The destruction wrought by Kilauea’s eruption continues apace, while scientists continue to monitor the ever-evolving volcanic violence. It’s already put on quite a show: we’ve had volcanic thunderstorm clouds, volcanic tornadoes, explosive eruptions at the summit crater, blue fire, volcanic haze, and most recently, the construction of new land as the last fissure standing, number 8, continues to dump its lava into the ocean.
As first spotted by LiveScience, and explained by the ever-remarkable United States Geological Survey (USGS), lava began to invade Green Lake – within Kapoho Crater – and naturally began producing quite a large steam plume back on Sunday, June 3.
“By 1:30 pm the steam plume had ceased and by 3 pm, a Hawaii County Fire Department overflight reported that lava had filled the lake and apparently evaporated all the water,” the advisory explained. That’s right: an entire lake’s worth of water had been completely vaporised by this invasion of lava.
Boiling away a lake with lava, by the way, isn’t as easy as you think. It requires a boatload of energy, because water has an extremely high heat capacity. This means it requires a lot of energy per unit of water to increase its temperature by a single degree, compared to other substances.
That’s why it takes a long time for seawater to get warm in the day – it needs a fair bit of exposure to sunlight first for those molecules to vibrate enough. So, with that in mind, here’s a cool back-of-the-envelope calculation for you.
First, let's assume the freshwater lake here is full to the brim, and is a perfect hemisphere. According to Wikipedia, it's 61 meters (about 200 feet) deep, but according to state files, its 6.1 meters (20 feet) deep. Just to play devil's advocate, let's put its depth at 30.5 meters (about 100 feet). That means it contained about 59,423 cubic meters (2.1 million cubic feet) of water, give or take.
Based on the specific heat equation, and assuming the lake temperature is around 18°C (about 64°F), it would require 20.4 trillion joules of thermal energy to get the entire contents of the lake to boil.
That’s roughly the energy released by the explosion of a thousand tons of TNT. But wait – there's more.
As pointed out by Ben Edwards – a professor of geosciences at Dickinson College – to me on Twitter, I didn’t include the heat of vaporization, the energy required to transform a liquid substance into a gas at a set temperature. For 1 kilogram of water, it takes 2.26 million joules to do just that, which hints at how much more energy it takes to break apart molecular bonds than to simply heat something up.
This would bring the total energy requirement to 146 trillion joules, or 1.46 x 1014 joules. That is roughly 35 kilotons of TNT, far greater than the energy unleashed during small nuclear weapon blasts.
So, if you needed a reminder of how literally hot lava is, there you have it.
It’s worth remembering that as this eruption has progressed, it hasn’t just involved the as-predicted focusing of the lava flow out of just one single vent. The first magma that came to the surface was a colder, older batch with less gas.
Now, Kilauea is tapping mantle temperatures, ejecting lava that is as hot as lava on Earth can realistically get – about 1,204°C (2,200°F). At the moment, gas-rich fury is being fired high into the sky, and even building its own baby volcanic cone around Fissure 8, while much of it continues to be dumped in Kapoho Bay along multiple entry points.
As with the lake invasion, this is creating plenty of laze, which contains hydrochloric acid droplets and glassy volcanic debris. As ever, people are being kept away from the laze and the somewhat unstable new delta that's being born along the lava-smothered coastline.