Information on the postglacial-variation history is being revealed by on-going geological interpretation. For the past 1,100 years (historical time in Iceland; settlement began in ca. 874) information can be derived from old manuscripts both directly and indirectly. Danish plane-table mapping (map scales of 1:50,000 and 1:100,000) was carried out during the years 1903-1938, giving reliable information on the position of termini of many outlet glaciers, especially in southeastern Iceland in 1903-1904.

In the year 1930, Jón Eyþórsson began a systematic program of monitoring the frontal variation of selected glaciers. The program started by him has been expanded since that time and now includes 41 glaciers and outlet glaciers at 55 different locations.

Oblique aerial photographs have been obtained since 1937 by geodetic institutes and private persons. Ground-based data and datable photographs are found in various private collections and archives, including the Iceland Glaciological Society.

The U.S. Army Air Force, in association with the U.S. Army Map Service (AMS) acquired almost complete coverage of Iceland with vertical overlapping (stereo) aerial photographs in 1945 and 1946; in 1956 and 1959-1961, the U.S. Air Force rephotographed most of Iceland in cooperation with the AMS and the Iceland Geodetic Institute (Landmælingar Íslands). Landmælingar Íslands has been taking vertical aerial photographs of various areas beginning in 1952. According to a coverage plan of LÍ, glaciers are supposed to be rephotographed every 10 years, but this is usually not the case. Information on the aerial photographic archive of Landmælingar Íslands can be obtained through their Remote Sensing Division.

Icelandic glaciers have been imaged by the Landsat (1-5) satellites since September 1972. Previous to that there may be existing classified satellite images, and photographs archived by intelligence agencies. Over time, additional spacecraft acquire data that are useful for glaciological information.

Mass balance of Icelandic glaciers was first carried out in the 1930's by the Swedish-Icelandic Expedition; it established a winter balance of 5 m water equivalent or more in the upper part of the accumulation area in the eastern part of the Vatnajökull ice cap. The summer balance at the terminus proved to be in some cases about -12 m water equivalent. Winter balance has been measured yearly by the Iceland Glaciological Society since 1954 in the Grímsvötn caldera in the west-central part of Vatnajökull.

Regular pit and stake mass-balance measurements have been carried out on the northern side of Hofsjökull since 1988 and likewise on the Þrándarjökull since 1991. Profiles of mass balance (pit and stake) have been established on the eastern and south-western side of Hofsjökull since 1989. Similar profiles have been assessed on the Tungnaárjökull, Dyngjujökull, Köldukvíslarjökull and Brúarjökull outlet glaciers of Vatnajökull since 1992 and the Eyjabakkajökull outlet glacier since 1991.

Glacier variations in Iceland have been recorded systematically since the 1930's on 23 different outlet glaciers and other types of glaciers. Since that time, 18 more glaciers have been added to the monitoring system for Icelandic glaciers.

Twelve of the referenced glaciers are surge-type glaciers with virtually no indication of climatic control between surges. In the data set, 24 of the glaciers show little indication of surges and 4 are of uncertain or mixed character. The advance/retreat of some of the non-surging glaciers is intimately related to the climate with reaction at the terminus most of the time occurring well within five years from a postulated change in mass balance. The rise of the mean summer temperature by approximately 0.6ºC from the first to the second quarter of the 20^th century resulted in a rapid retreat of all measured glaciers in Iceland for the first 20 years of the measurement period, interrupted only in very few cases, mainly by surges. A turning point occurred around 1970 when most of the non-surging glaciers stopped retreating and many of them started to advance. Some of the glaciers have been advancing continuously since.

Since about 1970, the glaciers in the southernmost part of the country have regained about half of the ground lost since 1930, in the north about one third, in the west the recovery is about one quarter. In the southeast, some of the glaciers have been stationary for 30 years, while the easternmost ones have retreated slightly. Surge-type outlet glaciers with surge periods varying between 10 and 80 years are represented in the data set. In the period 1991-96 11 outlet glaciers have surged. [an error occurred while processing this directive]