592
October 2020
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
PHOTOGRAMMETRIC
ENGINEERING &
REMOTE SENSING
J
ournal
S
taff
Publisher ASPRS
Editor-In-Chief Alper Yilmaz
Assistant Editor Jie Shan
Assistant Director — Publications Rae Kelley
Electronic Publications Manager/Graphic Artist
Matthew Austin
Photogrammetric Engineering & Remote Sensing
is the official journal
of the American Society for Photogrammetry and Remote Sensing. It is
devoted to the exchange of ideas and information about the applications of
photogrammetry, remote sensing, and geographic information systems. The
technical activities of the Society are conducted through the following Technical
Divisions: Geographic Information Systems, Photogrammetric Applications,
Lidar, Primary Data Acquisition, Professional Practice, and Remote Sensing
Applications. Additional information on the functioning of the Technical
Divisions and the Society can be found in the Yearbook issue of
PE&RS.
Correspondence relating to all business and editorial matters pertaining
to this and other Society publications should be directed to the American
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COPYRIGHT 2020.
Copyright by the American Society for Photogrammetry
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In 1750, around the time the Little Ice Age reached its maximum, Glacier Bay in
southeast Alaska was entirely filled with ice. When Captain George Vancouver
sailed there in 1795, the glacial ice had pulled back to expose five miles of the
bay—all part of a tidewater glacier’s natural life cycle of advance and retreat. By
the time naturalist John Muir explored and documented the region in 1879, the ice
front had retreated 45 miles.
Today, the ice has retreated more than 60 miles (100 kilometers), and most ves-
tiges of the original glacier now terminate on land. Just a handful of glaciers still
flow into Glacier Bay and dispense icebergs—a type of glacier known as “tidewa-
ter glaciers.” Only one—McBride Glacier—still flows into the bay’s East Arm.
The past few decades of glacial retreat are visible in the cover image, acquired on
September 6, 1986, with Landsat 5, and the image above, acquired on September
17, 2019, with Landsat 8. Snow and ice are blue in these false-color images, which
use different wavelengths to better differentiate areas of ice, rock, and vegetation.
Muir Inlet, Glacier Bay, and the surrounding land are part of Glacier Bay National
Park. Around the time the park was established in 1980, most visitors viewed its
glaciers from the vantage point of the water, where tidewater glaciers dropped
huge slabs of ice into the bay. But the retreating glaciers, many of which now
terminate on land, have changed how visitors experience the park.
“Recent retreat has been influenced by rapidly warming air and water tempera-
tures,” said Andrew Bliss, a glaciologist with the National Park Service. “In the
East Arm, all of the glaciers are retreating; in the West Arm, a few glaciers are
stable or advancing slightly.”
One of the most notable retreats has occurred at Muir Glacier, which lost its tide-
water terminus. That is, the glacier now ends on land instead of the water, where
it once calved some of the park’s most impressive icebergs.
“This retreat caused a major change in visitation patterns,” said Tania Lewis, a
wildlife biologist and research coordinator at the park. Prior to the late 1980s, Muir
Glacier was the main destination for visitors who wanted to view calving glaciers,
icebergs, and the bay’s wildlife.
Southeast of Muir Glacier, McBride is the last tidewater glacier in the bay’s East
Arm and the only remaining source of icebergs in this part of the bay. But that
glacier is continuing to retreat. In 1998, Lewis spent six weeks near the terminus
of McBride Glacier, where she studied harbor seals. “At that time, the inlet was
only about a mile long and usually full of ice on which harbor seals hauled out,
gave birth, and nursed their pups,” Lewis said.
The inlet leading to McBride Glacier now measures more than three miles long. “I
went into McBride Inlet again last summer for the first time in over 10 years and
was blown away by how far back it was, and how long the newly exposed inlet
is,” Lewis said. During that visit she saw one large iceberg with some harbor seals
on it. “Once McBride Glacier is grounded and is no longer tidewater, there will be
no ice habitat left for seals in Muir Inlet.”
The changes to the park’s tidewater glaciers are dramatic, providing visitors
and scientists with a stark view of how ecosystems respond to ice retreat and a
changing climate.
For more information or to see both images in their entirety, visit
.
visibleearth.nasa.gov/view.php?id=147171.
