This week, from the 5-11 July 2018, I’m going to be talking about Kilauea…again. But I’m also going to be talking about earthquakes, and landslides.
Landslides in Iceland, Japan and Turkey
Landslides, though often overlooked, are significant natural hazards. I’ve talked about this before, and it’s always worth remembering, that landslides kill.
The USGS puts the number of people killed in the US annually by landslides at between 25 and 50, while the American Geophysical Union’s landslide blog (a useful and accessible source of information) indicates that the numbers killed worldwide in 2015, 2016 and 2017 were 2,250, 2,376 and 4,164 respectively.
There are many types of landslide and many different causes, and I don’t propose to go into them in any kind of detail. But this week three contrasting news stories caught my eye (and there are more that don’t make the headlines if you look) two of them with fatal consequences.
Among the prime causes of landslides is rain. Heavy rain lubricates the ground, enabling it to flow, and resulting in destabilisation of slopes. Gravity does the rest. In Japan, heavy rains and flooding have cost (at the last count) 179 lives in just the last few days, and landslides accounted for a number of these.
In Iceland, the public have been warned to keep away from what is (debatably) the largest landslide in the country’s history. The Iceland Met Office gives its vital statistics as follows: “A preliminary estimate of the volume of the slide is 10–20 million m3. The area of the debris tongue is ca. 1,5 km2 and the debris is up to 20–30 m thick.”
The IMO gives the main cause of the landslide as “A weakness … thought to have existed in the mountain causing the mountainside to fail,” though the exceptionally heavy rainfall in the area during spring and early summer may also have contributed. Fortunately, no-one was killed or injured by this event, which occurred in a remote area.
The third event, also reported as a landslide caused by heavy rain, occurred in Turkey and involved a train derailment which killed 24 people. The actual cause remains to be determined but seems not to have been a landslide but the collapse of the embankment on which the track was built.
I include this here because while it’s arguably not a landslide but an engineering issue, there is a case for considering it as such given the probable influence of heavy rain as a factor in the collapse.
These are just three landslides this week and I include them because they made the news. But with between 200-500 fatal landslides occurring each year, it’s a salutary reminder of the risk.
Over the last few weeks I’ve been rather glad that I broadened the scope of this digest. The earthquakes have dried up and if I was writing a purely earthquake-focused article I would have been struggling.
In a typical week you can reasonably expect at least one earthquake of at least M6.0 somewhere in the world, often more. On average, there will probably be at least one M7.0+ event, and over the year you’d expect to see one of M8.0+. Of course, these are averages and there’s a lot of variation.
The United States Geological Survey’s real time earthquake map has been very, very quiet recently. The past 30 days have seen just one event of M6 or larger, and that was only an M6.1. There have been only seven in the last two months, all but one M6.2 or less.
This might seem significant, but if you take the data back over the past six months, they even out and come much closer to the average figures quoted above. In the first six months of the 2018 there were five earthquakes of M7.0 or above, all of them in January or February. At that point, had I been writing about earthquakes only, I might well have been commenting on the fact that there had been an increase in earthquake activity, but that it was unlikely to be statistically significant.
I’ve commented — as have many others — on the same phenomenon in terms of volcanic eruptions. While there are short term variations in activity of both earthquakes and volcanoes they don’t represent a trend in the way that, say, climate data do.
I promised I’d keep updating you on Kilauea and I will, although as the eruption appears to have entered a stable phase (let’s not call it dull) so we could be in it for the long haul without a lot of change to report.
Probably the most important thing is that though there’s no obvious change to the rate of activity, the eruption is showing no signs of slowing. Lava flows sometimes stall and sometimes overflow their channels, but the supply of magma continues and so, therefore, will eruptive activity in the rift zone.
Meanwhile the pattern of increased seismicity followed by an explosion at the summit crater continues. And, as a footnote, when I talked about earthquakes above, I should have mentioned that the largest in the past two months — by a considerable margin — was that which occurred at Kilauea on 4 May (at M6.9) and that the summit has experienced 47 eruptions which appear on the map as having magnitudes of at least M4.5.
As I say, there may not be anything new happening, but Kilauea is certainly not quiet.
Decoding Science. One article at a time.