Jökull


Jökull - 01.12.1985, Side 45

Jökull - 01.12.1985, Side 45
Fig. 12. Recent, (July 1984), view of the section in the gravel quarry N of Arnheiðarstaðir at about 50 m alti- tude. The original pair of exposures has now been destroyed, but this sect- ion still shows the main characteristics of the variably dipping sand and gra- vel beds. - 12. mynd. Setlög í malar- námu norðan við Arnheiðarstaði. suggest that, in fact, the material was deposited by water flowing in the regional direction into the chan- nels, implying that this flow was englacial and subgla- cial. This hypothesis is considered in more detail below. To the N of the Hnaus spur the situation of the Hof farm is rather similar to that at Skeggjastaðir, with some of the cultivated land rising in an embayment N from the lake shore into channels running over and to the E and W of the steep Ásklif ridge. Just above newly cultivated land in one channel there is a bank of rounded material, but no section is visible. After follow- ing the main channel near the crest of Ásklif the road passes through a cutting and quarry of current-bedded sands and gravels above the Ormarsstaðaá stream at about 60 m, while to the N of the stream the sheepfold is on similar material at about 50 m, at the entrance to the circular embayment in which much of the Ormarsstaðir farm is located, (Fig. 2). This embayment has many of the characteristics already described at Skeggjastaðir, being bounded on the N by the slope up to the Fellaheiði plateau and by a spur running from it to the lake shore. Channels run from the embayment itself and round it, over the ridge to the N. There are probably six parallel channels, but the most prominent visual feature is a 500 m wide shelf right above the W side of the homefield, rising from 105 m at the front to 135 m at the back against the main slope. This shelf connects one of the channels running to the W of Ásklif, at its lower end, to the end of one of the channels into the spur, at its upper end. Where it enters this upper channel the slope increases and at the break of slope is a long, wide heap of rounded pebbles and cobbles in a sandy matrix. Two narrow gullys run from the N edge of the main homefield towards the spur, at two different levels, and then widen out into two long, narrow lakes, before rising again to the spur. What appear to be eskers are found both below and above the lakes from about 90 m up to 125 m. All this would seem to justify the theory of water flow in subglacial channels and the formation of eskers, in that these features are not found near the crests of channels but are deposited as the result of rising flow, (Shreve, 1972). Just below the point where Ormarsstaðaá plunges over the edge of the Sigurðargerðisbjarg cliff to cut through the channel system, on a channel floor over- hanging the new gorge cut through it, lies another heap of rounded stunes in a sandy matrix. It is of interest that most of this 4 km wide system, except for the shelf mentioned above, is only visible from a higher level. From Ormarsstaðir northwards, Lagarfljót bends more to the NE and the distance between the lake shoreline and the higher ground to the W increases. Banks of rounded material are less apparent but esker structures may occur within the channels or below ground level generally. Some distance to the N, in the steep S bank of the Rangá stream at the side of the road bridge about a kilometre from the junction with Lagar- JÖKULL 35. ÁR 43
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