Jökull - 01.12.1967, Blaðsíða 46

The Lakes Stórisjór and Langisjór
HAUKUR TÓMASSON and ELSA G. V I LMU N DARDÓTT I R,
NATIONAL ENERGY AUTHORITY, REYKJAVIK, ICELAND
ABSTRACT
The history of Stórisjór and Langisjór is dis-
cussed and the chief records on the lahes are
compared. Stórisjór is considered to have been
situated in the Tungnaá depression and iri-
vestigations show that it was a clear-water lake
up to about 1600 wlien it became contaminated
xuith glacier water as a result of glacial advdnce
in the “cold climatic period”. Lake terraces
found at Langisjór representing periods of
higher lake level clue to glacier advatice are
also discussed. Glacier oscillations are found to
have been rather extensive since the coloniza-
tion of Iceland.
1. INTRODUCTION
The present paper on the lakes Stórisjór and
Langisjór is compiled from two reports publish-
ed by the National Energy Authority in the
year 1967. Both these lakes have been under
consideration as reservoirs for power plants in
the Thjórsá and Tungnaá rivers. In connection
witli the storage of water from Tungnaá the
main difficulty remains to find a suitable dam
site for the creation of a reservoir. For that
purpose a search for a site has been carried
out all the way from tlie Vesturbjallar moun-
tains to the confluence of the river Lónakvísl.
The uppermost dam site, at Lónakvísl, is the
only one, which has been investigated by drill-
ing. The main difficulty connected with using
Langisjór as storage is on the other hand that
glacier water lias ceasecl to flow into it because
of the rapicl retreat of tlie Skaftárjökull glacier
in the last decades. This lias greatly weakened
the arguments for the use of Langisjór as a re-
servoir.
The name Stórisjór (Big lake) is copied after
the denomination of a lake supposed to be
found in the Veidivötn area. The lake is men-
tioned in a travel account dating from 1795,
otherwise it is a kind of a legendary lake. At
the close of the last century this lake was
searched for, but coulcl not be found and vari-
ous suggestions as to the origin of the name
have been made. A thorough discussion of
Stórisjór is to be found in the Icelandic sum-
mary, but as maintained in chapter 4 we con-
sider Stórisjór to have been situated in the
Tungnaá depression.
2. GEOLOGIC SETTING
The main characteristics of the surroundings
of Veidivötn lakes group ancl Langisjór are:
1) A dominant NE—SW lineament of all topo-
graphical features such as lakes, rivers, moun-
tains and faults. 2) Geologically very young
bedrock, móberg ridges from the Quaternary
period and postglacial lava flows and volcanoes.
3) A great number of lakes in depressions
reaching down below the ground water table.
Most of the lakes receive very little surface
water and many are altogether without surface
drainage because of the porosity of the bed-
rock. The depressions occupied by the lakes are
mainly formed in three ways: In the first place
as crater lakes. Most of the crater lakes are in
the Veidivötn area, e.g. Stórafossvatn. Secondly
as depressions in móberg mountains (Laufdals-
vatn). Thus the biggest lakes are situated in
depressions between móberg ridges (Langisjór).
Thirdly as lava-dammed clepressions (Litlisjór).
3. HISTORICAL ACCOUNT
The group of lakes scattered over the area
between the Skaftá and the Kaldakvísl rivers
on both sides of the river Tungnaá seems to
have had the name Fiskivötn (Fish lakes) in
olden times. Tlie olclest record in which the
name appears is the saga Njála, which is sup-
280 JÖKULL 17. ÁR