Jökull - 01.12.1985, Page 55

TABLE 1 -.Natural discharge and temperature range of the Vellir thermal field. TAFLA 1: Vellishverasvœðið, mœldur hiti og náttúrulegt rennsli hvera.
Nos. ref. to Fig. 2 Description Discharge 1/s Temperature °C Discharge 1/s Temperature °C
1 „warm ground“ 0 11
2 Badlaugahver group 2.7 18-99
Badlaugahver 1.5 99
„springs sou. of Badlaugahver". 1.2 92
3-7 Vellir group 21±4 100-102
7 Vellir ~17 102
8-9 Hveragil group 0.2 29-86
10 Snaeldubeinsstadahver 2.7 100
11-12 Sturlu-Reykir group 6.1 58-101.5
11 Upper Sturlureykjahver 2.5 101
12 Lúsahver 3.1 101.5
13 Hagahús group — 12-53
Total 32.7
group (nos. 3 to 7), separated by a 200 m long gap
where no thermal activity is encountered. Several signi-
ficant hot springs belong to the Vellir group. Most of
them are located along the bed of the Reykjadalsá river
and thus partly submerged. The river prevents direct
discharge measurements of the Vellir group. However,
a fair estimate could be obtained by measuring the total
flow of the river and taking temperature profiles across
the river up and down stream from the springs. The
calculated discharge for all hot springs of the Vellir
group was found equivalent to 21±4 1/s of 100°C hot
water.
The Vellir geyser (no. 7), which is also known as
Árhver or Vellineshver, is the largest hot spring of the
Vellir thermal field. It breaks out in six separate aper-
tures on a small hummock or ridge on a sandbank in the
middle of the Reykjadalsá river. The ridge is 1 — 1.5 m
high and about 12 m long, elongated in the direction of
the Vellir line. When the river floods, the ridge is nearly
submerged. The ridge consists of silicified marine sedi-
ments and is transected by northerly trending joints and
fractures. The Vellir geyser usually throws jets of boil-
ing water 1 — 1.5 m into the air. It is difficult to measure
the discharge exactly but rough measurements yielded
about 17 1/s including the closest apertures in the sand-
bank. In the course of the great earthquakes in 1896,
the geyser became temporarily very active, erupting
water as high as 10—12 m (Thoroddsen 1910). By pour-
ing soap into the geyser an eruption of 5—10 m may be
initiated (Fig. 3). During eruption, five of the six aper-
tures show eruptive activity and seem to be intercon-
nected but the southernmost and largest aperture is not
affected.
The southern segment is 450 m long and has a trend
close to N15—20°E. It stretches from the Vellir geyser
to the Snaeldubeinsstadahver (Logalandshver) hot
spring (no. 10), which is the only significant hot spring
of the segment. Besides Snaeldubeinsstadahver more
than 10 minor hot springs, the Hveragil group (nos. 8
and 9), define the segment. Most of them are located in
a shallow gully called Hveragil where hot water seeps
from fractures and joints in its banks which consists of
marine sediments of Finiglacial age.
The Sturlu-Reykir Line
The Sturlu-Reykir line comprises one group of hot
springs, the Sturlu-Reykir group (nos. 11 and 12). The
line is 60—70 m long, trending N35—40°W and the total
discharge 6.1 1/s of boiling water. Its two major hot
springs are named Sturlureykjahverir. The upper hot
spring (no. 11) displayed geyser action in former times
with eruptions reaching 1-2 m every other minute. Early
this century the hot spring was covered with a concrete
roof obstructing eruptions and the steam was used for
JÖKULL 35. ÁR 53