Any geologists?

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GV27

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#236234 24-May-2018 18:39

Hi All,

This might sound a bit naff, but I've been prodding around Geonet and all of the volcanoes are monitored using seismographs and RSAM/SSAM.

I know what a seismograph is and it's pretty easy to get your head around it.

But can anyone tell me what RSAM & SSAM are showing and how to interpret it? I've searched for a basic explanation and even the Geonet one is over my head.

https://www.geonet.org.nz/volcano/monitoring/ruapehu

(bottom set of graphs)

Thanks,

GV27

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#2022018 24-May-2018 19:00

I guess this info is what you've read? Clear as mud.... yeah

People often mistake me for an adult because of my age.

Keep calm, and carry on posting.

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tdgeek

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#2022024 24-May-2018 19:10

Not naff, but super interesting. If there was a 4 hour doco.....

GV27

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#2022029 24-May-2018 19:17

Stu:

I guess this info is what you've read? Clear as mud.... yeah

I mean...I understand the "Day of Month" bit.

I think part of the issue is that I keep confusing it as showing depth when it's just showing 'a thing happening'.

Fred99

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#2022163 24-May-2018 22:52

GV27:

Stu:

I guess this info is what you've read? Clear as mud.... yeah

I mean...I understand the "Day of Month" bit.

I think part of the issue is that I keep confusing it as showing depth when it's just showing 'a thing happening'.

I'm not a geologist, but take some interest in this stuff only because I'm probably a bit nuts.

The RSAM trace shows overall seismic activity, SSAM shows a spectral analysis over that same time period.

Peaks in the RSAM chart may show an increase in overall seismic activity, volcanic tremor etc, the sharp peak lines are just quakes - which may be local and even volcanic, but probably not. A normal seismograph trace combined with location of the individual quakes from the seismograph network would show more, from the waveform of the tremor, it might be possible to determine if the quakes are tectonic rather than volcanic, short sharp "cracks" possibly from pressure from magma breaking rock, longer pulses possibly showing magma movement.

The SSAM charts are showing a spectral analysis, frequency of shaking movement from 0-20Hz on the scale on the left, intensity in dB shown by colour as per the scale on the right. Actually in some way AFAIK the way it's shown is a kind of proxy for depth, deep volcanic activity, magma movement will probably be lower frequency, as it rises the frequency of volcanic tremor will likely be higher.

But - most of what you see in the SSAM and RSAM at the moment on the charts is noise (possible exception IMO White Island). You can see a very clear trace on the Auckland charts showing vibration from traffic. On the Kermadec Island drums you can see the tides very clearly.

On the image below, you can see some weather (this is at Ngauruhoe), there's no big change in spectral pattern, it's just louder wind noise - except for those horizontal lines at about 10Hz and 14Hz which coincide with the weather patterns. I actually asked Geonet for confirmation and never got a reply - I think they're probably something on the equipment (like an aerial, or part of the instrument housing) that vibrate at those frequencies in the wind. There is a little bit of variation in very low frequency tremor that doesn't seem to correspond with anything, so there's probably something going on - it's an active volcano after all - but not much and there's no apparent trend.

I'd love for Geonet to join in and explain better. They do have a FB page - you could probably ask there too.

GV27

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#2022414 25-May-2018 12:48

Thanks for that Fred99.

The weather effects are pretty easy to pick out (Thunderstorms and wind really messes with the top part of the chart).

But I've always been miffed at how alert levels go up and yet the RSAM and SSAM looks to be business as usual. Obviously the factors behind the alerts are a multitude of things like gas emissions etc but I could never tell the difference between something and nothing.

Fred99

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#2031372 7-Jun-2018 12:13

GV27:

Thanks for that Fred99.

The weather effects are pretty easy to pick out (Thunderstorms and wind really messes with the top part of the chart).

But I've always been miffed at how alert levels go up and yet the RSAM and SSAM looks to be business as usual. Obviously the factors behind the alerts are a multitude of things like gas emissions etc but I could never tell the difference between something and nothing.

Here's something showing (Ruapehu):

An article here: https://www.geonet.org.nz/vabs/qvZnOZ70OccGmwoCkWqO6

You can see an increase in tremor in the RSAM and change in the SSAM, time corresponding to the observed increase in tremor and heating in the crater lake.
No - this doesn't mean it's about to erupt soon, it's within the range of normal variation / cycles observed in the past, they haven't changed the alert level.

Edit to say it also doesn't mean it won't erupt soon either - it's an active volcano, things can change fast.

GV27

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#2040838 20-Jun-2018 07:30

Fred99:

GV27:

Thanks for that Fred99.

The weather effects are pretty easy to pick out (Thunderstorms and wind really messes with the top part of the chart).

But I've always been miffed at how alert levels go up and yet the RSAM and SSAM looks to be business as usual. Obviously the factors behind the alerts are a multitude of things like gas emissions etc but I could never tell the difference between something and nothing.

Here's something showing (Ruapehu):

An article here: https://www.geonet.org.nz/vabs/qvZnOZ70OccGmwoCkWqO6

You can see an increase in tremor in the RSAM and change in the SSAM, time corresponding to the observed increase in tremor and heating in the crater lake.
No - this doesn't mean it's about to erupt soon, it's within the range of normal variation / cycles observed in the past, they haven't changed the alert level.

Edit to say it also doesn't mean it won't erupt soon either - it's an active volcano, things can change fast.

This has been interesting to watch - there was a quiet period up until recently, one long drawn out disturbance on the seismograph and then nothing again. I'll be curious to see the next update as there was going to be some sampling done at the crater at some stage, but it looks like it's quietening down again in line with the heating cycle.

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Fred99

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#2040891 20-Jun-2018 09:49

Yes - looks like it's settled back down to levels before the announcement of the "new heating cycle". There's no comment on this on the Geonet site, nor could I find anything on their FB page. OTOH it was "normal" variation in background, nothing more interesting seemed to happen, it does this regularly. Maybe they'll update the story to say what they found - maybe not.

This is a volcano story that's been in the news:

"There are no indications that Mt Taranaki is about to erupt, however, its unbroken geological history of activity tells us that it will in the future," the Taranaki CDEM website said. "We are in an unusually long (although not unprecedented) lull in activity. Recent research (2014) estimates an 81 per cent probability of at least one eruption by 2065."

https://cdemtaranaki.govt.nz/taranaki-hazards/natural-hazards/volcanic/

TBH, I'm a bit surprised that this is presented the way it has been, that's a very specific figure (81% / 47 years) and volcanoes are notoriously unpredictable. Even when they're in eruption and pre-eruption stage with activity being studied, for example with Mt Agung and Kīlauea events recently, the expert consensus seemed to be that "it might erupt or it might not, it might be big or it might not be, it might be like past eruptions or it might not, we know that this is happening (wrt magma movement observed, quake activity, deformation, gassing etc) but we don't know if this signals imminent eruption or not - let alone how serious the eruption may be". Meanwhile some other volcano that's not been in the news at all lets rip - kills people and creates chaos.

GV27

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#2041169 20-Jun-2018 15:20

That seems like a crazy high figure; higher than any one person witnessing an eruption in Auckland in the average lifetime, from memory.

Fred99

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#2041223 20-Jun-2018 16:24

GV27:

That seems like a crazy high figure; higher than any one person witnessing an eruption in Auckland in the average lifetime, from memory.

I agree it seems like a really high figure. I have no idea how it was calculated - ie whether they looked at historical activity intervals and extrapolated - or if they've got other data to suggest for example that a magma chamber is refilling based on seismological data and measuring ground inflation etc. I guess they're just using historical data.

Note that it's for "any" eruption, most are small, and they do say it's unlikely the next eruption will be a large one.

That said, it's a long time since NZ had a decent world-scale eruption, Tarawera (1886 - VEI 5 - probably a bit bigger than Mt St Helens) and since then not much of any real significance.

GV27

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#2042758 23-Jun-2018 10:40

Fred99:

I agree it seems like a really high figure. I have no idea how it was calculated - ie whether they looked at historical activity intervals and extrapolated - or if they've got other data to suggest for example that a magma chamber is refilling based on seismological data and measuring ground inflation etc. I guess they're just using historical data.

Note that it's for "any" eruption, most are small, and they do say it's unlikely the next eruption will be a large one.

That said, it's a long time since NZ had a decent world-scale eruption, Tarawera (1886 - VEI 5 - probably a bit bigger than Mt St Helens) and since then not much of any real significance.

Another piece:

https://www.stuff.co.nz/national/104926166/taranaki-probably-the-nz-volcano-most-at-risk-of-large-eruption-in-next-50-years

Makes it clear there's no evidence to suggest any activity at all at the moment; so I'm guessing the statistic above is just 100% based on historical intervals.

GV27

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#2063226 27-Jul-2018 06:28

Bumping my own thread

https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12095896

The goods:

They also unexpectedly found that the magma had been effectively triggered to erupt by a hotter batch arriving from deeper below.

And as the magma may have been sitting at depths of more than 50km for up to a year before the big blow, this suggested there could be eruptible magma present at any time.

Once the new hot magma arrived to destabilise the main body, the eruption took place between 10 and 30 days later – and more likely at the lower end of that range.

This is really cool. Reinforces the fact that Auckland is an active field; despite appearing docile, it could be primed and ready to go without us even knowing.

tdgeek

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#2063241 27-Jul-2018 07:13

GV27:

Bumping my own thread

https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=12095896

The goods:

They also unexpectedly found that the magma had been effectively triggered to erupt by a hotter batch arriving from deeper below.

And as the magma may have been sitting at depths of more than 50km for up to a year before the big blow, this suggested there could be eruptible magma present at any time.

Once the new hot magma arrived to destabilise the main body, the eruption took place between 10 and 30 days later – and more likely at the lower end of that range.

This is really cool. Reinforces the fact that Auckland is an active field; despite appearing docile, it could be primed and ready to go without us even knowing.

Fascinating

https://www.sciencelearn.org.nz/resources/1600-volcanoes-timeline

A few Googles shows the Auckland Volcanic field is young and active, and half of its history of eruptions has occured in the last 60,000 years, and getting more active.

Fred99

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#2063318 27-Jul-2018 09:09

IMO a disturbing factoid is that the last eruption (Rangitoto) ejected 60% of the magma that the field had ejected in multiple eruptions over 250,000 years. The eruptions seem to be getting bigger.

As they say in the Herald article: Another project was exploring how a large evacuation might unfold - something which posed a headache because of high uncertainty around location, styles, sequence and advance warning of any eruption.

So what would emergency authorities do in the scenario presented?

Magma intrusion detected at 27km depth - no history to show whether those magma intrusions happen frequently (in geological time) without an eruption, presumably without measuring ground inflation or whatever - which would probably only be possible when the magma had risen to shallower depth and it was about to blow, they'd be guessing how much magma had moved up so don't really know how big the eruption might be if it did erupt - nor where the eruption would be - but it could be in 5 days (or could be less). Causing panic isn't a great idea.

Evacuating 1/2 million people if you knew the location with 5 days warning is one thing, evacuating the entire population because you think something big is going to happen but don't know the location is another. A false alarm wouldn't be good - neither would trying to get 500,000 people evacuated in half a day when you did know roughly where the next volcano may appear.

GV27

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#2063320 27-Jul-2018 09:13

The 'eruption location' thing is a bit of a misnomer too; look at the vents spewing lava in Hawaii at the moment; some of those are 3km from the crater of the actual volcano.

It's possible you could end up with multiple significant evens in multiple places at once. You could have a cone in Mission Bay but lava all over the place in Glen Innes.

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