Jökull - 01.12.1983, Page 23

Fig. 2. Oblique aerial photo-
graph of one of the 21 basalt
volcano landforms, of the
Lava Ring, Eldborg, in
Hnappadalssýsla, about 75
km NNW of Reykjavík.
Photo No. H-15 taken on 21
July 1979 by Richard S. Wil-
liams, Jr. View looking E.
(circular or linear). Aside from changing the type
locality of one of the lava landforms (for example,
Threngslaborgir instead of Svörtuborgir, because
the latter is not shown on generally available maps
of the area), and eliminating the lava fissure (for
example, Ogmundargjá), the two landform
classifications were quite similar. By 1968, however,
Thorarinsson had settled on 12 basic landform types
and had restricted his classification to Icelandic
types of basalt volcanoes.
In 1980, Thorarinsson, working with Kristján
Saemundsson, made a modification to the initial
classification, restricted the classification to types of
subaerial basalt volcanoes in Iceland, and reduced
the number of landforms to 11. The lava landforms
were reduced from 3 to 2 by transferring the lava
crater (cone) row landform from the lava to the lava
and tephra category, and two difierent types of
crater row types were placed in the lava and tephra
category. In the 1980 classification the number of
eruptions necessary to produce a given landform
was eliminated (no longer considered to be a
diagnostic characteristic). The stratified (com-
posite) cone or stratovolcano (Snaefellsjökull) and
the stratified (composite) ridge (Hekla) landforms
were also eliminated from the 1980 classification
scheme, because they are now classified as central
volcanoes, being composed of basic, intermediate,
and acidic lavas and tephra.
Thorarinsson’s classification schemes for Icelandic
volcanoes have generally been adopted by other
geologists who have studied Iceland’s varied vol-
canic landforms. ThorleifurEinarsson’s two textbooks
on Icelandic geology, Jarbfraeöi, saga bergs og tands
(1968) and Jardfraedi (1973) and Hubertus Preusser’s
work on the Landscapes of lceland: Types and Regions
(1976) all contain variations on Thorarinsson’s earlier
two classification schemes (1959and 1968).
NEW GEOMORPHIC CLASSIFICATION
OF icelaNdic VOLCANOES
From a review of the three previous classification
schemes for Icelandic volcanoes (1959, 1968, and
1980), from an extended discussion with Kristján
Saemundsson in August 1981, from both field observ-
ations and photogeological studies oflcelandic vol-
canoes, and from modifications to a provisional
classification (Williams et al. 1981, 1982) a new
classification of Icelandic volcanos has been develop-
ed (Figs 1, and 4-6). The new classification scheme is
based on the interrelationship of the following
criteria: nature of the volcanic activity (effusive,
mixed, or explosive); environment during form-
ation (subaerial, subglacial or submarine); form of
feeder conduit (short fissure or tubular conduit or
long fissure), for the three primary compositional
classes of Icelandic volcanoes: basic, acidic, or a
mixture of basic, intermediate, and acidic (central
volcano complexes). In addition, a volcano-like
landform, the pseudocraters, is included as a
separate category.
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