CHAPTER
18
Remote sensing of mountain glaciers and
ice caps in Iceland
Oddur SigurMsson, Richard S. Williams, Jr., Sandro Martinis, and Ulrich Münzer
ABSTRACT
In 2000, Iceland’s glaciers covered 11,079 km 2 , or
10.7% of its contiguous area. There are 269 named
glaciers, including 14 ice caps with 109 associated
outlet glaciers, 8 ice flow basins, 55 cirque glaciers,
73 mountain glaciers, and 5 valley glaciers. Twentyone surge-type glaciers have been documented. The
superposition of ice caps on active volcanoes and
associated rift zones within the neovolcanic zones of
Iceland produces aperiodic jökulhlaups. Jökulhlaups also result from the failure of ice dams on
ice-marginal lakes.
In association with Icelandic scientists, airborne
thermal infrared surveys of some glaciers were carried out in 1966, and, in 1974, the first analyses of
satellite images of glaciers in Iceland were published. Icelandic scientists began radio-echo sounding to determine the thickness of ice caps in 1976.
The start of systematic, annual field measurements
of the fluctuations of Iceland’s glaciers were begun
in 1930; now in the 21st century, between 40 and 50
termini are being measured annually. Systematic
instrumental measurements of meteorological variables were started in the 19th century at a few
coastal stations, and later expanded to a nationwide
network. On September 8, 1972 the first mediumresolution satellite images (ERTS-1/Landsat-1) of
Iceland’s glaciers were acquired; subsequently, a
variety of imaging and nonimaging sensors on
different polar-orbiting satellites have provided
aperiodic coverage of Iceland’s glaciers.
Long-term sets of glaciological data, whether
compiled from sequential map series, ground observations (termini fluctuations), and other ground
measurements (mass balance studies) or from
analyses of data acquired by satellite sensors, such
as Landsat MSS, RBV, TM, ETMþ, OLI, Seasat
radar, Terra ASTER, and ICESat GLAS, have
successfully documented changes in the area and
mass balance (volume) of Iceland’s glaciers. Glacier
variations, when correlated with changes in climate,
show a close correspondence for more than 100
years of observation. Since the mid-1990s, in
response to a warmer climate, most of Iceland’s
glaciers have been undergoing an annual average
shrinkage of about 0.3%. Except for glacier ice at
the highest elevations, at the present rate of shrinkage, Iceland may be deglacierized by 2200.
18.1
INTRODUCTION
18.1.1 History of mapping Iceland’s
glaciers
The earliest Norse settlers in Iceland (about 874 ad)
brought their knowledge of glaciers ( jökull ) with
them from their experience with glaciers and glacial
rivers in Norway, such as Hardangerjökulen and its
410
Remote sensing of mountain glaciers and ice caps in Iceland
Figure 18.1. Landsat 5 Thematic Mapper image mosaic of Iceland (vegetation image) showing the distribution of
glaciers (white), vegetation (green), lightly vegetated or unvegetated areas, including bare rock and sediment
(various shades of brown), and water (blue). Used with permission: & National Land Survey of Iceland (from fig.
1B in Sigurdsson and Williams 2008a, p. 4).
associated glacial rivers flowing into Eidfjord. Some
of Iceland’s glaciers (Figs. 18.1, 18.2) first appeared
on maps in the 16th century (Sigurdsson 1978), and
descriptions of its glaciers were included in several
books published in the 18th century (see Thorarinsson 1960 and historical review in Williams and
Sigurdsson 2004), including the first map of an outlet glacier, Sólheimajökull, by Árni Magnússon in
1704/05 (Thorarinsson 1960).
Gunnlaugsson (1848) published the first comprehensive map of Iceland, which showed the geographic location of its major ice caps. The Danish
General Staff (later Danish Geodetic Survey) began
planetable mapping of Iceland, including its
glaciers, in 1902 (Bödvarsson 1996), but the mapping was not completed before the onset of World
War II. From the end of World War II until the late
1980s, the U.S. Department of Defense, in coopera-
tion with the Iceland Geodetic Survey (Landmælingar I´slands), published several series of maps at
various scales of Iceland, including complete coverage at 1:50,000 scale in Series C762 and 50% coverage in the latest Series C761. The Iceland Geodetic
Survey (now called the National Land Survey of
Iceland) continued to publish maps at various scales
until 2006 when the NLSI stopped publishing maps,
and the only complete coverage of Iceland by them
is at a scale of 1:250,000.
18.1.2 Scientific analysis of
Iceland’s glaciers
Sveinn Pálsson’s pioneering work on Iceland’s
glaciers, which was completed in 1795, is the first
comprehensive scientific treatise on glaciers for an
entire country (Williams and Sigurdsson, 2004).
Introduction
411
Figure 18.2. Map of the eight regional glacier groups in Iceland (from fig. 1A in Sigurdsson and Williams 2008a,
p. 4).
The geologist/glaciologist Thoroddsen (1892, 1906,
1911) published several comprehensive works on
Iceland’s glaciers during the latter part of the
19th century and the early part of the 20th century.
The Icelandic geologist/glaciologist Thorarinsson
(1943) reviewed fluctuations of glaciers in Iceland
during the past 250 years and published many
papers and books on its glaciers until his death in
1983; Thorarinsson (1958), using Danish Geodetic
Survey maps, also measured the area of Iceland’s
largest glaciers.
Eythorsson (1963), a meteorologist/glaciologist,
began the first annual measurements of glacier termini in 1930, which he compiled each year until his
death in 1968. The hydrologist/glaciologist Rist
(1976) continued the annual compilation until his
retirement in 1987; since then, Sigurdsson (1998)
has continued the compilation annually. The result
of 80 years of annual field measurements of the
fluctuations of glaciers, conducted by scientists
and volunteers, has been an annual compilation
in Jökull for 60 years (Jón Eykórsson, Sigurjón
Rist, and Oddur Sigurdsson, 1951–present). With
these works, Iceland has an excellent long-term
database of glacier fluctuation, and it continues;
in 2009, 40–50 glacier termini were measured at
various field locations. Additional information
about the glaciers of Iceland has been summarized
by Thorarinsson (1975), Björnsson 1979, Rist
(1985), Björnsson and Pálsson (2008), Sigurdsson
and Williams (2008a), and Björnsson (2009).
18.1.3 Air and spaceborne imaging and
remote-sensing analysis of
Iceland’s glaciers
Airborne remote sensing of Iceland’s glaciers was
begun in the 1930s (vertical and oblique aerial
photographs) (Nørlund 1944) to support the Danish topographic mapping program in Iceland
(Bödvarsson 1996). In the mid-1940s, mid-1950s,
and early 1960s, the U.S. Army Air Force (U.S.
Air Force after 1947) carried out systematic aerial
photographic surveys to support a 1:50,000-scale
412
Remote sensing of mountain glaciers and ice caps in Iceland
series topographic mapping program, in cooperation with the Iceland Geodetic Survey. In 1966 the
U.S. Air Force (Air Force Cambridge Research
Laboratories), in cooperation with the U.S. Geological Survey and several Icelandic scientific institutions, carried out airborne thermal infrared
surveys of volcanic and geothermal areas in Iceland
(Friedman et al. 1969), including the area around
Kverkjökull, an outlet glacier in northern Vatnajökull (Friedman et al. 1972).
On September 8, 1972 the first Landsat MSS
images of Iceland’s glaciers were acquired, including an image of the partially cloud-obscured terminus of Skeidarárjökull and the southern part of
Öræfajökull and several of its outlet glaciers. The
USGS (1976, 1977) published the first Landsat
image maps of Iceland, including a fall and winter
image of Vatnajökull.
Images from the Landsat 1–5, 7, and 8 series of
spacecraft (1972–present), including images from
the Multispectral Scanner (MSS), Return Beam
Vidicon (RBV), Thematic Mapper (TM), Enhanced
Thematic Mapper (ETMþ), and Optical Line
Imager (OLI) sensors have been used by many
glaciologists to analyze surficial glaciological and
subglacial (tectonic and volcanic) features and
changes in the ice caps and associated outlet glaciers
of Iceland, with particular emphasis on Vatnajökull
and its outlet glaciers. Analysis of a low solar-elevation-angle (less than 6 ) Landsat image of Vatnajökull (U.S. Geological Survey, 1977) provided new
information about subglacial tectonic and volcanic
features (Thorarinsson et al. 1974). Other Landsat
images provided information about glaciological
features (Williams 1986a, b, 1987), including glacier
facies (Williams et al. 1991), the Brúarjökull outlet
glacier (combined with ERS-1 SAR data) (Hall et
al. 1995), and a comparison of satellite image versus
ground-based measurement of fluctuations of several outlet glaciers (Williams et al. 1997). Landsat
images and maps were used to do a preliminary
glacier inventory of the Langjökull Group of glaciers (Williams 1986b).
Four satellite image mosaics of Iceland, using
image data from four different sensors, have been
compiled: a Landsat-1 MSS image mosaic in 1974, a
Seasat radar mosaic in 1978, a Landsat-5 TM
mosaic in 1993, and a SPOT-5 mosaic in 2006.
Areas of Iceland’s glaciers were measured on Landsat images and ancillary sources by Björnsson
(1978a), Williams (1983), and Sigurdsson and Williams (2008b) (Table 18.1). Additionally geodetic
airborne laser altimeter surveys were made of
Skeidarárjökull and Breidamerkurjökull (Garvin
and Williams 1993); ICESat GLAS profiles of the
Drangajökull ice cap were compared with April
2003 GPS ground survey profiles (Shuman et al.
2008). Airborne LiDAR mapping of Iceland’s ice
caps and mountain glaciers was begun in 2008 and
continues (Jóhannesson et al. 2013).
18.2
REGIONAL CONTEXT
18.2.1 Geography and geology
Iceland, a glacierized volcanically active island, is
situated in the North Atlantic Ocean between
Greenland’s Blosseville Coast located about 280
km to the northwest with the Færoe Islands and
Shetland Islands of Scotland lying about 425 km
and 700 km, respectively, to the southeast. The
island has an area of 103,000 km 2 , and is centered
at about 65 N latitude and 19 W longitude; except
for the northern part of the island of Grı́msey, Iceland lies south of the Arctic Circle. About 10.7% is
covered by glaciers, with most of the glacierized
area (97%) contained in the six largest ice caps
and associated outlet glaciers (Figs. 18.1 and 18.2,
Table 18.1). Björnsson and Pálsson (2008) calculated the volume of ice in Iceland’s glaciers to be
3,600 km 3 .
Iceland is the largest island on the Mid-Atlantic
Ridge; it also straddles the transverse Greenland–
Færoes Ridge, which extends from Greenland to
Ireland. The island sits astride tectonically active
rift zones, characterized by frequent subaerial, subglacial, and submarine volcanic eruptions and
earthquakes sourced along the plate boundary
between the North American and Eurasian Plates.
Transform faults are located in southwestern
Iceland (Southwest Fracture Zone) and northern
Iceland (Tjörnes Fracture Zone). Extending to the
southwest from Iceland is the submarine Reykjanes
Ridge; extending to the north of Iceland is the
submarine Kolbeinsey Ridge (also known as the
Iceland–Jan Mayen Ridge).
The oldest volcanic rocks in Iceland are Miocene
in age; they are located in the dissected plateau
basalts of the western (maximum age 16 Myr),
northern (maximum age 12 Myr), and eastern
(maximum age 14 Myr) parts of Iceland. Active
zones of tectonic rifting and effusive volcanism
are situated between the older plateau basalts
including a western neovolcanic zone, an extension
onshore of the Reykjanes Ridge, which stretches
Regional context 413
Table 18.1. Area of Iceland’s glaciers from analysis of aerial photos and satellite images.
Glacier name
Area
(km 2 Þ
Image source
Year
Vatnajökull ice cap
8,086
Landsat 7
2000
Langjökull ice cap
920
Landsat 7
2000
Hofsjökull ice cap
889
Vertical aerial photo
1999
Mýrdalsjökull ice cap
597
Vertical aerial photo
1999
Drangajökull ice cap
146
SPOT-5
2004
Eyjafjallajökull ice cap
80
Vertical aerial photo
2003
Tungnafellsjökull ice cap
38
Landsat 7
2000
Rórisjökull ice cap
30
Landsat 7
2000
Eirı́ksjökull ice cap
22
Landsat 7
2000
Tindfjallajökull mountain glacier
15
SPOT-5
2000
Torfajökull mountain glacier
11
Vertical aerial photo
1999
Rrándarjökull ice cap
17
SPOT-5
2000
Snæfellsjökull ice cap
12
Ground measurements
2002
Hrútfellsjökull ice cap
7
Landsat 7
2000
Hofsjökull eystri ice cap
5
SPOT-5
2000
Okjökull mountain glacier
4
Landsat 7
2000
North Iceland glaciers
179
SPOT-5
2004–2006
East Iceland glaciers
13
SPOT-5
2003
Other glaciers
8
Total
11,079
beyond the northern end of Langjökull ice cap. The
eastern neovolcanic zone extends in a northeasterly
direction from Surtsey, Heimaey, and other islands
in the Vestmannaeyjar Archipelago to the northern
side of Vatnajökull and from there, as the northern
neovolcanic zone, in a northerly direction to the
north coast of Iceland.
Two active major central volcanoes, Hofsjökull
and Öræfajökull, are situated outside the rift zones.
In western Iceland, an east to west-trending active
zone of volcanism is separated from the other neovolcanic zones (Sæmundsson 1980; Thorarinsson
and Sæmundsson 1980). The major historic centers
of volcanism and rifting created topographically
higher regions upon which the four largest of
Iceland’s ice caps (Vatnajökull, Langjökull, Hofsjökull, and Mýrdalsjökull) are located (Figs. 18.1
and 18.2). The average elevation of Iceland is 500 m
above mean sea level; a nunatak on Öræfajökull, an
internal ice cap contiguous with Vatnajökull, is the
highest point on the island at 2,110 m. Subglacial
volcanism during the Pleistocene created mountains
upon which four additional ice caps are situated
(Tungnafellsjökull, Rórisjökull, Eirı́ksjökull, and
Hrútfellsjökull) (Figure 18.2). Three ice caps lie
outside the neovolcanic zones, one in the northwest,
414
Remote sensing of mountain glaciers and ice caps in Iceland
Drangajökull, and two in the southeast,
Rrándarjökull and Hofsjökull eystri. One ice cap,
Snæfellsjökull, lies on the western edge of the east to
west-trending volcanic zone in western Iceland.
The majority of Iceland’s glaciers are mountain
glaciers, and most of these are cirque glaciers situated in the dissected plateau basalts of the Tröllaskagi area of northern Iceland to the west and
southwest of Eyjafjördur (Fig. 18.2; Sigurdsson
and Williams 2008a). The location of the four largest ice caps (and some other ice caps and mountain
glaciers) within the neovolcanic zones creates conditions under which aperiodic subglacial volcanic
activity is followed by glacier outburst floods
(jökulhlaups), especially from subglacial calderas
and associated rift zones within the margins of
Vatnajökull and Mýrdalsjökull (Fig. 18.2). Glaciological hazards in Iceland, including both types of
jökulhlaups, volcanic and lacustrine, and surgetype glaciers, will be addressed in more detail later
in this chapter.
18.2.2 Climate and climate variability
The climate of Iceland was described in the modified Köppen classification as comprising two categories, ‘‘polar’’ for the northern third of the island,
and ‘‘humid’’ maritime temperate, with no dry season and a short cool summer for the southern two
thirds (see de Blij et al. 2004, their fig. 16.3, pp. 206–
207). The northern one third can be better characterized, however, as ‘‘humid microthermal’’ (deBlij
et al. 2004). The variability of seasonal temperature
and precipitation for the island is governed by the
convergence of polar air masses from the northwest
and initially tropical now-temperate air masses
from the southwest. Warm Gulf Stream waters
flowing north-northeast in the North Atlantic
Ocean turn to the east-northeast south of Iceland,
with one branch (Irminger Current) turning to the
north-northeast to flow clockwise along the western, northern, and eastern coasts and the other
branch flowing to the northeast over the submarine
ridge between Iceland and the Færoe Islands.
Intense low-pressure systems periodically travel
along the fluctuating frontal boundary between
the polar and temperate air masses, producing rainfall in summer and snowfall in winter, with the
greatest precipitation occurring in southern Iceland
and a tenfold reduction in the highlands north of
Vatnajökull. For example, annual precipitation on
the higher southern slopes of Vatnajökull, Mýrdalsjökull, and Eyjafjallajökull can exceed 4,000 mm
(Crochet 2007); in the ‘‘rainshadow north of Vatnajökull in the Ódádahraun, annual precipitation
can be less than 400 mm. Virtually all of the ice caps
receive an annual precipitation total greater than
2,000 mm. Storms that pass south of Iceland bring
colder temperatures in the polar air mass side of the
frontal boundary; storms that pass to the north
between Greenland and Iceland bring milder temperatures in the temperate air mass side of the
frontal boundary. Polar pack ice and icebergs carried southwest along the east coast of Greenland in
the East Greenland Current can sometimes be carried in an east-flowing branch which moves along
the northern coast of Iceland, and, although rare
historically under conditions of severe pack ice concentration, can move south along the east coast of
Iceland (Thorarinsson 1975). Both Thoroddsen
(1916–17) and Grove (1988) used sea ice as a ‘‘proxy
record of past climate during historic time in
Iceland (since about 874 ad). Grove (1988) was
particularly interested in relating sea ice conditions
north of Iceland to glacier advances during the
Little Ice Age.
Accurate meteorological observations were
begun at a few sites in the early 19th century (Williams and Sigurdsson, 2004). By the latter part of
the 19th century, an extensive network of meteorological stations had been established at various
ports, and extended later into the settled interior
of Iceland and at airfields. As a result of this comprehensive record of meteorological variables, the
climate of Iceland can be accurately determined
since the late 19th century, which corresponds with
the end of the Little Ice Age, and which also marks
the maximum extent of glacier advance during
that period (Sigurdsson 2005). Eythorsson and
Sigtryggsson (1971) and Einarsson (1976, 1984)
have analyzed these data and described changes
in the climate of Iceland. Ólafsson et al. (2007), in
an editorial, summarized the climate of Iceland:
mean annual temperatures range from about 0 C
in winter to about 10 C in summer; mean annual
precipitation is about 1,000 mm in the south, less in
the north.
The principal factors governing the presence
(or absence) of glaciers in Iceland are mean annual
temperature (especially mean summer temperature), mean annual precipitation (especially mean
winter precipitation), and topographic elevation.
These factors, in turn, govern the glaciation limit
(Neuendorf et al. 2005, p. 273) throughout Iceland:
the lowest occurs at about 700 m in the Vestfirdir
(Northwest Fjords), and the highest north of
Special topics and methodology
Vatnajökull at more than 1,500 m. On the southern
flanks of Vatnajökull, Mýrdalsjökull, and Eyjafjallajökull, where the highest mean annual precipitation occurs, the glaciation limit is about 1,100 m
(Thorarinsson 1975).
The climate in Iceland was colder during the
Little Ice Age, and outlet glaciers and mountain
glaciers expanded to their maximum extent at the
end of the cold period, about 1890. During the 20th
century, Iceland’s glaciers retreated to positions
equivalent to their probable locations of about
four centuries earlier. The 1940s, in particular, were
characterized by rapid retreat of glacier termini and
thinning. However, during intervals in the 1970s
and 1980s, extending into the early 1990s, the
majority of Iceland’s glaciers thickened and
advanced. Since the mid-1990s, most of Iceland’s
glaciers have retreated and thinned very rapidly in
response to warmer summers (Sigurdsson 2005).
Fig. 18.3 shows the close correlation of annual
415
fluctuations of the terminus of the Sólheimajökull
outlet glacier in southern Iceland and Hyrningsjökull outlet glacier in western Iceland with variations in mean annual summer temperature at
Stykkishólmur, where a coastal meteorological
station in western Iceland recorded data during
the period 1930 to 2010.
18.3
SPECIAL TOPICS AND
METHODOLOGY
18.3.1 Types of glaciers
In general, glaciers are of two types with regard to
the reaction of the terminus to variations in mass
balance:
. nonsurge type
. surge type.
Figure 18.3. Graph showing annual variations in the terminus of Sólheimajökull, an outlet glacier from the
Mýrdalsjökull ice cap, southern Iceland, and Hyrningsjökull outlet glacier from the Snæfellsjökull ice cap, western
Iceland, correlated with mean summer temperature (May–September) at the Stykkishólmur meteorological station,
western Iceland: 1930–2010 (updated from Sigurdsson 2006).
416
Remote sensing of mountain glaciers and ice caps in Iceland
The terminus of a surge-type glacier ordinarily
retreats most of the time regardless of climate and
mass balance and advances only occasionally at a
quasiregular interval of time (usually of the order of
decades) (Björnsson et al. 2003). The terminus of a
nonsurge-type glacier in Iceland will react more or
less directly to changes in mass which, in turn,
depends primarily on radiation and mean summer
temperature (Fig. 18.3). Occasional anomalies in
precipitation also appear in glacier oscillations such
as the retreat of glacier termini during the cold and
dry period in the 1960s (Crochet 2007, Sigurdsson
et al. 2007, their fig. 6).
The climate-induced oscillations in mass balance
of glaciers in Iceland is primarily based on two
factors:
. radiation and air temperature during the summer
. precipitation during the winter.
In Iceland, decadal variations of temperature have
been much greater than those of precipitation
(Sigurdsson et al. 2007). Therefore, they are the
most important climatic factors in the variations
of glaciers.
In Iceland several nonclimatic factors also affect
the mass balance of glaciers. The most important of
those are:
. subglacial volcanic activity
. subglacial geothermal activity
. debris on the glacier surface—volcanic airfall
(tephra), landslides, etc.
. iceberg calving into water bodies.
18.3.2 History of Iceland’s
glacier variations
During the Last Glacial Maximum (Weichsel),
Iceland was almost entirely covered by glacier ice.
During the warmest part of the Holocene, about
7800–5600 years bp, glaciers in Iceland more or less
disappeared (Flowers et al. 2008, Geirsdóttir et al
2009), leaving only the highest mountains with ice
caps. The maximum glacier extent of postglacial
time in Iceland occurred around 1890 (Sigurdsson
2005). Therefore, glaciers have, by their advance,
obliterated a substantial portion of the evidence of
fluctuations prior to 1890 and we have to rely on
scarce stratigraphical information and other geological evidence. Patches of peat, tree stumps, and
lumps of diatomite with intact stratigraphy in the
outwash from major outlet glaciers confirm in rather
inexact terms a much greater extent presently than
during the middle of the Holocene.
At the time of settlement about 900 ad, the presence of glaciers and the turbid water of the glacial
rivers were noted and recorded in early manuscripts
such as The Book of Settlement (Benediktsson
1986). The same source gives ample place names
that include glaciers in their names. This confirms
that the major glaciers were present during that
time; however, they were much smaller than during
the 20th century.
According to historical documents, glaciers
advanced with minor retreat events more or less
continuously at least since the 17th century, until
the end of the 19th century. Grazing areas, forests,
and inhabited districts were overrun by glaciers,
indicating that this was the greatest advance of
glaciers since the last glaciation (Sigurdsson 2005).
During the Little Ice Age Icelandic glaciers
reached their maximum extent about 1890. The
retreat of glaciers, however slow, was obvious
during the first decades of the 20th century (Björnsson 1988). In the 1920s, considerable climate warming resulted in a high rate of retreat of all glaciers in
the country. This retreat continued at a moderate
pace until about 1970. During the period 1970–1995
nonsurge-type glaciers advanced almost continuously due to a cooler climate in an area reaching
from Labrador and across southern Greenland to
Iceland (Hanna et al. 2004). During the first decade
of the 21st century glaciers have retreated faster
than at any time since 1930, when the Iceland
Glaciological Society began monitoring glacier
front variations (Figs. 18.1 and 18.3) (Jóhannesson
and Sigurdsson 1998, Sigurdsson 1998, 2006).
During the past decade, glacier surface area has
decreased on average by about 0.3% per year, as
deduced from repeated tracing of outlines of
glaciers from map overlays of Landsat 7, SPOT5, vertical aerial photos, with complementary data
from oblique aerial stereo photographs and ground
verification for some glaciers, and by about 0.4% in
thickness according to mass balance measurements
(Sigurdsson 2006). According to models of mass
balance, Icelandic glaciers will essentially disappear
during the next two centuries if global warming
continues as expected (Jóhannesson et al. 2007).
Outlines of all Icelandic glaciers have been traced
recently on map overlays from aerial photos, Landsat 7, and SPOT-5 images (Sigurdsson and Williams
2008b), and interpretation of the location of the
outlines has been verified by oblique aerial stereo
Special topics and methodology
photographs and ground measurements at the end
of a warm summer.
Nonsurge-type glaciers in Iceland usually do
react to mass balance changes almost immediately
(Sigurdsson et al. 2007) (Fig. 18.3). Best fit
(r 2 ¼ 0.716) between the 5-year running mean of
front variations of Sólheimajökull outlet glacier,
southern Iceland and summer temperature at Stykkishólmur in western Iceland is attained if glacier
reaction to mass balance change has a 1-year time
lag. Similar values occur for other nonsurge-type
glaciers independent of their size.
During the 20th century glaciers in Iceland
retreated approximately as far as they had
advanced from 1600 to 1900 (Sigurdsson 2005).
Glaciers decrease in proportion to their size. The
largest glaciers have retreated about 4–5 km but the
small mountain glaciers of northern Iceland have
retreated only of the order of 100 m. Cirque glaciers
that are covered by debris in the ablation area have
decreased very little in length. A few of the smallest
glaciers have disappeared, leaving only remnants
such as ice-cored moraines.
18.3.3 Identifying the outline, transient
snow line, and firn line of glaciers
The main problems in identifying the glacier margin
by remote sensing in Iceland are mainly debris
cover on outlet glaciers and snow cover at high
elevations. Many small mountain glaciers may be
completely covered with snow for extended periods,
some for decades.
Glaciers may become covered by surficial debris
by several means. In steep-sided landscape landslides or rockslides frequently fall on the glaciers’
surfaces (Sigurdsson and Williams 1991). These can
usually be identified in early stages on satellite
images. Later the landslides merge with debris at
the terminus and are then difficult to distinguish
from the morainal and fluvioglacial deposits in
the outwash plain. Cirque glaciers commonly accumulate debris in the ablation area; such surficial
debris may cover more than half of the surface area
of the glacier. This debris results from rock fall at
the head wall and is not easy to identify on satellite
images or discern between the proglacial area and
ice-cored moraines. Field observations are needed
to accurately map the position of the glacier terminus. When ground observations are not feasible
oblique aerial photography, particularly in stereo,
will suffice generally.
417
Glaciers in Iceland commonly are covered by
deposits of tephra downwind from sites of recent
explosive volcanic eruptions. In the ablation area
this will wash off with meltwater or rain; in the
accumulation area it will be covered with subsequent snow. However, outlet glaciers, such as
Kötlujökull, Skeidarárjökull, and Dyngjujökull,
that originate near the most active volcanoes generate quite voluminous layers of tephra that melt
out of the glacier ice in the ablation area. This is a
very efficient insulation material that affects mass
balance and, thereby, variations at the terminus.
Satellite images commonly reveal the transient
snow line (Jaenicke et al. 2006), which delineates
the approximate position of the equilibrium line
at the end of the ablation season. The firn line is
also often easily detectable in late summer. Because
of the presence of tephra layers in Icelandic glaciers
the difference between the transient snow line and
the firn line is, in many instances, obvious on satellite images. The firn line defines the long-term equilibrium line altitude (ELA), thereby allowing for
determination of the accumulation area ratio
(AAR). The AAR is close to constant for different
ice flow basins and, therefore, the firn line is very
helpful in accurate identification of ice divides on
ice caps.
Calving of glaciers into the sea or lakes affects
their overall mass balance to a great extent because
the masses of glacier ice that melt (e.g., icebergs)
beyond the margin of the glacier are not included in
the ablation caused by climatic change. Lakes at the
glacier margin are easily identified and the increased
velocity resulting from the calving process is commonly visible by the pattern of tephra layers even on
satellite images (e.g., Breidamerkurjökull; Williams
and Sigurdsson 2004, their fig. 18.3).
18.3.4 Jökulhlaups
Ice-dammed lakes are common in Iceland. Periodically, these ice dams fail, either suddenly or with a
gradual exponential increase in discharge. In either
case, the result is a dramatic release of water from
behind the dam. As noted, the phenomenon was
first described scientifically by Thorarinsson
(1939) with regard to two types of glacier outburst
floods. He used the term jökulhlaup for both; it has
since been adopted into the international terminology of glaciology and by other geoscientists
(Neuendorf et al. 2005, p. 345).
Most ice-dammed lakes are in tributary valleys
(Thorarinsson 1939). A few are subglacial, formed
418
Remote sensing of mountain glaciers and ice caps in Iceland
by subglacial geothermal areas that continuously
melt the glacier from below. This causes a subsidence in the surface of the glacier, creating a
cauldron bounded by concentric fractures that, in
turn, forms a trap collecting subglacial water and
forming a cupola at the glacier bed (Björnsson
1988). The burst of water from this cupola in a
jökulhlaup accentuates the existing cauldron on
the glacier surface which gradually is lifted from
below by water from surficial, englacial, and subglacial meltwater and geothermally melted glacier
ice and filled from the top by accumulating snow
until the next jökulhlaup occurs. These cauldrons
are easily detected on satellite images, forming concentric fissures that outline the depression on the
surface of the glacier. The extent of inundation by
floods is only in exceptional cases caught by remote
sensing.
The impact of jökulhlaups on the topography
may be huge. Large canyons may be cut into the
landscape in a very short period of time; outwash
plains of large or repeated jökulhlaups are easily
discerned on satellite images. The largest of those
in Iceland is the Skeidarársandur outwash plain
which covers an area of about 1,000 km 2 . During
a recent jökulhlaup (November 1996) 750 km 2 of
the outwash plain was inundated (Snorrason et al.
2002). The hazard represented by jökulhlaups for
Icelandic society is very great. On average, there are
about 5–10 jökulhlaups per year in Iceland
(Sigurdsson and Einarsson 2005). Usually, there is
at least one per century that exceeds 100,000 m 3 s1
and 5–10 per century that are tens of thousands of
m 3 s 1 . These will inevitably cause damage to infrastructure, such as the roads and bridges that traverse glacial outwash plains. The most catastrophic
jökulhlaups are induced by subglacial volcanic
eruptions. The jökulhlaup associated with the
1996 Gjálp eruption within Vatnajökull is described
below.
18.4
THREE CASE STUDIES
18.4.1 Transient tephra lines
On average, a volcanic eruption occurs every 3–4
years in Iceland (Gudmundsson et al. 2008).
Volcanic tephra is frequently deposited on glacier
surfaces within the country. These layers of tephra
appear in the ablation area as dark undulating
bands often easily identifiable on satellite images
and aerial photos (Larsen et al. 1998). Melting of the
glacier surface will displace the outcrops of tephra
layers (horizons) upglacier because they are dipping
at a slight angle into the ice. However, these bands
move gradually toward the terminus because of the
movement of the glacier and eventually merge with
other debris at the margin of the glacier. By identifying individual tephra layers and determining their
age, the turnover time of each outlet glacier can be
calculated (Sigurdsson 2010).
The forward motion of surge-type glaciers is
episodic with great leaps forward during surges,
but becoming more or less stagnant during periods
of quiescence. By tracing identified tephra layers on
images at two or more different times, glaciers with
normal downglacier movement (equilibrium velocity) can be distinguished. Stagnant ice masses can be
identified by displacement of tephra horizons upglacier indicating a surge-type glacier (e.g., Brúarjökull) (Fig. 18.4).
Tephra horizons keep their stratigraphic position
all the way down to the terminus. This indicates
that the flow within the glacier mass is more or less
perfectly laminar even where the thickness of the
glacier is halved and doubled again by flowing
across subglacial serrated volcanic mountain ridges
(e.g., Tungnárjökull).
18.4.2 Classification of the Vatnajökull
ice cap according to three
different outlines
Tracing the outline of an ice cap or two or more
different glaciers within the same region at two or
more different times will generally indicate which
glaciers or which outlet glaciers from the ice cap are
showing a surge-type and tidewater (‘‘abnormal’’)
or nonsurge-type (‘‘normal’’) flow process. During
a period of positive mass balance, surge-type
glaciers retreat except during surge events, whereas
nonsurge-type glaciers advance. During the quiescence phase surge-type glaciers retreat at a higher
rate than nonsurge-type glaciers during a time of
negative mass balance. For two different map
outlines of surge-type and nonsurge-type glaciers,
glaciers that have surged in the interval of time
between outlines are easily identified.
In Fig. 18.5, three different outlines of Vatnajökull ice cap are shown. The partial 1903–1904
outline of southeastern and southern Vatnajökull
is traced from the Danish General Staff map, scale
1:50,000; the 1945–1946 outline (complete) is traced
Three case studies
419
Figure 18.4. Brúarjökull outlet glacier with distinct tephra horizons. One of them, tephra from the Grı́msvötn
eruption in 1629, is traced at two different times: 2000 (yellow), and 2006 (red) projected on IRS satellite image.
Figure can also be viewed in higher resolution as Online Supplement 18.1.
from Army Map Service maps, Series 762, scale
1:50,000 published in 1950. The outline from 1991
to 1992 is traced on a map overlay from Landsat 5
satellite images taken on September 7, 1991 (middle
and eastern part of the ice cap) and July 14, 1992
(the westernmost outline). The ice cap is successively smaller in the three cases. However, some
outlet glaciers extend farther out as plotted on more
recent maps or traced on overlays of satellite images
than from earlier datasets; these are all surge-type
glaciers, such as Brúarjökull on the northeast
margin and Sı́dujökull on the southwest margin.
In other cases the respective distance between successive outlines is much greater for some glaciers
than others. This may be explained by variable rates
of calving glaciers (tidewater glaciers, such as
Breidamerkurjökull) or surge-type glaciers during
quiescence phases (Tungnárjökull between the first
two outlines). Between 1945 and 2006 all but one of
the recognized surge-type outlet glaciers of Vatnajökull ice cap underwent a surge event.
18.4.3
The impact of the 2004 jökulhlaup
on glacier dynamics of
Skeidarárjökull
In this study the influences of the 2004 jökulhlaup
on the ice dynamics of Skeidarárjökull are investigated by means of optical imagery acquired by the
Advanced Spaceborne Thermal Emission and
Reflection Radiometer (ASTER) aboard the EOS
Terra satellite. Skeidarárjökull is the largest southward-trending outlet of the Vatnajökull ice cap with
a catchment area of approximately 1,450 km 2 . Its
elevation ranges from 1,740 m down to 100 m asl
at the terminus. Jökulhlaup draining under
Skeidarárjökull in autumn 2004 was associated with
a volcanic eruption at the subglacial Grı́msvötn
caldera (November 1–6, 2004) (Martinis et al.
2007). The meltwater discharge of this outburst
flood peaked on November 2 and finally ended in
early December, having released a total volume of
0.8 km 3 from Grı́msvötn.
420
Remote sensing of mountain glaciers and ice caps in Iceland
Figure 18.5. Vatnajökull ice cap with three different outlines: 1903–1904 (partial), 1945–1946 (complete), and
1991–1992 (complete).
Six optical ASTER scenes (band 1, 0.52–0.60 mm)
covering the time period 2001–2005 are used to
compare short-term (September 27, 2004 to
November 30, 2004) variation in surface velocity
related to the jökulhlaup using mean annual
velocities. Surface velocities and the flow pattern
of the glacier tongue are derived by image-to-image
cross-correlation determined using IMCORR software (Scambos et al. 1992) applied to five ASTER
image pairs. This technique automatically tracks
the motion of small-scale features like crevasses,
debris, dirt cones, or other objects at the glacier
surface. Generally, the four annual ASTER pairs
(2001–2002, 2002–2003, 2003–2004, 2004–2005)
offer a higher density of correlated points, due to
the similar surface conditions during the summer
period when the ice is exposed on the whole glacier
tongue (see the mean annual flow pattern of the
time interval September 27, 2004 to July 28, 2005
in Fig. 18.6a). Therefore, surface features are well
correlated. Cross-correlation of the annual pairs
yields very similar flow patterns with a pronounced
north-northeast to south-southwest trending cen-
tral flow line of maximum speed (up to 1.05 m
day1 ) in contrast to the lateral parts of slower
movement (<0.1 m day1 ). Feature tracking of
the data pair covering the jökulhlaup (September
27, 2004 to November 30, 2004) was complicated by
snow cover in the ASTER scene acquired on
November 30, 2004, especially at higher elevations
of Skeidarárjökull. Nevertheless, correlation point
density is reduced only marginally in the lower parts
of the glacier on this date (Fig. 18.6b), because
surface features are not completely masked by the
thin snow cover. A considerable increase in flow
velocity of up to 0.4 m day1 compared with annual
values can be observed, probably due to enhanced
glacier sliding triggered by the higher amount of
subglacial meltwater drainage during the jökulhlaup, caused by the Grı́msvötn volcanic eruption
(Münzer et al. 2007). Extensive acceleration over
nearly the whole width of the glacier suggests widespread lubrication at the glacier bed. This phenomenon is hardly explainable by the classical
jökulhlaup theory of floodwater drainage in a single
subglacial conduit (Nye 1976); a sheet flow or
Regional summary
421
Figure 18.6. Surface velocity field of Skeidarárjökull outlet glacier, derived from ASTER data for the periods (a)
September 27, 2004 to July 28, 2005, (b) September 27, 2004 to November 30, 2004 (Martinis et al., 2007).
coupled sheet and tunnel seems more likely (Jóhannesson 2002; Flowers et al. 2004). This corresponds
to the new theory of meltwater discharge during
glacial torrents already confirmed for a major
jökulhlaup at Skeidarárjökull in 1996 (Magnússon
et al. 2005).
18.5
REGIONAL SUMMARY
In 2000, 10.7% (11,079 km 2 ) of the land area of
Iceland (103,000 km 2 ) was covered by glaciers
(Table 18.1). Iceland’s glaciers can be placed within
eight regional glacier groups (Fig. 18.2). Most of the
area, 10,718 km 2 (97%) of glacier ice, is contained
in the six largest ice caps and associated outlet
glaciers in five of the groups (Table 18.1): Vatnajökull (73%), Langjökull (8.3%), Hofsjökull (8%),
Mýrdalsjökull (5.4%), Drangajökull (1.3%), and
Eyjafjallajökull (less than 1%). All six ice caps have
annual precipitation in excess of 2,500 mm; Langjökull receives more than 3,500 mm; and Mýrdals-
jökull, Eyjafjallajökull, and Vatnajökull exceed
4,000–5,000 mm, peaking at 7,000 mm. Hofsjökull
and Drangajökull receive about 3,500 mm of precipitation annually (Björnsson and Pálsson 2008,
Sigurdsson et al. 2004).
According to Sigurdsson and Williams (2008a),
the 269 named glaciers in Iceland include 14 ice caps
(including 2 contiguous ice caps), 109 outlet glaciers
(from the ice caps), 8 ice flow basins in the
Hofsjökull ice cap, and 3 ice streams (in
Breidamerkurjökull). There are also 55 cirque
glaciers, 73 mountain glaciers, and 5 valley glaciers,
most of which are in the Tröllaskagi and other
highlands of northern Iceland. There are 21
surge-type glaciers (Björnsson et al. 2003), not
counting 7 candidates. There are 38 named snow
patches. The total number of named glaciers do not
include the 6 glaciers that ‘‘disappeared’’ during the
second half of the 20th century: 3 mountain glaciers
which melted, 2 distributary outlet glaciers, and 1
outlet glacier that receded into their respective ice
caps.
422
Remote sensing of mountain glaciers and ice caps in Iceland
The primary glaciological hazard is the jökulhlaup. Jökulhlaups are of two types, those that
result from subglacial volcanic and associated
geothermal activity and those that result from the
failure of ice-dammed ice-marginal lakes (proglacial
lakes). Other glaciological hazards include surgetype glaciers, snow avalanches, and flooding from
ice dams on rivers.
Since 1930 an increasing number of glacier termini have been measured annually in the field; in
2009 between 40 and 50 glacier termini (mostly outlet glaciers) at 55 separate locations were being
measured. Accurate mapping of Iceland began in
1902, and several series of maps at various scales
have been published of Iceland’s glaciers. Radioecho sounding of the thickness of Iceland’s ice caps
was begun in 1976 (Björnsson 1978b, 1988). Geodetic airborne laser altimetry or LiDAR (Jóhannesson et al. 2013) and airborne thermal infrared
imagery has been analyzed for Icelandic glaciers.
Image and nonimage data acquired by sensors on
polar-orbiting satellites, including MSS, RBV, TM,
ETMþ, and OLI imaging sensors on the Landsat
series (1972–present), SPOT (Berthier et al. 2006),
radar images from sensors on Seasat and InSAR
images from ERS-1 (Magnússon et al. 2005),
images from ASTER on Terra (Martinis et al.
2007), and surface elevation profiles from GLAS
data on ICESat, etc., have been analyzed to provide
information on fluctuations of termini, changes
in area, and other glaciological parameters of
Iceland’s glaciers.
Long-term datasets include quantitative measurements of the weather and climate of Iceland
(since the late 19th century); repetitive mapping
of Iceland’s glaciers (begun in southeast Iceland
in 1903); field measurements of fluctuations of
glacier termini (begun in 1930); determination of
the thickness of Iceland’s ice caps by radio-echo
sounding (begun in 1976); repetitive acquisition of
aerial photographs (begun in the 1930s); acquisition
of airborne thermal infrared imagery (1969); geodetic airborne laser altimetry surveys (1993) and in
2008–2013; and repetitive acquisition of satellite
images (begun in 1972); as well as other sensor data
from polar-orbiting satellites. All these datasets
provide glaciologists with the opportunity to monitor changes in Iceland’s glaciers over time and to
correlate changes in climate in Iceland with fluctuations of termini, area, and volume of Iceland’s glaciers during the past 80 years (since 1930), for more
than 100 years in the case of the earliest modern
maps (since 1903 for outlet glaciers of Vatnajökull
in southeastern Iceland) (Jóhannesson et al., 1995;
Sigurdsson and Jónsson, 1995; Jóhannesson, 1997;
Jóhannesson and Sigurdsson, 1998). Many of the
datasets are updated annually, so the correlation of
climate change with fluctuations of Iceland’s glaciers will continue during the 21st century and
beyond.
Since the turn of the century, the glaciers of Iceland are shrinking in area at an average rate of
0.3% a year. If the shrinkage in area (and volume)
of Iceland’s glaciers continues at the same rate,
Iceland is likely to become nearly completely deglacierized (except at the highest elevations) by
2200 (Jóhannesson et al. 2007).
18.6
ACKNOWLEDGMENTS
ASTER data courtesy of NASA/GSFC/METI/
Japan Space Systems, the U.S./Japan ASTER
Science Team, and the GLIMS project.
18.7
REFERENCES
Benediktsson, J. (Ed.) (1986) I´slendingabók og Landnámabók (Book of Icelanders and the Book of Settlement), Fornritafélagid, Reykjavı́k, 525 pp. þ maps [in
Icelandic].
Berthier, E., Björnsson, H., Pálsson, F., Feigl, K.L.,
Llubes, M., and Rémy, F. (2006) The level of Grı́msvötn subglacial lake, Vatnajökull, Iceland, monitored
with SPOT 5 images. Earth and Planetary Science Letters, 243(1/2), 293–302.
Björnsson, H. (1978a) The surface area of glaciers in
Iceland. Jökull, 28, 31.
Björnsson, H. (1978b) Könnun á jöklum med rafsegulbylgjum (Radio-echosounding of temperate glaciers).
NáttúrufræBingurinn, 47(3/4), 184–194 [in Icelandic].
Björnsson, H. (1979) Glaciers in Iceland. Jökull, 29, 74–
80.
Björnsson, H. (1988) Hydrology of Icelandic ice caps in
volcanic regions. Vı´sindafe´lag I´slendinga (Societas
Scientiarum Islandica), 45, 139.
Björnsson, H. (2009) Jöklar á I´slandi (Glaciers in
Iceland), Bókaútgáfan Opna, Reykjavı́k, 479 pp. [in
Icelandic].
Björnsson, H., and Pálsson, F. (2008) Icelandic glaciers.
Jökull, 58, 365–386.
Björnsson, H., Pálsson, F., Sigurdsson, O., and Flowers,
G.E. (2003) Surges of glaciers in Iceland. Annals of
Glaciology, 36, 82–90.
Bödvarsson, Á. (1996) Landmælingar og KortagerM Dana
á I´slandi, Upphaf Landmælinga Íslands, Reykjavı́k,
316 pp. [in Icelandic].
References 423
Crochet, P. (2007) A Study of Regional Precipitation
Trends in Iceland Using a High-Quality Gauge Network
and ERA-40 (AMS Monogr. Vol. 28, Issue 50), American Meteorological Society, Boston, doi: 10.1175/
JCLI4255.1, pp. 4659–4677.
deBlij, H.J., Muller, P.O., and Williams, R.S., Jr. (2004)
Physical Geography: The Global Environment, Oxford
University Press, New York, 702 pp.
Einarsson, M.Á. (1976) VeMurfar á I´slandi (Climate of
Iceland), Idunn, Reykjavı́k, 150 pp. [in Icelandic].
Einarsson, M. (1984) Climate of Iceland. In: H. van Loon
(Ed.), World Survey of Climatology: Climate of the
Oceans, Vol. 15, pp. 673–697.
Eythorsson, J. (1963) Variation of Iceland’s glaciers
1931–1960. Jökull, 13, 31–33.
Eythorsson, J., and Sigtryggsson, H. (1971) The climate
and weather of Iceland, The Zoology of Iceland, Vol. I,
Part 3, Ejnar Munksgaard, Copenhagen, 62 pp.
Eythorsson, J., Rist, S., and Sigurdsson, O. (1951–) Jöklabreytingar. Jökull, 1– (Annual reports of glacier variations: 1951–1966, 1–16 by J. Eythorsson; 1967–1986,
17–37 by S. Rist; and 1987–2007, 38–57, continuing by
O. Sigurdsson).
Flowers, G., Björnsson, H., Pálsson, F., and Clarke, G.
(2004) A coupled sheet-conduit mechanism for jökulhlaup propagation. Geophysical Research Letters,
31(5), doi: 10.1029/2003GL019088.
Flowers, G.E., Björnsson, H., Geirsdóttir, Á., Miller,
G.H., Black, J.L., and Clarke, G.K.C. (2008) Holocene
climate conditions and glacier variation in central Iceland from physical modelling and empirical evidence.
Quaternary Science Reviews, 27, 797–813.
Friedman, J.D., Williams, R.S., Jr., Pálmason, G., and
Miller, C.D. (1969) Infrared surveys in Iceland in 1966.
Geological Survey Research 1969 (USGS Professional
Paper 650-C), U.S. Geological Survey, Reston, VA,
pp. C89–C105.
Friedman, J.D., Williams, R.S., Jr., Thorarinsson, S., and
Pálmason, G. (1972) Infrared emission from Kverkfjöll
subglacial volcanic and geothermal area, Iceland.
Jökull, 22, 27–43.
Garvin, J.B., and Williams, R.S., Jr. (1993) Geodetic airborne laser altimetry of Breidamerkurjökull and
Skeidarárjökull, Iceland, and Jakobshavn Isbræ, West
Greenland. Annals of Glaciology, 17, 379–385.
Geirsdóttir, Á., Miller, G.H., Axford, Y., and Ólafsdóttir, S. (2009) Holocene and latest Pleistocene
climate and glacier fluctuations in Iceland. Quaternary
Science Reviews, 28, 2107–2118.
Grove, J.M. (1988) The Little Ice Age, Routledge, New
York, 498 pp.
Gudmundsson, M.T., Larsen, G., Höskuldsson, Á., and
Gylfason, Á.G. (2008) Volcanic hazards in Iceland.
Jökull, 58, 251–268.
Gunnlaugsson, B. (1848) Uppdráttr I´slands, Hid ı́slenska
bókmenntafélag, Reykjavı́k (4 map sheets at scales of
1:480,000) [in Icelandic].
Hall, D.K., Williams, R.S., Jr., and Sigurdsson, O. (1995)
Glaciological observations on Brúarjökull, Iceland,
using Landsat TM and ERS-1 SAR data. Annals of
Glaciology, 21, 271–276.
Hanna, E., Jónsson, T., and Box, J.E. (2004) An analysis
of Icelandic climate since the nineteenth century. International Journal of Climatology, 24, 1193–2004.
Jaenicke, J., Mayer, C., Scharrer, K., Münzer, U., and
Gudmundsson, Á. (2006) The use of remote sensing
data for mass-balance studies at Mýrdalsjökull ice cap,
Iceland. Journal of Glaciology, 52(179), 565–573.
Jóhannesson, T. (1997) The response of two Icelandic
glaciers to climatic warming computed with a degreeday glacier mass balance model coupled to a dynamic
glacier model. Journal of Glaciology, 43(143), 321–327.
Jóhannesson, T. (2002) Propagation of a subglacial flood
wave during the initiation of a jökulhlaup. Hydrological Sciences Journal, 47(3), 417–434.
Jóhannesson, T., and Sigurdsson, O. (1998) Interpretation of glacier variations in Iceland 1930–1995. Jökull,
45, 27–33.
Jóhannesson, T., Sigurdsson, O., Laumann, T., and
Kennett, M. (1995) Degree-day mass balance modelling with applications to glaciers in Iceland, Norway
and Greenland. Journal of Glaciology, 41(138), 345–
358.
Jóhannesson, T., Adalgeirsdóttir, G., Björnsson, H.,
Crochet, P. Elı́asson, E.B., Gudmundsson, S., Jónsdóttir, J.F., Ólafsson, H., Pálsson, F., Rögnvaldsson,
Ó. et al. (2007) Effect of Climate Change on Hydrology
and Hydro-resources in Iceland (OS-2007/011),
National Energy Authority, Reykjavı́k, 91 pp.
Larsen, G., Gudmundsson, M.T., and Björnsson, H.
(1998) Eight centuries of periodic volcanism at the
center of the Iceland hotspot revealed by glacier
tephrostratigraphy. Geology, 26(10), 943–946.
Magnússon, E., Rott, H., Björnsson, H., Roberts, M.J.,
Berthier, E., and Pálsson, F. (2005) The effects of basal
water beneath Vatnajökull, Iceland, observed by SAR
interferometry. Proceedings of FRINGE, 2005,
Frascati, Italy.
Magnússon, E., Björnsson, H., Rott, H., Roberts, M.J.,
Pálsson, F., Gudmundsson, S., Bennett, R.A., Geirsson, H., and Sturkell, E. (2011) Localized uplift of
Vatnajökull, Iceland: Subglacial water accumulation
deduced from InSAR and GPS observations. Journal
of Glaciology, 57(203), 475–484.
Martinis, S., Scharrer, K., Münzer, U., Mayer, C., and
Gudmundsson, Á. (2007) Influence of the 2004 jökulhlaup on ice dynamics of Skeidarárjökull, Iceland,
using Terra-ASTER imagery. Photogrammetrie, Fernerkundung, Geoinformation, 5, 337–347.
Münzer, U., Scharrer, K., Gudmundsson, A., and Martinis, S. (2007) NRT monitoring of the 2004 subglacial
Grı́msvötn eruption (Iceland) with ENVISAT-ASAR
data. ENVISAT Symposium, April 2007, Montreux
(ESA SP 636), ESA, Noordwijk, The Netherlands.
424
Remote sensing of mountain glaciers and ice caps in Iceland
Neuendorf, K.K.E., Mehl, J.P., Jr., and Jackson, J.A.
(Eds.) (2005) Glossary of Geology (Fifth Edition),
American Geological Institute, Alexandria, VA,
779 pp.
Nørlund, N.E. (1944) Islands Kortlægning: En historisk
Fremstilling (Geodætisk Instituts Publikationer No.
7), E. Munksgaard, København, 110 pp. [in Danish].
Nye, J. (1976) Water flow in glaciers: jökulhlaups, tunnels
and veins. Journal of Glaciology, 17, 181–207.
Ólafsson, H., Furger, M., and Brümmer, B. (2007) The
weather and climate of Iceland. Meteorologische Zeitschrift, 16(1), 5–8.
Rist, S. (1976) Jöklabreytingar 1931/64, 1964/74 og 1974/
75: Athugasemdir og vidaukar. Jökull, 25, 77 [in Icelandic].
Rist, S. (1985) Glaciers in Iceland: Division into Regional
Groups and Suggested Classification in Coastal and
Inland Glaciers within Each Group, Orkustofnun, Vatnamælingar, Reykjavı́k, 6 pp. (unpublished; 4 page
manuscript of the eight glacier groups divided as
coastal and inland, with a list of glacier place names
and names of snow patches; and a map, VOD VM 925
S Rist 85 07 0940 IS, entitled ‘‘Glaciers and the main
snow patches in Iceland’’—see appendix in Sigurdsson
and Williams, 2008a).
Sæmundsson, K. (1980) Outline of the geology of Iceland.
Jökull, 29, 7–28.
Scambos, T.A, Dutkiewicz, M.J., Wilson, J.C., and
Bindschadler, R.A. (1992) Application of image
cross-correlation to the measurements of glacier velocity using satellite image data. Remote Sensing of Environment, 42(3), 177–186.
Shuman, C.A., Sigurdsson, O., Jónsdóttir, J.F., Williams,
R.S., Jr., and Hall, D.K. (2008) Comparison of the
topography of Drangajökull ice cap, Iceland, cloudcleared ICESat profiles and GPS ground-survey and
GIS data (abstract). International Workshop on Mass
Balance Measurements and Modelling, March 26–28,
2008, Skeikampen, Norway, International Glaciological Society, Cambridge, U.K.
Sigurdsson, H. (1978) Kortasaga I´slands frá lokum 16.
aldar til 1848, Bókaútgáfa Menningarsjóds og
Rjódvinafélagsins, Reykjavı́k, 279 pp. [in Icelandic].
Sigurdsson, O. (1998) Glacier variations in Iceland 1930–
1995: From the database of the Iceland Glaciological
Society. Jökull, 45, 1–25.
Sigurdsson, O. (2005) Variations of termini of glaciers in
Iceland in recent centuries and their connection with
climate. In: C. Caseldine, A. Russell, J. Hardardóttir,
and Ó. Knudsen (Eds.), Iceland: Modern Processes and
Past Environments, Elsevier, London, pp. 241–408.
Sigurdsson, O. (2006) Jöklabreytingar 1930–1970, 1970–
1995, 1995–2004 og 2004–2005 (Glacier variations
1930–1970, 1970–1995, 1995–2004 and 2004–2005).
Jökull, 56, 85–91 [in Icelandic].
Sigurdsson, O. (2010) Variations of Mýrdalsjökull during
postglacial and historical times. In: A. Schomacker,
J. Krüger, and K.H. Kjær (Eds.), The Mýrdalsjökull
Ice Cap, Iceland: Glacial Processes, Sediments and
Landforms on an Active Volcano (Developments in
Quaternary Science No. 13), Elsevier, Amsterdam,
pp. 69–78.
Sigurdsson, O., and Einarsson, B. (2005) Jökulhlaupaannáll 1989–2004 (Annals of Jökulhlaups 1989–2004)
(Rep. OS-2005/031), National Energy Authority,
Reykjavı́k, 46 pp. [in Icelandic].
Sigurdsson, O., and Jónsson, T. (1995) Relation of glacier
variations to climate changes in Iceland. Annals of
Glaciology, 21, 263–270.
Sigurdsson, O., and Williams, R.S., Jr. (1991) Rockslides
on the terminus of ‘‘Jökulsárgilsjökull,’’ southern
Iceland. Geografiske Annaler, 73A(3/4), 129–140.
Sigurdsson, O., and Williams, R.S., Jr. (2008a) Geographic Names of Iceland’s Glaciers: Historic and Modern (USGS Professional Paper 1746), U.S. Geological
Survey, Reston, VA, 225 pp. Available at http://pubs.
usgs.gov/pp/p1746/
Sigurdsson, O., and Williams, R.S., Jr. (2008b) Assessment of the area of glaciers in Iceland at the beginning
of the 21st century (abstract). International Workshop
on World Glacier Inventory (September 20–24, 2008,
Lanzhou, China), International Glaciological Society,
Cambridge, U.K.
Sigurdsson, O., Thorsteinsson, T., Ágústsson, S.M., and
Einarsson, B. (2004) Afkoma Hofsjökuls 1997–2004
(Mass Balance of Hofsjökull 1997–2004) (Rep. OS2004/029), National Energy Authority, Reykjavı́k, 58
pp. [in Icelandic].
Sigurdsson, O., Jónsson, T., and Jóhannesson, T. (2007)
Relation between glacier-termini variations and summer temperature in Iceland since 1930. Annals of
Glaciology, 46, 170–176.
Snorrason, Á., Jónsson, P., Sigurdsson, O., Pálsson, S.,
Árnason, S., Vı́kingsson, S., and Kaldal, I. (2002)
November 1996 jökulhlaup on Skeidarársandur outwash plain, Iceland. Spec. Publs Int. Ass. Sediment, 32,
55–65.
Thorarinsson, S. (1939) The ice-dammed lakes of Iceland,
with particular reference to their value as indicators of
glacier oscillations. Geografiska Annaler, 21(3/4), 216–
242.
Thorarinsson, S. (1943) Oscillations of the Iceland
glaciers in the last 250 years (Chapter XI in Vatnajökull; Scientific results of the Swedish–Icelandic investigations 1936–37–38). Geografiska Annaler, 25(1/2), 1–
54.
Thorarinsson, S. (1958) Flatarmál nokkura ı́slenzkra
jökla samkvæmt herforingjarádskortunum (Area of
the biggest glaciers in Iceland according to the
Geodætic Institute Maps). Jökull, 8, 25 [in Icelandic].
Thorarinsson, S. (1960) Glaciological knowledge in Iceland before 1800: A historical outline. Jökull, 10, 1–18.
References 425
Thorarinsson, S. (1975) Geology and physical geography.
In: J. Nordal and V. Kristinsson (Eds.), Iceland 874–
1974, Ísafoldarprentsmidja hf., Reykjavı́k, pp. 1–11.
Thorarinsson, S., and Sæmundsson, K. (1980) Volcanic
activity in historical time. Jökull, 29, 29–32.
Thorarinsson, S., Sæmundsson, K., and Williams, R.S.,
Jr. (1974) ERTS-1 image of Vatnajökull: Analysis of
glaciological, structural, and volcanic features. Jökull,
23, 1973, 7–17.
Thoroddsen, R. (1892) Islands Jøkler i Fortid og Nutid.
Geografisk Tidskrift, 11(5/6) (1891-1892), 111–146 [in
Danish].
Thoroddsen, R. (1906) Die Gletscher Islands, Island:
Grundriss der Geographie und Geologie. Petermanns
Geographische Mitteilungen, 152/153, 163–208 [in
German].
Thoroddsen, R. (1911) VII, Jöklar, in Lýsing I´slands,
Band 2: Kaupmannahöfn. Hid ı́slenzka bókmenntafélag, Copenhagen, pp. 1–68 [in Icelandic].
Thoroddsen, R. (1916–17) ÁrferMi á I´slandi ı´ Eúsund ár:
Kaumannahöfn, Hid ı́slenska frædafjelag ı́ Kaupmannahöfn, Copenhagen, 432 pp. [in Icelandic].
USGS (1976) Vatnajökull, Iceland (Fall Scene) (Landsat
Image Format Series, N6359WO1723), U.S. Geological Survey, Reston, VA, scale 1:500,000.
USGS (1977) Vatnajökull, Iceland (Winter Scene) (Landsat Image Format Series, N6359WO1723), U.S. Geological Survey, Reston, VA, scale 1:500,000.
Williams, R.S., Jr. (1983) Satellite glaciology of Iceland.
Jökull, 33, 3–12.
Williams, R.S., Jr. (1986a) Glaciers and glacial landforms. In: N.M. Short and R.W. Blair, Jr. (Eds.),
Geomorphology from Space. A Global Overview of
Regional Landforms (NASA
SP-486), NASA,
Washington, D.C., pp. 521–596. Available at http://
disc.gsfc.nasa.gov/geomorphology/index.shtml
Williams, R.S., Jr. (1986b) Glacier inventories of Iceland:
Evaluation and use of sources of data. Annals of
Glaciology, 8, 184–191.
Williams, R.S., Jr. (1987) Satellite remote sensing of
Vatnajökull, Iceland. Annals of Glaciology, 9, 127–135.
Williams, R.S., Jr., and Sigurdsson, O. (Eds.) (2004)
Draft of a Physical, Geographical, and Historical
Description of Icelandic Ice Mountains on the Basis of
a Journey to the Most Prominent of Them in 1792–1794
(with four plan and eight perspective drawings by S.
Pálsson, 1795), Icelandic Literary Society (Reykjavı́k),
Icelandic Glaciological Society (Reykjavı́k) in cooperation with the International Glaciological Society
(Cambridge, U.K.), 183 pp.
Williams, R.S., Jr., Hall, D.K., and Benson, C.S. (1991)
Analysis of glacier facies using satellite techniques.
Journal of Glaciology, 37(125), 120–128.
Williams, R.S., Jr., Hall, D.K., Sigurdsson, O., and
Chien, J.Y.L. (1997) Comparison of satellite-derived
with ground-based measurements of the fluctuations
of the margins of Vatnajökull, Iceland: 1973–1992.
Annals of Glaciology, 24, 72–80.