704
October 2019
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 Society for
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Maryland 20814-2144, including inquiries, memberships, subscriptions,
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493-0290; the fax number is 225-408-4422; web address is
.
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Volcanoes have a lot of dramatic ways to announce their presence: thick plumes of
ash and steam; rivers and lakes of molten lava; rockfalls and lahars; earthquakes;
even the sudden rising of an island above the water line. One of the more subtle and
rarely observed displays is the pumice raft.
Many of the world’s volcanoes are shrouded by the waters of the oceans. When
they erupt, they can discolor the ocean surface with gases and debris. They also can
spew masses of lava that are lighter than water. Such pumice rocks are full of holes
and cavities, and they easily float.
On August 13, 2019, the Operational Land Imager on Landsat 8 acquired natural-col-
or imagery of a vast pumice raft floating in the tropical Pacific Ocean near Late Island
in the Kingdom of Tonga. NASA’s Terra satellite detected the mass of floating rock
on August 9; the discolored water around the pumice suggests that the submarine
volcano lies somewhere below. By August 13, the raft had drifted southwest. As of
August 22, the raft had moved north again and was a bit more dispersed, but still
visible.
The Volcano Discovery web site reported that it received an email from a sailor on
August 7, 2019, about clouds of smoke on the horizon in the direction of Fonualei
volcano. According to a bulletin from the Smithsonian’s Global Volcanism Program
(GVP), sailors began reporting sightings of the pumice raft by August 9. The crew
of the catamaran Roam encountered the pumice and provided a detailed report on
Facebook on August 15. The sailors described a “rubble slick made up of rocks from
marble to basketball size such that water was not visible,” as well as a smell of
sulfur.
Volcanologists at the Smithsonian believe the evidence points to an unnamed sub-
marine volcano near Tonga at 18.325° South, 174.365° West. The last report of an
eruption at the site occurred in 2001, and the summit of the seamount is believed to
stand about 40 meters (130 feet) below the water line.
Volcanologist Erik Klemetti of Denison University wrote: “Pumice rafts can drift for
weeks to years, slowly dispersing into the ocean currents. These chunks of pumice
end up making excellent, drifting homes for sea organisms, helping them spread...
The erupted pumice means this volcano erupts magma high in silica like rhyolite.”
For more information, visit
.
NASA Earth Observatory images by Joshua Stevens, using Landsat data from the
U.S. Geological Survey. Story by Michael Carlowicz.
