Landsat 7 Glacier Inventory

PROJECT OF THE GAGE WORK GROUP
James S. Aber & Andrew G. Klein

Table of Contents
Introduction Equatorial--Tropical
Northern--Arctic Southern--Temperate
Northern--Temperate Contributors

Introduction

Glaciers and ice caps occupy about 10% of the Earth's continental area today. They interact with the atmosphere, hydrosphere and lithosphere on time spans ranging from hours to millenia. Glaciers are, thus, key components of the Earth's environmental system.
GAGE work group of the INQUA Commission on Glaciation was invited to submit glaciers and ice caps for consideration to include in the Landsat 7 global archive. These glaciers will be considered because of their potential for scientific studies on global change.

Glaciers and ice caps have experienced negative mass balances and have been retreating since the end of the Little Ice Age in the late 19th and early 20th centuries. This is a general condition for glaciers of all types in nearly all geographic locations, with the possible exception of Antarctica. The local timing of deglaciation may vary considerably, however, depending on many factors as detailed below.

Comparison of Response Rates for
Glaciers in Different Settings
Rapid Response Slow Response
High altitude (mountains) Low altitude (lowlands)
Continental interiors Maritime (islands and coasts)
Small glaciers & ice caps Large glaciers & ice caps
Mid-latitude (temperate) High & low latitudes (polar & tropical)
Atlantic Ocean regime Pacific Ocean regime
Northern hemisphere Southern hemisphere

The end of the Little Ice Age occurred earliest--mid-1800s--for interior mountains of northern mid-latitudes, such as the European Alps, and took place latest--early 1900s--on islands of the South Pacific, as in New Zealand. The end of the Little Ice Age is just beginning to have an effect in Antarctica. Meanwhile, the late 20th century has been a period of positive mass balance and expansions for small glaciers in many places, for example Iceland and Norway. Since the end of the Little Ice Age, glaciers have experienced many lesser periods of ice advance and retreat that happened at different times in separate parts of the world. This scenario indicates that global climatic change takes place with distinct regional variations. These are probably the results of lag effects caused by differences in heat transfer and storage for the Earth's surface.

This brief overview suggests complex and as yet poorly understood relationships between climatic events and glacier dynamics on a global basis. A major goal of NASA's Mission to Planet Earth program is to better document earth-surface processes, in this case glaciation, and link them to climatic data and other environmental factors. This approach, global and systematic in scope, will form the solid basis for improved understanding of the Earth's complex environmental system. This project represents an extension of the Satellite image atlas of glaciers. The atlas is based mainly on imagery from Landsats 1, 2 and 3 in the 1970s. It contains a baseline of remotely sensed data on glaciers worldwide, for which future imagery could be utilized to demonstrate changes in glacier environments.

The following glaciers have been submitted to NASA for inclusion in the Landsat 7 long-term image archive. The mandate for this proposal includes all parts of the world, except for the United States and Antarctica, which are scheduled for full coverage under other programs. Landsat path/row positions and approximate latitude/longitude coordinates are identified for each area. Brief descriptions of glaciologic and climatic conditions are given for all sites, along with additional information in some cases. Send your comments to the proposal authors, J.S. Aber (aberjame@emporia.edu) or A.G. Klein (klein@geog.tamu.edu).


Red squares denote sites described in this proposal. Dark blue squares
are additional glacier sites included in the Landsat 7 planning list.

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Northern--Arctic

Compiled by James S. Aber

Glaciers in Arctic locations generally have fairly simple climatic regimes, in which accumulation of snow takes place during a long winter season and melting (ablation) happens during a very short summer. Glaciers that advance into water bodies--seas or lakes--may also lose mass by calving icebergs. Although this may take place throughout the year, most icebergs are calved during summer, when glacier velocity is generally greatest. Dynamic activity of Arctic glaciers depends to a large extent on precipitation and accumulation rates. In relatively moist regions subject to the Gulf Stream--Greenland Sea and Barents Sea, glaciers tend to be fairly active. For drier parts of the Arctic region, accumulation rates are low and glacier activity is reduced.

For glacier mass-balance and global-change studies, the most appropriate time for acquiring Landsat imagery would be near the end of the ablation season--summer and early autumn. The optimum timing varies with latitude and local climatic conditions, but is generally only about two months in length. Unless stated otherwise, August and September are considered best months for glacier imagery in Arctic environments. Late winter imagery (March-April) is also feasible because of frequent dry, clear air and high contrast between snow/ice and bare ground or open water. Such images depict landscape and glacial topography in startling detail.

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Northern--Temperate

Compiled by James S. Aber

Glaciers in northern temperate locations (app. 40° to 65°N latitude) generally have fairly simple climatic regimes, in which accumulation of snow takes place during a long winter season and melting (ablation) happens during a short summer. Glaciers that advance into water bodies--seas or lakes--may also lose mass by calving icebergs. Although this may take place throughout the year, most icebergs are calved during summer, when glacier velocity is generally greatest. Dynamic activity of glaciers depends to a large extent on precipitation and accumulation rates. In relatively moist regions subject to maritime influence, glaciers tend to be fairly active. For drier continental interiors, accumulation rates are lower and glacier activity is reduced.

For glacier mass-balance and global-change studies, the most appropriate time for acquiring Landsat imagery would be near the end of the ablation season--summer and early autumn. The optimum timing varies with latitude and local climatic conditions, but is generally only about 2-4 months in length. Unless stated otherwise July, August and September are considered best months for glacier imagery.

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Equatorial--Tropical

Compiled by Andrew G. Klein & James S. Aber

In broad meteorological terms, the tropics extend from 30°N to 30°S latitudes. Because of fundamental climatic differences, tropical glaciers differ considerable from glaciers in higher latitudes--temperate or polar climates. The seasonal dynamics of tropical glaciers are more complicated in particular. Tropical glaciers are confined at present to high altitudes, generally > 4000 m. Many glaciers are located in the Andes Mountains of Peru and Bolivia as well as the Himalayas of India, China and Nepal. Tropical glaciers are found in other parts of South America, Africa, Asia, and Irian Jaya.

Across the tropics, glaciers have been in a state of retreat since the late 1800s. Short-term mass-balance studies have been conducted on glaciers in many locales; however, very few long-term studies are available. Tropical glaciers present both potential problems and exciting opportunities for remote-sensing glaciology. They represent key indicators for climatic conditions of crucial importance for global-change investigations. Because of their relatively small size and tenuous climatic circumstances, tropical glaciers may display significant changes in response to small variations in climatic conditions. Some are in danger of disappearing within the next several years or few decades.

For tropical glaciers, the diurnal temperature variation usually exceeds the seasonal range. Melting can occur anytime during the year, but precipitation is strongly seasonal in many cases. Seasonal precipitation is determined by north-south migration of the Intertropical Convergence Zone (ITCZ). Depending on the positions of glaciers, rain/snowfall may occur throughout the year, or in one or two distinct wet seasons. In many places, summer is the wet season, so glacier accumulation and ablation periods coincide. These seasonal dynamics, coupled with our limited understanding of glacier mass balance in most cases, preclude designing a temporal observational strategy for Landsat 7. Observations throughout the year are necessary to capture the seasonal dynamics of tropical glaciers. This means acquiring a limited number of sites with high temporal frequency (3-4 per year). Cloud-free conditions will be the limiting factor for archiving tropical glacier scenes.

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Southern--Temperate

Compiled by James S. Aber

The southern temperate climatic zone resembles the northern temperate zone, except of course the seasons are shifted by half a calendar year. The major difference is the greater oceanic mass, which exerts a strong moderating effect on climate in the southern hemisphere. Seasonal transitions may be delayed somewhat by the maritime influence, and overall seasonal contrast may be reduced compared to equivalent northern latitudes. As in the north, best times for acquiring Landsat imagery are presumably the summer and early autumn months, January-April, although the seasonal regimes of many glaciers are uncertain.

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Related Information

Satellite image atlas of glaciers
Landsat 7 program

List of Contributors

James S. Aber (aberjame@esumail.emporia.edu)
Jan Boelhouwers (janboel@artso.uwc.ac.za)
Chris D. Clark (C.Clark@sheffield.ac.uk)
Garry Clarke (clarke@geop.ubc.ca)
Archie Dyke (adyke@gsc.nrcan.gc.ca)
Robert J. Fulton (fulton@gsc.NRCan.gc.ca)
Jim Garvin (NASA Goddard Space Flight Center)
Douglas Grant (dgrant@NRCan.gc.ca)
Ole Humlum (oh@geogr.ku.dk)
Andrew G. Klein (aklein@glacier.gsfc.nasa.gov)
Fritz Koerner (kroener@gsc.nrcan.gc.ca)
Jim Peterson (Jim.Peterson@arts.monash.edu.au)
Joan Ramage (ramage@geology.geo.cornell.edu)
Martin Sharp (Martin.Sharp@UAlberta.CA)
Oddur Sigurðsson (osig@os.is)
Chris Smart (smart@sscl.uwo.ca)
Richard S. Williams, Jr. (rswilliams@usgs.gov)
Jaap Jan Zeeberg (jzeebe1@uic.edu)

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Landsat 7 GAGE project. Return to GAGE homepage.
Posted 1997; last update 2001.