Journalism is about impressions; science is about numbers. VC is standing in between these. We appreciate the immensity and power of volcanoes (and also appreciate that relatively speaking, these are manageable disasters. The human impact is awful for people concerned, but is not on the scale of major earthquakes or tsunamis. On balance, volcanoes create more than they destroy). But we also like to understand what is happening, and that means looking at data. Bear with me if numbers aren’t your thing! (But if that is your situation, I recommend you steer away from lotteries and stock markets, and keep a healthy suspicion of banks and car-dealers.)
The people living in Leilani were not told about any volcanic risks when the sites went up for sale. VC user quinauberon unearthed a 50-years-old advert which paints a very optimistic picture of the future of the area. (It also lists a misleading price that is only a down payment – something that in many places would now be illegal.) They could have found out the real risks by asking insurance companies – those always know. I once did a small bit of research on life expectancy of smokers, using a new method. It showed that smokers lived on average ten years less than non-smokers. Afterwards, I found life insurance rates and used them to derived life expectancy. It gave exactly the same number. Insurance companies always know best – but do not expect them to volunteer their data: they make a living by not telling you the real risks. One of the comments on this site gave a quote for volcano insurance for a house of 3000 USD per year. (That would be just for the event of lava overrunning your property: a bush fire started by nearby lava would be covered under fire insurance). That number suggests that the insurance company didn’t expect Leilani to last much longer than 100 years.
But this is in the past and now everyone knows the risks. There is an opportunity for an investor with unneeded cash to buy property in the area at a knock-down though realistic price. (Perhaps this should read: a knocked-down price.) (And of course, there is a second housing estate in the area, Nanawale estates which is not currently in the line of fire but build in an equally lava-ravaged environment. I just mention it.)
This is the importance of numbers. Can we put some more numbers on the current eruption? How does it compare? Are we talking world-cup size or also-ran?
The eruption started on May 3rd and has lasted three weeks so far. Puna eruptions in the past have been as short as one day (1961), so this is already more than some. The famous 1840 eruption lasted 24 days – we are getting close. The 1955 event lasted 88 days, and the 1960 one 36 days. Of course, Pu’u’O’o dwarfs them all: it lasted 12,870 days. Eruptions closer to Kilauea can last longer, but in Puna, 1-2 months is typical. From that, one can expect that we are half-way through the current eruption, with an uncertainty of a factor of 2: it could end tomorrow or it could continue for 2 more months, but based on past events, any longer would be less likely (not a Lurking ‘black swan’: we don’t have enough data to compare with Australian wildfowl).
The fissure activity has begun to migrate, with the most distant fissure losing pressure and one in the middle firing up. That is a sign that we are past the peak. Halfway may not be a bad guess.
A typical Puna eruptions resurfaces 10km2 with tough yet a tad uneven asphalt. As we have seen in this eruption, a lot of that comes after the initial phase, once the old sticky stuff has been dislodged and the hotter, more fluid lava starts to arrive. How are we doing up to now?
Here is the most recent HVO map. The pink shows the extent as determined on May 21, and the arrow shows the enlargement from the flows coming from fissure 15 (or thereabouts) a day later. The flow from fissure 17 has probably stalled and perhaps ceased. We also know that the lava is encroaching on the PGV but that is not yet on the map. Fissure 23 (near 5, just inside Leilani) was reported as fountaining and may be start to feed a lava flow to the southwest if it can find a slope.
The full length of the line of active or inactive fissures amounts to 6 km. Assuming that a width around it of 100 meter is covered in lava gives an area of 0.6 km2. The flow northward of fissure 8 extends about 1.5 km and is about 200 meters wide, so that is 0.3 km2. The flow from fissure 17 southeast-ward is 2 km long and 300 meters wide, so 0.6 km2. The area between fissures 20 and 17 I is almost fully covered: I estimate this as 1 by 2 km, or 2 km2. The area between fissure 15 and 20, down-slope until where the lobe starts, is roughly 2 by 1 km, also 2 km2. Finally, the two lobes to the ocean I estimate as 3 by 1 km, or 3 km2.
Adding all this together gives a current area of the lava of 8.5km2. This is rather rough and may be under- or overestimated. But it seems that this is now becoming a fairly typical-sized Puna eruption. To get into Olympic-sized territory, it needs to at least double in area. However, if more of the fissures re-activate, that is not inconceivable.
(Note added: the area is today reported as 1700 acres which is around 7 km2. The number given here was not a bad estimate.)
The images of the eruption show very nicely defined lava channels: rivers of lava in well-constrained beds. This is one of two modes of lava transport away from a vent. The other mode is through lava tubes. Lava channels cool faster (as they are exposed to the air) and therefore carry the lava less far. As long as these channels are present, the flow field can widen quite easily. Once lava tubes form, all the expansion will be at the lava front.
This is anyone’s guess! Assuming that the lava everywhere is 5 meters thick, the volume times the thickness gives an erupted volume of a bit less than 0.05 km3. But this is probably an overestimate. A volume of 0.1 km3 is quite typical for a Puna lava flow and that may be where we are heading.
How much magma was injected into the rift below Puna? We can guess from the lava lake at Halemaumau: assuming a 200 meter wide crater, in which the lava was lowered by 400 meter, the amount lost is around 0.04 km3. Pu’u’O’o also lost its lava but this was a much smaller source. The lost magma is stored in the rift. Assuming a dyke 1 km tall and 20 km long, it would require 0.02km3 to fill it. Much of the new magma will thus still be inside that dyke. As the pressure becomes lower, the dyke will narrow and will try to push some of this magma out: this can give eruptions at unexpected locations, up-rift, which can be significant but cannot match the output of the main eruption. Part of the ‘dyked’ magma will fail to come out and remain in situ after the events have ended, and form the sticky stuff in future eruptions.
How does the lava production compare to international standards? The king of lava is Iceland: it produces around 20km3 per millennium, or 0.02 km3 per year. The rate for Kilauea is difficult to calculate because it varies so much over time. Between 1840 and 1950, lava was produced at a rate of 0.01 km3 per year. After 1950, this jumped to an average of 0.05 km3 per year. Over the combined period, Kilauea can match all of Iceland! Add Mauna Loa, and Hawaii’s rate become twice that of Iceland. Not bad! (The reason is that Iceland is a spreading rift zone: 90% of its magma is used to fill the spreading rift and never gets anywhere near the surface. In Hawaii, most of the magma comes up, as it has nowhere else to go.)
If this was a newspaper article, we would now state how many Olympic-sized swimming pools this eruption would fill. This is, however, not a scientifically accepted unit of volume. In fact, it varies from pool to pool, as only the length of the swimming pool is specified in the rules of the Olympic games, not the depth. But let’s say it is 2.5 million liters, and you find that the Puna eruption so far would have filled 20,000 of them. As we only need one such pool every four years, that would have taken us to the year 7,018 AD before all the recipient pools were build. By this time the lava would have been stone cold, difficult to get into the pools and not easy to swim in.
Volcanoes are prolific energy producers. In fact, the main scale used to classify volcanic events, the VEI scale, is a measure of explosive energy.
This scale has one obvious problem: the units don’t match. The main number is the volume of tephra production. But energy should be measured in Joule, not cubic (kilo)meter. And if you want to use the power, that is energy per second, so it becomes important how long an eruption lasts. The Pu’u’O’o eruption produced more than 4 km3 of lava, but it lasted more than 30 years. It therefore is not count as a VEI5, even though there does not appear to be a specific rule that forbids this!
The Kilauea summit eruptions produced tephra: judging from the images, there is a layer a couple of centimeters thick over an area of a few square km. That brings the summit up to VEI1 -perhaps VEI2 at best.
How about the fissure eruption? On the scale above, that would be a VEI3 by now. However, one should note that the ejected volume in the table should be tephra, i.e. pulverised rock. The fissure mainly put out lava – molten, not pulverised rock. If this has been tephra, it would be a few times larger in volume, i.e. VEI4. But it is clear that a scale devised for explosive events gives nonsensical results if applied unthinkingly to effusive eruptions. Can we do better?
Let’s work with the number of 0.05 km3 of lava ejected in Puna, and let’s assume it has a temperature of 900 C above the normal Hawaiian temperature. The energy needed to heat 1 kg of lava by 1 degree C is 1000 Joule. The lava weighs rather more than 1 kg. 1 m3 of lava weight 2500 kg, and therefore 0.05 km3 weighs 1.25 x 1011 kg. To heat this by 1 degree C requires 1.25 x 1014 Joule. To heat it by 900 C therefore takes 1.1 1017 Joule. This is how much energy the lava carries! The Puna geothermal plant would have taken 100 years to produce this much energy. They may have missed an opportuinity.
This is the thermal energy in the lava. There is also energy needed for the melting itself, called the latent heat. This is in addition to the energy needed to heat it to the melting temperature. It takes 4.0 x 105 Joule to melt 1 kg of rock. For the amount of 0.05 km3 of lava, the energy needed to melt it is 5 x 1016 Joule. Add this to the thermal energy, and you get a total energy content of the lava of 1.6 x 1017 Joule. Enough to cover the entire energy requirements of humanity for a few weeks.
The potential energy can be added: assuming it erupts at 500 meter and flows down to sea level, this generates an amount of energy equal to mass times height times gravitational acceleration, and give 600 TJ. This is significant in itself but pales in comparison to the heat.
Now the fun bit. This amount of energy is equivalent to around 40 megatons TNT. The largest nuclear bomb ever detonated had a yield of 50 megatons. Puna is suffering the impact of an event with an energy close to that of the largest weapon humankind (or unkind) has ever created. That give some perspective to what the people there are living through!
How does that compare to the VEI scale? We need to calibrate it to another eruption with a VEI number. USGS has reported that the explosion of Mount St Helens was equivalent to 7 megatons, with an additional 17 megatons of thermal energy. That eruption produced about 1 km3 of tephra making it a VEI5. Puna has (so far) produced about twice the energy of St Helens. If this energy had been used in the same way as St Helens, i.e. a thermal to explosion energy ratio of 2.5:1, this could have produced a 2km3 tephra cloud. To get above 10 km3 would require a five times larger eruption. That seems unlikely at the current time, and it remains in VEI5 territory.
I therefore declare the Puna eruption of 2018 to be equivalent to a VEI5. It is world cup territory – but likely to be knocked out in the group stages. In that respect, perhaps Puna is a bit like little England.
Albert, May 2018