Lava-Cooling Operations During the 1973 Eruption of Eldfell Volcano,
Heimaey, Vestmannaeyjar, Iceland
U.S. Geological Survey Open-File Report 97-724

Title Page

Table of Contents

Editor's Introduction

Lava Cooling
by T. Sigurgeirsson

Appendix 1

Appendix 2

Influence of Cooling on Lava Temperature

Figure 16. Map showing the locations of eight boreholes, old and new, and two trenches

Figure 16. Click on figure for larger image with caption.

Five boreholes were drilled in the new lava, four in areas that had been cooled non-uniformly and one in an area which had not been cooled. The positions of the boreholes are shown in fig. 16, and the results of the temperature measurements in fig. 17 and fig. 18. Figure 16 also shows the position of trenches that were dug all along Helgafellsbraut in order to avoid having vapor [e.g., steam, carbon dioxide, and other gases] spread any farther [to the west] along the former surface [contact between the old land surface and new overlying tephra].

Figure 17. Temperature measurements in borehole I, II, III, and VIII

Figure 17. Click on figure for larger image with caption.

On 12 May, a drill was sent to Vestmannaeyjar from Orkustofnun [National Energy Authority]. The drilling proceeded well, and a total of five 10-25-m-deep holes were drilled into the lava and three into the area west of the lava edge Figure 16; one of the holes [borehole V] was 35 m deep. People from the State Drilling Contractors had the unique opportunity into drill in red-hot lava. It is only known to have been done once before in Hawaii [e.g., Alae lava lake, Kilhauea caldera, Hawaii. See Peck, D.L., 1978, Cooling and vesiculation of Alae lava lake, Hawaii: U.S. Geological Survey Professional Paper 935-B, 59 p.].

The drilling was started where the lava had been cooled the most [borehole I], for example, [just up onto the lavas south of] Fiskiðan hf. [fish-processing company]. The next borehole [borehole II] was in an area that had been cooled a little less and the 3rd one [borehole III] in an area where no cooling had been tried at all Figure 16. Borehole IV, which was close to Vilpa [see Figure 3 in the Introduction] showed very similar results as from borehole II, and, therefore, its temperature profile is not shown.

Back to Top

Figure 18. Temperature measurements in boreholes V and VI

Figure 18. Click on figure for larger image with caption.

Borehole V, VI and VII were drilled in the area where lava had not flowed, [but was covered by a layer of tephra]. These three boreholes were drilled because of the intense heat that formed in the soil west of the lava edge. The houses had started to deteriorate from the heat. [Also, the new hospital was situated just to the west Figure 16.] In boreholes V and VI Figure 18, the temperature of the soil was 100 ºC. at 10-m depth, but dropped to a near-surface [ambient] temperature in the next 5 to 10 meters. Borehole VII, which was south of the new hospital, showed on the other hand, a temperature of 4 ºC. from the surface to the bottom.

The last borehole, borehole VIII, was drilled into the lava east of Skans [Figure 3 in the Introduction], but that was the only one drilled beyond [northeast of] the former coastline of the island. Much cooling had been carried out there, within a relatively small area, when Sandey was pumping [seawater onto the lavas] there; the temperature of the lava was 100 ºC. from the surface to a depth of 13 m.

If a theoretical cooling of a lava field, based on air cooling only, is studied in order to realize how rapid the cooling is, one may look at a simple model of a smooth and thick lava field that originally was a lava flow. In the beginning, the temperature is the same all through the lava flow; i.e., 1050 ºC. Temperature measurements performed [by us] support this [theoretical calculation].

Back to Top

Figure 19. Diagram showing lava surface, temperature, original lava thickness, lava-solidification front, and solid lava thickness.

Figure 19. Diagram showing the lava surface, temperature (T) profile, original thickness of molten lava (X), lava-solidification front (dashed line) migrating downwards over time, and thickness of solid lava.

The heat-transfer-equation of solidifying rock is:

Table 4a showing formulas

If the following value for specific heat at constant pressure for solidifying rock is used:4

Table 4b. showing formulas

one arrives at an answer that is shown in figure 20, where the depth of the lava in meters is a function of the time in years.

Figure 20. Graph showing normal rate of cooling of lava over time with depth from the surface

Figure 20. Click on figure for larger image with caption.

The two plus signs on figure 20 show the temperature in borehole III, where the lava was not cooled. Theoretical cooling of the lava is slightly faster than this result of measurements indicates, because the effect of rainfall was not taken into consideration. Average rainfall in the Vestmannaeyjar is about 1.5 m a year, which corresponds to the cooling of one meter of lava down to 100 ºC. a year, if all rainwater vaporizes. If the effect of the seawater cooling from the holes drilled is studied, it will be noticed that the cooling was 50-100 times faster in those areas compared with self-cooled lava.

Previous Page

Title Page

Back to Top

Next Page

[an error occurred while processing this directive]