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Lava-Cooling Operations During the 1973 Eruption of Eldfell Volcano,
Heimaey, Vestmannaeyjar, Iceland
U.S. Geological Survey Open-File Report 97-724
Lava Cooling1:Introduction | Nature of Lava Cooling | Summary of Operations | Personal Commentary |
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Summary of Lava-Cooling Operations
After the inhabitants of Heimaey had been safely transported to the mainland (of Iceland) within a few hours of the beginning of the volcanic eruption on Heimaey, relief activities in the town of Vestmannaeyjar were directed primarily at preventing house fires caused by incandescent lava bombs and at clearing the tephra fall from roofs of buildings because of the imminent danger of collapse from the excess weight. It soon became evident, however, that the chief danger was from the movement of lava, presenting a danger not only to the town, but also to the harbor. The harbor was [absolutely] essential to the economic lifeblood of the town [e.g., fishing].
The first attempt at cooling the lava with water was made 15 days after the onset of the volcanic eruption (23 January 1974), when lava started to approach the harbor entrance. Firemen set to work spraying seawater on the edge of the lava from powerful pumps and fire hoses which had been sent by air to Vestmannaeyjar from the fire station at Keflavík International Airport in southwestern Iceland. It was noted that the water had some effect on the lava flow, and that it exerted some control on the movement of the lava-flow front, where the stream of water was initially directed.
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Figure 3. Click on figure for larger image with caption. |
These first attempts resulted in an effort to acquire [many more] pumps, pipes, hoses, and spraying nozzles to achieve maximum effectiveness in pumping water onto the lava. Also, bulldozers were used to make protective ramparts directly in the path of the lava moving toward the town. At the beginning of February, the lava was moving mainly towards the sea, but it slowly began to turn north along the coast in the direction of the harbor entrance. At the same time the lava front was forced laterally upon the coast toward the town. The ramparts were extended along the coast from Skans [south of the outermost breakwater; see fig. 3] near Leiðarvarða, southeast to Vilpa [east of the new hospital (nýja sjúkrahúsið)] onto which sections of water pipe were laid. Attached to the primary water pipe were fire hoses that were tipped with the customary fire nozzle to spray water onto the lava margin. The water jets caused rock pillars to push up out of the viscous lava and become separated, making a mound of rubble at the lava front. When the lava front moved imperceptibly towards the rampart, the rubble strengthened the rampart and formed a strong impediment to the advancing lava front, but they did not prevent the molten lava from welling up behind the margin, gradually causing the lava front to grow in height. Molten lava also oozed from the lava front but never traveled very far before being solidified by water. [As a precaution] the movement of the lava front was monitored day and night.
This long and tenacious struggle was maintained for more than a month. By the end of the month, however, the lava front abutted the rampart along its entire length and, at most places, was somewhat above it. The lava front grew to a height of about 20 m and still posed a hazard. A maximum volume of about 100 l s-1 of water were pumped on to the 500 m-long lava front, but, because the water ran off the lava before turning into steam, it was not as effective as expected. Where it was desired that the water should reach over the 20-m high lava-flow front to the active lava margin, the pumps were not powerful enough to do so. Also, it was difficult to move water lines up the face of the lava front, because it was steep, loose, hot, and did not solidify quickly enough for hoses to be placed upon the lava margin. The result was that the solid crust on the lava front was always too thin to sustain the pressure of the lava backed up behind it. Later it turned out that the fight at this frontier had no effect on the result because another lateral lava stream eventually ran along the western margin of the lava front.
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Figure 5. Sandey and Lóðsinn pumping sea water onto the forward margin of the lava at the breakwater (Photograph courtesy of Sigurgeir Jónasson, March 1973). |
In the meantime, the lava moved slowly northward along the shore in the direction of the harbor entrance. At first the lava flow was so fast that it ran along the sea bottom. It soon slowed by itself, and the sea took care of the cooling of the volume of lava that had gone into it. This did not entirely prevent the lava from continuing to flow into the sea. The most dangerous lava flow then headed straight for the outer breakwater and threatened to block the entrance to the harbor. A tactic was adopted to try to pump seawater directly onto the terminus of the lava flow both from the breakwater and from the sea. Use was made of fire trucks, one of the harbor boats, Lóðsinn, with its pumps, and the pumping dredge Sandey which arrived at Vestmannaeyjar on the first of March [1973] (fig. 5). With this concerted effort the lava front was mostly stopped, but at the same time it started to rise and swell where the backed-up flow of lava continued. Sandey had a large-diameter-hose nozzle that was capable of directing a cascade of sea water directly upon the lava and cooling it as far as the water could reach.
The bulk of the water ran back into the sea, however, before reaching the most critical areas. In order to abate the flow of the lava, it was decided to place a water conduit in the lava field about 200 m in back of the lava margin.
This decision involved a highly difficult operation. The pipes that were used in the conduit were of steel, and because Sandey was used to pump sand onto land, they were more than 0.5 m in diameter. They could only be moved by using a bulldozer to carry them up over the still mobile lava that was glowing red-hot under its surface. However, tephra that had been deposited on the lava provided an insulating layer. This was probably the first time that a bulldozer was driven onto a still flowing lava. The first experiment was quite successful, because the bulldozer made its way up onto the lava front and was able to clear a road 100 m through the lava field in a few hours. The bulldozer driver had to be very cautious because incandescent lava fragments came to the surface right away. However, the lava showed no sign of subsiding beneath the bulldozer, even if it were in a molten state.
During a period of two days, [additional] roads were cut in two places, but the lava margin grew to such a height that the bulldozer could no longer ascend it. Another suitable spot for making a road was selected that permitted the pipe to be transported by trucks onto the lava flow. Although the workers succeeded in bolting the pipe lengths together from the pumping ship that was standing by in the inlet between the breakwater and the Skans area, it was very difficult to do so. Once the pumping began, the pipes continued to break because of the movement of the lava. It also became increasingly difficult to work because of steam that obscured the worker’s vision. Nevertheless, more and more lengths of pipe were put in place until the line extended about 200 m onto the lava, and cooling became possible across the lava tongue that extended towards the breakwater.
After pumping had continued for 15 days, using almost 0.5 million m3 of seawater, a solid barrier developed across the lava termimus stopping the flow. Many weeks later, there was still some movement in the lava just south of this barrier. The pressure became so great that the surface of the lava buckled, but its cold barrier remained intact. Had it not been for the cooling, the lava tongue could be expected to take on a lower contour, and therefore extend further along its direction of movement. Also, it might have continued to move very slowly for a whole month longer than it actually did. It failed by only about 100 m to block the entrance to the harbor.
It was two months after the start of the volcanic eruption that the lava began to flow into the eastern part of the town so rapidly that no quick measure could be taken before about one-fifth of the town had been covered by lava. The lava stream came directly from the crater along the western border of the molten mass and overran the town from the southeast. The rampart ran from Skans in an arc toward Vilpa. The lava tongue did not move very quickly at first, its terminus lying on the dike for 15 days. Meanwhile, every effort was made to increase the height of the rampart, but the lava tongue grew faster in height and bulged out along its margin. Water-cooling did not succeed there because of insufficient pressure in the available pumps because of the distance from the harbor. The rampart finally reached 12 meters in height, but the lava was two times higher. It was remarkable that the sheer weight of the lava was apparently not able to push the dike material aside, although it was composed of loose material, such as tephra that covered the lava margin.
After the lava flooded into Vestmannaeyjar, a turning point was reached in the water-cooling operations. Essentially, the experience confirmed that more pumps were needed to provide sufficient water volume and pressure. About 50 large pumps were assembled and airlifted to Iceland from the United States in a very short period of time. Up to 1,000 l s-1 of water were pumped, with sufficient pressure to be able to raise the height of the water to as much as 100 m. At this time, it was also discovered that plastic tubing produced by Iceland at Reykjalundur could be used for distributing water on the lava. At times the empty tubes melted and burned if they came in contact with hot lava, but, if they were filled with water, they could sustain the heat very well. A pipe with a diameter of 20 cm easily delivered 100 l s-1 of water. Plastic pipes were assembled behind bulldozers in 100- to 200-m lengths, and towed out onto the lava. In this way, they were much easier to position than metal pipes. Also they did not break when shifted by the movement of the lava.
The movement of the lava into the town stopped on the morning of 23 March, after it had pushed half way through the town toward the harbor. Where the rapidity of movement rendered the old pumping station useless and the new one not yet installed, there was a halt in the cooling operations. Considerable water-cooling was achieved only at the northeastern corner of the lava flow, at Bakkastígur [east-west street south of Skans], where a 100 to 200
l s-1 flow of water was pumped for an entire day, before the movement resumed on 26 March.
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Figure 6. Click on figure for larger image with caption. |
When the lava flood again ceased somewhat for the second time on 28 March, pumping from the ships was then at its full strength at the northern edge of the lava, with 300 to 400 l s-1 of water being pumped along a lava margin 350 m long. At first, water was directed through nozzles at the lava margin, but, on the third day, hoses were moved onto the lava. The lava edge moved very little after pumping on it began in earnest, and one week later it had become fairly well solidified. However, lava continued to flow into the town along a lava tongue, although it had stopped further upstream. To retard this advance, a road was laid upon the lava tongue beside the new hospital about 0.5 km south of the northern end of the lava tongue. A pipe was put in place, which delivered 400 to 500 l s-1 of water upon the lava. Cooling started there on 1 April, or four days later than the cooling at the northern edge, and the water was delivered on the lava by water jets which sprayed out 50 to 100 l s-1. On 4 April, one 100-liter jet was added, 300 m nearer to the crater, where the old Vilpa water-hole was located formerly, now buried under the thick lava (fig.3 and fig. 6).
When the cooling of the lava east of the hospital had begun, the flow velocity of the lava was only 1–2 m h-1, and the lava flow started to abate very quickly after pumping started. Because of the steam generation, however, it was not easy to absolutely confirm this observation. From this place the water ran about 250 m along the lava flow in a direction towards the harbor, forming a continuous dense cloud of steam. On the other hand, the water did not run off the lava to any extent, because the lava margin was usually higher than its inner parts.
Geodetic engineers from Landmælingar Íslands [National Land Survey of Iceland] and from Orkustofnun [National Energy Authority] kept abreast of the movement of the lava as much as possible and, moreover, changes were measured from vertical aerial photographs. On about 10 April, the movement of the lava into the town was nowhere more than about 1 m during a 24 hour period. Water-spraying operations onto the lava east of the hospital were reduced to 200 l s-1, and the most westerly portion of the lava stream that ran out from the crater's mouth began to be cooled by means of two 100 l s-1 water jets. At that time the outflow from the crater was at peak force at the western bank, with a speed of about 2 m h-1. The effect of the cooling was quickly noted, and next day the lava solidified not only where the water jets were located, but also in the direction of water movement which extended 100–200 m along the lava flow-front, cooling it rapidly. The surface of this lava became very rough and very conspicuous. It is on top of the Kirkjubær farm and would aptly be named the Kirkjubæjahraun [Kirkjubær lava].
By the middle of April, continuous cooling was achieved on the lava flow that had flowed into the town all the way from the crater. At the northern edge of the lava tongue that extended towards the harbor, a completely-cooled zone had been created. The water-cooled zone extended 50 m onto the lava, and then the cooling was stopped. There was no risk that the lava flow would move again at the cooled zone, but without water cooling it probably would have continued to flow for many weeks at full force. Then the lava flow within the town would have continued to rise and bulge out, surge forward several times and descend into the harbor.
Easter week proved crucial to the progress of the lava flow. The flow westward from the crater stopped gradually, probably from the effect of cooling; at the same time, however, the lava flow from the crater also stopped, and a solid threshold piled up at the crater's edge. Probably, lava started to rise until the pressure became so strong that something had to give way. On 22 April (Easter Day), lava surged from the crater, flowed to the east, as lava poured out of the crater under the rock rim and flowed to the east and south alongside the crater cone, where some of it flowed towards the sea. After that episode, lava flowed only within that confined channel. Lava flowing out of the [Eldfell] crater essentially stopped at the end of May or the beginning of June, 1973.
Apparently, the possibility of the lava breaking out towards the west rather than towards the east seemed to be about equal, but the water cooling might have made the lava more solid on the west side. If the lava flow had come out to the west and freely extended its path directly down into town, the volume of lava that flowed in that direction was certainly sufficient to inundate the entire center of town and fill up the harbor.
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Figure 11. Click on figure for larger image with caption. |
By now the lava was cooled in [10] areal segments [fig. 11] by moving the spraying operations east onto the lava, until it had reached a line heading from the western edge of the Eldfell crater north just east of Ystiklettur [hill on the north side of the harbor entrance]. Water was also pumped from two pumps onto the edge of the lava extending to a spot facing Ystiklettur. The lava was forced to stop moving, even though it was still molten in this area and had even entered the harbor mouth especially at Ystiklettur. In the beginning of May the entire 0.5 km2 area was stationary.
Furthermore, water pipes were put closer to the crater than before or as close as 150 m from the vent. Fire hoses and nozzles were connected to the pipes in case the lava started flowing from the crater along the gorge which had formed on the western edge of the crater mouth. A few lava streams issued from there, but were so small that they stopped by themselves, thus cooling was never really carried out at this location.
This last sign of life from the crater occurred on 26 June. On 2 July I descended into it and found the bottom cold and concealed by rock slides. Water-cooling operations were ended completely on 10 July, and, by then, about 6 million m3 of seawater had been pumped onto the lava. According to what was said earlier in my lecture, it may be calculated that the water had converted about 4 million m3 of molten lava to solid rock. Adding everything together it may be estimated that about 250 millon m3 of volcanic material were erupted.
Temperature measurements in five boreholes that were bored in the lava in May and June (1973) showed that the cooling had conformed closely to theoretical calculations. In the borehole nearest to the lava margin at Fiskiðjan hf. (fish-packing company), no molten lava was found. In the borehole east of the new hospital there was solid rock down to a depth of 13 m; the same was true of the borehole in the lava over the now buried Vilpa waterhole. In the lava tongue at the harbor entrance, which the Sandey had cooled, cooling extended to a depth of 15 m. Only at one site was molten lava found directly under the loose scoria. It was in a hole bored in an uncooled part of the lava tongue where the former intersection of the roads from Austurhlíð and Urðarvegur was located. There, molten lava was encountered at a depth of 5 m, while the boring was continued down to about 17 m. On 13 July, the temperature in this hole was measured at 1,050 ºC, whereas the highest temperature of flowing lava during the eruption was measured at about 1,080 ºC.