Quantity of water
Figure 8 shows the quantity of water, which was pumped on the lava. It is given in liters per
second (I s-1)as a function of the number of days from the start of the eruption [23 January 1973].
Figure 8. Click on figure for larger image with caption.
As the figure shows, the pumping began on 7 February, or 14 days after the beginning of the volcanic eruption, but on a very small scale. The quantity is considerably increased when the dredge Sandy started to pump (fig. 9). To be sure, the pumping was not continuous as the
diagram shows, but it is estimated that it [Sandy] pumped [at a rate] equivalent to 400 I s-1
uninterrupted for more than 10 days. Actually the pumping lasted more than three weeks. It is
estimated that the Sandy pumped about 0.4 million metric tonnes of seawater onto the lava up to
23 March, and other pumping equipment [contributed] about 0.1 million metric tonnes.
Figure 9. Click on figure for larger image with caption.
When the lava flow advanced on 23 March, there was a two-day interruption in the pumping,
while the pipes had to be repositioned, but 200 I s-1 were then pumped for 24 hours in between
advances of the lava.
On 28 March, pumping was started again and from then on it was continuous until the 168th
day of the eruption [10 July 1973], when the pumping was terminated. It is estimated that during
this time a total of 5.7 million metric tonnes of seawater was pumped after lava started to flow
over the town. A total of 6.2 million metric tonnes of seawater was pumped in all.
As may be seen from the diagram, the pumping reached its peak on 4 April, when all of the
pumping equipment received from the United States had been connected (fig. 10). This quantity
gradually decreased. The reason for that is basically that the pipes had to be constantly moved
further onto the lava, closer to the crater, so that the pressure drop in the pipes, as well as
increased height, caused less efficiency [loss of head due to friction]. Cooling with seawater was
stopped around the middle of May, and the quantity decreased about 100 I s-1.
Figure 10. Array of gasoline and diesel engines deployed on Básakers Wharf (Heimaklettur in the background) to power pumps used to cool the lava flows. Photograph by Valdimar K. Jónsson.
After the middle of June, it was decided to stop the cooling in stages, so that each week one
pumping unit was disconnected, and the engines and pumps were cleaned. The first units
disconnected pumped comparatively farther onto the lava and, therefore, relatively less quantity
than those closer to the town that were stopped later.
Figure 11. Click on figure for larger image with caption.
Figure 11 shows how much seawater was pumped onto the lava at  different locations [on
the lava flows]. [Area K was not cooled.] These locations [10 areas: A-J] represent, so to speak,
a continuous area measuring about 0.45 square kilometers that corresponds to about a nine-meter-thick layer of lava that has been cooled down to 100 ºC. on the average. However, this
does not give a wholly accurate picture, because some places were cooled more than others. The
area above the [fish-]processing plants and a lava field just north of the crater were cooled most
markedly. Considerable amounts of seawater was also pumped around Flakkarann ["The
Wanderer"], that was for a long time moving slightly. On the south side of Flakkarann, there was
a large amount of steam rising as a result of convective currents.
Additionally, it may be mentioned that salt accumulated on the lava from the pumping. This
can be easily seen where there are great patches of white on the lava. It is estimated that 220
thousand metric tonnes of salt were deposited on the lava.