Jökull - 01.01.2001, Qupperneq 54

Ármann Höskuldsson
Figure 4. SEM photograph of the medium to fine ash grains that make up more than 70% of the ash–flow de-
posits. The quenching structure of the rod shaped particles, chips, and vesicle–wall fragments are indicated.
The assemblage is typical of phreatomagmatic eruption deposits and magmatic fragmentation in the eruption
conduit. Grains that are 50 micron in diameter or larger contain abundant microvesicles which indicate that
the magma was being degassed at the time of quenching. – SEM rafeindasmásjármynd af kornum sem eru
einkennandi fyrir meira en 70% af gjóskuflóðasetinu. Kælingareinkenni eru skýr á ílöngum brotflötum kubba-
og blöðruveggja. Samsetning kornanna er dæmigerð fyrir phreatomagmatíska gjósku og gjósku sem myndast í
aðfærsluæð gossins. Korn 50 micron og stærri innihalda töluvert af blöðrum sem sýnir að kvikan hefur verið
langt frá því að vera afgösuð þegar hún var fryst.
The lahar deposits
There are two main lithofacies that make up the
laharic deposit. The first facies is represented by
coarse–grained, non–bedded, matrix–supported brec-
cia deposits. The matrix consists of fine to medium
grained ash with scattered rounded pumice lapilli.
The coarse blocks within the breccia are angular lithic
fragments from the edifice. The second facies is fine
grained ash with lenses of lapilli pumices and lithics.
The unit exhibits distinctive internal stratification and
depositional structures such as dunes and megadunes.
Abundant fragments of uncharred wood occur in this
unit suggesting a relatively low emplacement temper-
ature. Both facies are valley confined where they out-
crop on the western slopes of the volcano. Neither
unit has been found to the east of the volcano.
54 JÖKULL No. 50