Jökull - 01.12.1983, Side 24

Fig. 3. Oblique aerial photo-
graph of one of the 21 basalt
volcano landforms, the Maar
Row, Valagjá, about 15 km
NE of Hekla. Photo No. 22-
23 taken on 12 July 1979 by
Richard S. Williams, Jr.
View looking SSW.
ICELANDIC TYPES OF BASALT
VOLCANOES
Fig. 1 shows the Icelandic types of basalt vol-
canoes, a class which includes 19 díscrete land-
forms. Under effusive activity there are eight
landform types based on the lava Shield. Eldborg
in Hnappadalssýsla (Fig. 2), a Lava Ring, appears
to be an abortive Lava Shield . Twelve landforms
fa.ll under mixed activity; four landforms are
classed as explosive in origin. Nearly all basalt
volcano landforms are paired in that volcanoes
formed by eruption from central vents or short
fissures have counterpart landforms formed by
eruptions from long fissures. The Maar landform,
for example, has a Maar Row counterpart, Valagjá
(Fig. 3). There are only three exceptions: Lava
Ring, submarine Table Mountain (Stapi) and
Mixed Cone Row. These three have no counter-
parts. Each discrete landform has a type landform:
for example Table Mountain (Stapi)/ Type:
Herdubreid. Herdubreid was chosen because it’s an
• excellent example of the Table Mountain (Stapi)
landform, well known, and accessible in the field.
Iceland, of course, has many other Table
Mountains, but Herdubreid is given as the type
locality.
ICELANDIC TYPES OF RHYOLITE
VOLCANOES
Figure 4 shows the four landforms in the rhyolite
volcano class, all the result of subaerial or subglaci-
al effusive activity. The Flow Dome landform has
short and long fissure counterparts. The two types,
Fig. 4. Icelandic Types of Thyolite Volcanoes
NATURE OF ENVIRONMENT FORM OF FEEDER CONDUIT
VOILCANIC DURING SHORT FISSURE OR
ACTIVITY FORMATION TUBULAR CONDUIT LONG FISSURE
Subaerial FLOW DOME FLOW DOME
EFFUSIVE Type: Laugahraun Type: Hrafntinnuhraun
ACTIVITY Subglacial ★ Type: Sydri-Háganga ★ Type: Hlídarfjall
22 JÖKULL 33. ÁR