This week’s geoscience digest is, to say the least, serendipitous. Normally I like to pick up on a single theme if I can, but this week the news items that have caught my eye have been so wide-ranging that I’d struggle to establish anything other than the broadest link between them
They aren’t even all on the Earth. So this week (in addition to the weekly update on Kilauea) we’re looking at an earthquake in Indonesia, ice cores in the Antarctic and right off-planet to the subject of water on our near neighbour, Mars.
The Week’s Biggest Earthquake
It’s been a while since I looked at a large earthquake, but this week the headline news was the sobering tale of a fatal event in Indonesia, on the island of Lombok. The cynic in me wonders if it would have been quite so newsworthy of it hadn’t happened in a tourist area popular with readers of the media in which I spotted it, but the facts are sobering — that at least 16 people were killed and over 300 injured.
A quake of this magnitude (M6.4) in this area, along the southern edge of the Sunda plate, is nothing unusual. It’s a tectonically-complicated area, though, with lots going on. On a major scale as the Indo-Australian plate converges on Eurasia (broadly north-south) while the Pacific plate and Philippine Sea plate move westwards, trapping a lot of crust between them in the congested area between mainland south-east Asia, Indonesia and the Philippines.
The Lombok earthquake was a shallow one (at 6.4km) and its mechanism indicates that it was caused by convergence. The island of Lobok lies at the eastern end of the Sumatra subduction zone, but the earthquake was too far from the trench, relative to its depth, to be the result of movement at the subduction zone.
An alternative cause might be the smaller Flores Thrust, which lies to the north and which dips southwards. The epicentre of the earthquake was around 40km south of this, which is again probably to far for the tremor to be caused by direct movement at the fault.
The Flores Thrust appears the most likely source but in fact the tremor is probably the result of shallow deformation as the two subduction zones, which at this point are around 350km apart, move very gradually together the crust between them readjusts.
Mars: The Next Frontier?
Is there life on Mars? Who knows? But we’ve long known that life requires water, that Mars has ice caps and that the evidence of erosional features indicates that water has, in the past, been present on the Red Planet. Scientists have suspected for a long time, too, that the water is still there, though not as we see it on Earth, flowing on the surface as rivers and lakes and falling to earth as rain.
This week there’s exciting new evidence for Mars geeks. Research published in the journal Science has provided evidence that there is “a stable body of liquid water” beneath the planet’s south polar ice cap — something that has been suspected for decades but for which no real evidence had previously been produced.
This doesn’t mean we’re ready to hop on the next space shuttle to Mars — far from it. The feature which is identified as a probable subglacial lake (resulting from basal melting of the ice) is only around 20km across. The limitations of the instrumentation mean that smaller bodies can’t (yet) be identified but that doesn’t mean they don’t exist and, as the report notes: “there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location”.
Scientific discovery is an incremental process, and single discoveries that change everything are few. The majority of them are made step-by-step, with the eventual ‘discovery’ being built upon thousands of previous research papers, hypotheses and experiments. This isn’t as mind-blowing a discovery as the news media might make it seem, but it is another step in a long process — and who know where this discovery may lead?
The Oldest Ice
If I were to establish a tenuous link between at least two of the items in this digest, it would be to do with remote data sensing of polar ice caps. The one above was on Mars, but there’s research of equal importance going in in the southern polar regions of our own planet.
I’ve mentioned before that recent research has established new data for the coldest temperatures on the planet. Researchers are now using radar to try and identify drill sites to enable them to access the oldest ice on the planet and, by so doing, help to learn more about past climates and the present processes of climate change.
Ice cores contain invaluable information about the atmospheric conditions in which each molecule of ice was formed, and they go back a long, long way — in some cases, hundreds of thousands of years. Analysis yields information on such things as global and regional temperatures and atmospheric composition, as well as evidence of event such as dust storms or volcanic eruptions.
The older the ice, then, the better the information. In 2017 the oldest ice discovered so far was revealed at a staggering 2.7 million years old, but the record wasn’t continuous — in other words, pieces of the record were missing. The current holy grail of palaeoclimate research is the recovery of a continuous core of ice which is 1.5 million years old — and the identification of the possible locations for such a core is what the most recent research has revealed.
Not a lot is happening at Kilauea that wasn’t happening previously. The cycle of lava flowing from fissures (currently only Fissure 8) in the East Rift Zone to the sea, with regular crater collapse at the summit, continues pretty much unchanged.
The results of the eruption are, of course, cumulative and the Big Island is, as a direct consequence of the eruption, getting bigger. I can’t find any figures for the increase in area — and they would, in any case, be out of date by the time they were published — but a comparison of the maps published regularly by USGS and the satellite imagery freely available on Google maps and the like is an indication of how dynamic our planet truly is.