Jökull


Jökull - 01.12.1985, Page 54

Jökull - 01.12.1985, Page 54
Fig. 1. The Upper Borgarfjörður regi- on and the major thermal fields of the Reykholt and Baer thermal systems. 1. mynd. Yfirlitskort af ofanverðum Borgarfirði og helstu hverasvæði í Reykholtsdal og nágrenni. The main aquifers appear to be northeasterly trending faults and dykes. In the lowlands they are intersected by open northwesterly to northerly trending fractures which enable the hot water to flow to the surface. The Vellir thermal field is a part of the Reykholt thermal system and is adjacent to the Reykholt — Kópareykir thermal field, about 2.5 km further west. A detailed study of this field was requested by the Nature Conservation Council. The Vellir geyser (also called Árhver) is the only geyser in West Iceland and one of very few in Iceland still active and unaffected by human activity. This together with unusual surroundings has raised an interest in its conservation. This paper pre- sents the results of the survey. SURFACE THERMAL MANIFESTATIONS The Vellir thermal field comprises numerous hot and warm springs. The majority of the springs are spread along the 1.5 km long Vellir line, crossing the Reykholtsdalur valley from SSW to NNE. In addition the short NW-SE trending Sturlu-Reykir and Hagahús lines are located on the northern and southern sides of the valley, respectively. They may be two segments of the same line that crosses the valley, intersecting the Vellir line near the Vellir geyser. Surface geothermal manifestations were mapped in detail and the natural discharge of individual springs measured where possible. The total discharge is about 33 1/s and most of the springs are boiling. A map of all thermal manifestations is shown in Fig. 2. The tempera- ture range and discharge of the hot springs is summa- rized in Table 1 but a short description of the thermal field is presented below. The chemical composition of thermal water from four hot springs is listed in Table 2. The chalcedony geo- thermometer gives values from 126 to 133°C, indicating a base temperature of about 130°C. The difference between values for different hot springs is insignificant. Only a minor part of the hot water from the Vellir thermal field is utilized for central heating of farm- and greenhouses and no wells have been drilled so far. The Vellir Line The Vellir line has an overall trend close to N15°E and its total length is about 1.5 km. The total discharge is about 27 1/s of mainly boiling water. The Vellir line can be divided into three separate segments, termed here the northern, central and southern segments. The northern „segment" includes only one spot of warm ground (no. 1 in Fig. 2). The central segment is about 600 m long and stretches from the Badlaugahver hot spring (no. 2) in the north to the Vellir geyser (no. 7) in the south and has a trend close to N3°E. The springs are in two groups, the Badlaugahver group with Badlaugahver (also named Badlaugar) as its only major hot spring and the Vellir 52 JÖKULL 35. ÁR
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