speculate about it,
but it’s not thought to be

something to fear at the moment.
- So that’d be tens of feet.

- Yes. Tens of feet.
So there’s no evidence of a past collapse

because the sediment record just doesn’t
preserve that kind of information.

But as more and more models
are being produced, some of the

models show extreme types
of failure that could accelerate

the rate of melting by a significant
fraction of an order of magnitude.

Yes, please?
- Right. I was very struck by

one of your photos that showed the old
trim lines and the terminal moraines at

the end of the last mini Ice Age, you said,
in, like, 1750 for the Muir Glacier.

I was wondering, is the glacier
community up in – of scientists up in

Alaska doing any models about the
prediction that came out

a couple years ago based on the
records from the 1970s of the

Stanford Solar Observatory –
that study I’m sure you’re

familiar with – the U.K. and
Russian scientists that predict,

with about 97% accuracy,
based on some models of the sun

that they came up with, that we’re due
for another Maunder Minimum by about,

what, 2022, and then 2030 or 2040,
so that we might see another Maunder

Minimum like that one between …
- Right.

- … 1650 and the 1700s.
- Yeah. And that has to

do with sunspot cycles and ...
- Right. It has to do with

the phase of the sun.
And the whole deal is that they –

the mathematical models
say that we’re due for one.

So we could see a big advancing.
- Could see an increase

in [inaudible] melting.
- And, I mean, based on, you know …

- Yeah. I have to admit to you,
that’s not an area that I focus on.

But I’ve read the predictions, and again,
it’s something that may prove to

be true in the future. I don’t know.
- Because I was very interested with –

when the first question from the
audience about those old fjords and

channels underneath that big piedmont
glacier you’ve been studying …

- Yep.
- Because if – my background

is more geology. [laughs]
And then also using radar –

airborne radar
through triple canopy.

So it’s very interesting to me this radar
data with the ice penetrating from Mars.

It could be that the geology is
lining up with the little mini Ice Ages

on those and that we’re just seeing –
almost seeing – if we look at the

whole picture, the stasis is, okay,
the glacier is way back here to here.

And then you add in the tectonic.
So that could explain why those

channels weren’t filled up with sediment.
- Yes. There are a couple of places along

the coast of Alaska where you can see
fjords that were hundreds of meters

below sea level now sitting exposed
2,000 feet above sea level on the valley

wall in places like Icy Bay filled with
massive younger sediment sequences.

So in a tectonically active place like
coastal Alaska, the current fjords

have to be relatively young, meaning,
you know, 1 or 2 million years old.

Because the fjords
from 6 and 7 million years ago

are now well-exposed
well above sea level.

But it’s a dynamically re-forming
environment where the glaciers

continue to erode, they form new fjords,
tectonics pushes everything up there,

or parts of Alaska, they’re going up –
coastal Alaska going up several

centimeters – you know,
good fraction of an inch a year.

Yes, please?
- I’ve been reading about,

as the glaciers melt,
the land is rising under them

because of the weight.
- The isostatic readjustment, yes.

- How significant is that?

- Give you an example.
Hudson’s Bay in eastern Canada

has risen something like 600 feet
in the last 20,000 years.

Because there were several miles
of ice that depressed the crust.

And the ice melted away,
and the isostatic readjustment

continues to cause it to elevate.
In the Little Ice Age time period,

the best example is around Gustavus,
Alaska – the mouth of Glacier Bay.

There are periods of time when some of
the rates approach 2 inches per year.

And that is because the ice
depressed the crust, the ice melted,

and the crust is now readjusting.
So that’s a reality.

There are many places
along the East Coast of the U.S.

that are still rising after being
depressed during the Pleistocene.

So if you look at coastal Maine, you see
there are numbers of glacial erosion

features that were below sea level that
are now exposed above sea level.

- What is your opinion,
or even your knowledge of –

what does this mean for the Bay Area?
By 2100?

- That’s a good question
because the Bay Area has been

so altered historically that almost
all the shorelines are artificial.

And with the Sacramento River Delta
keeping sediment from flowing

into the bay, you don’t build
new land that would allow you

to compensate
with rising sea level.

But California is tectonically
active, and it’s rising.

So when you put all those together,
I don’t think there’s going to be

a significant amount of
inundation in the Bay Area.

Coyote Creek – you know,
south end of the bay

keeps on getting flooded
more and more frequently.

But most of the
San Francisco Peninsula is bedrock

and is high and dry and
will continue to be high and dry.

So I don’t think I’m giving you a good
answer, but I don’t envision there’s

going to be that substantial a change to
Bay Area shorelines with exceptions of

all of the low sediment areas around
the southern perimeter of the bay.

- Okay. Well, again,
thank you all for your questions

and for coming [inaudible].

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