Jökull - 01.12.1983, Side 21

Geomorphic Classification of Icelandic Volcanoes
RICHARD S. WILLIAMS, jr.
U. S. Geological Survey, Reston, VA 22092, U. S. A.
SIGURÐUR ÞÓRARINSSON
Science Institute, Univeristy of Iceland, Dunhaga 3, Reykjavík
ELLIOT C. MORRIS
U. S. Geological Survey, Flagstaff AZ 86001, U. S. A.
ABSTRACT
In 1959, Thorarinsson published his first classifcation
of the 13 principal types of Icelandic volcanoes and, in 1968,
published a revision of his earlier one. Both landform
classifcations were based on the relationship of the type of
eruptive products (lava, lava and tephra, ortephra), number
of eruptions (one or more than one), and the form of the
eruptive vent (circularor linear).
In 1980, Thorarinsson, working with Kristján
Saemundsson, made a modification to his previous classifc-
ation schemes. The number of volcanic landforms was reduc-
ed to 11 and limited to subaerial basalt volcanoes. The
number of eruptions necessary to produce a given landform
was eliminated. The stratovolcano (Snaefellsjökull) andthe
stratifed ridge (Hekla) landforms were also eliminated,
because they are central (composite) volcanoes.
Drawing upon this previous work, manyyears of direct
field observation and study (ground and air), and review of
the relevant literature on geomorphology of Icelandic vol-
canoes, a new geomorphic classification of Icelandic vol-
canoes has been developed. The new geomorphic classifc-
ation, which includes all types of Icelandic volcanoes,
distinguishes 27 discrete landforms. It relates the nature of
volcanic activity (effusive, mixed, or explosive); environment
during formation (subaerial, subglacial, or submarine);
andform of feeder conduit (short fissure/tubular conduit or
longfissure) for the three, primary compositional classes of
Icelandic volcanoes: basalt (effusive: lava ring, lava shield,
lava shield row, table mountain, subglacial ridge, seamount,
submarine ridge; mixed: spatter cone, spatter cone row,
scoria cone, scoria cone row, mixed cone row; explosive:
tephra ring, tephra ring row, maar, maar row); rhyolite
(effusive: flow dome); and central (mixed composition of
basic, intermediate, and addic lavas and tephra: composite
cone, composite ridge, composite volcano massij). A
pseudovolcano landform (explosive: pseudocraters) is also
included in the classification.
INTRODUCTION
The volcanoes of Iceland have long held the
interest of Icelandic and non-Icelandic scientists
alike. The geological literature of Iceland is replete
with reference to Iceland’s volcanoes, particularly
its great variety of volcanic landforms. Thorvaldur
Thoroddsen, one of the most prolific scientists ever to
study and publish on various aspects of the geology
and geography of Iceland, was especially interested
in the various shapes of volcanic craters. In 1905,
Thoroddsen published sketch maps of 16 types of
volcanic craters and crater groups. The eminent
German volcanologist, Karl Sapper, in 1908 and
1910, published two papers on volcanic craters and
crater rows. In his classic work on volcanoes, Alfred
Rittman (1962), drawing upon his fieldwork in the
Mývatn area during 1938-39, published sketch
maps of pseudocraters and crater rows. In both his
first edition (1936) and his second edition (1960)
Riltman also published classification schemes for
what he termed „Zentralvulkane" and „Linear-
vulkane.“ By central volcano and linear volcano
Rittman meant an eruption from a central conduit
and a fissure, respectively. Rittman also considered
the quantity of magma erupted and the type of
activity (efiusive, mixed, and explosive) to be im-
portant in the classification of volcanoes.
CLASSIFICATION OF ICELANDIC
VOLCANOES
It wasn’t until the late 1950’s, however, that Sig-
urdur Thorarinsson, drawing upon 25 years of field
observations all over Iceland, a thorough know-
ledge of the geological literature of Iceland, and
familiarity with the Danish geographer Niels Niel-
sen’s classification of volcanoes in general
with specific reference to Iceland (Nielsen
JÖKULL 33. ÁR 19