Well, as has been reported in a few tweets, it appears that it’s been raining "gemstones", specifically olivine, onto the ground. Plenty, including Mashable, have been wondering if this is actually a legitimate process or not.
So is it? Possibly, but there are some caveats, including the fact that the scientists on the ground there have yet to see this for themselves.
The green "gems" you can see here are olivines, an extremely common component of volcanic rocks. This iron-magnesium mineral has its own geochemical spectrum, and comes in plenty of flavors, but they tend to be light green in color and vitreous.
It’s ubiquitous in igneous rocks with a low-silica content, like the sort that’s freshly erupting from Kilauea right now. It’s one of the first things to take solid form within the magma as it begins to cool underground.
In fact, the near-mantle derived magma that’s erupting now is as hot as you can get – around 1,116°C (2,040°F) – which suggests it has a very low silica content. This makes the appearance of plenty of olivine more likely than it did a month or so ago.
Olivine is actually already everywhere in Hawaii. Over time, as this basaltic lava is weathered down, its mineral inclusions fall out, including olivine. In fact, geologist David Bressan and volcanologist Dr Janine Krippner were quick to point out to me on Twitter that there’s an entire beach made of olivine on the Big Island.
An extremely rare sight anywhere in the world, Hawaii’s – Papakolea Beach – formed when olivine crystals eroded out of the volcanic landscape. As these grains are heavier than many others, they remain onshore while others get washed away, which eventually produces a freakishly green beach.
It’s been suggested, though, that olivine is raining down on the landscape. Is this plausible?
At present, lava is still entering the sea at multiple points in Kapoho Bay. It’s happening frequently and quickly enough that it’s making a new delta, the youngest land on Planet Earth.
This lava is coming entirely from Fissure 8, the last one standing. As Dr Wendy Stovall, a senior volcanologist with the United States Geological Survey (USGS), told us a few days back, this focusing of the lava effusions on one single fissure is typical for this kind of eruption.
The fluidity, gas-rich nature of the exceedingly hot magma is representing itself at this fissure by creating lava fountains higher than 20-story buildings, and plenty of that material is raining down on the landscape.
Plenty of this is going towards building that cinder cone you see in the USGS’s photography of the area. Some is going further afield, and seeing as this is the only source of vertical lava, the olivine is likely to be coming from here.
“I think it is just coming out either in the air – which civilians on the ground have said – or breaking free upon impact,” Krippner told IFLScience. It’s probably not down to weathering, as this “should take longer.”
If it is breaking free on impact, it’s likely escaping from pieces of freshly cooled scoria, lava-formed rock that’s peppered with very small holes called vesicles. Olivine, which has crystallized out of the magma earlier as it chilled, is just hitching a ride out of hell.
Stovall pointed out to IFLScience, however, that the presence of olivine raining down is based on a second-hand report. It hasn’t been observed by any of the USGS geologists, who have also yet to see crystals like this on the ground.
“I even had people who were in the field yesterday looking for them,” she added, noting that it is nevertheless plausible that olivine crystals could be preferentially fractionated out from the melt near the lava fountain. At the moment, then, consider this an open question.
Update: The USGS told me via Twitter that they still haven't seen this phenomenon for themselves, and the olivine doesn't look like primary deposits from Fissure 8. Perhaps, then, the olivine samples were produced by an older eruptive event and were just stumbled upon by civilians.
In response, though, Dr John Faithfull, a petrologist at the University of Glasgow, tweeted the following, below.
Again, the process is possible in one form or another, but it's not clear if they are responsible for producing the olivine on this particular occasion. We'll keep you updated if something definitive comes in!
Update (25/06): There are still no reports of the phenomenon being seen first-hand. Volcanologists working on fresh deposits say that the larger olivines being found by residents don't match up to said deposits. It's pretty much now safe to say that it's not raining large olivines down near active fissures, then - but smaller olivines could be found in ejected clumps of lava, as discussed above.