Separe os nomes com vírgulas.
Tópico em 'Sismologia e Vulcanismo' iniciado por luismeteo3 7 Jan 2018 às 15:22.
Espetáculo... Do mesmo vulcão mencionado aqui pelo @luismeteo3 recentemente
Turrialba and Rincon de la Vieja Volcanoes in Costa Rica Are Very Active
Turrialba Volcano Photo of Eruption Registered November 2. Archive
This Sunday, November 4th two of Costa Rica’s volcanoes registered important activity; the Turrialba Volcano in Cartago presented an eruption with an ash column that reached 500 meters above the crater or 3,484 meters above sea level (12595.2 ft).
In Guanacaste, the Rincon de la Vieja volcano began its activity at 7:45 p.m., the weather conditions at the time of the eruption didn’t allow to confirm the height reached by the column; the activity lasted for close to 12 minutes with an eruptive sequence of at least three episodes of two minutes each, the nearby community reported smell of Sulphur.
The Turrialba volcano has registered several eruptions since the beginning of October, prior to the activity this Sunday it also had important activity on November 2; while the Rincon de la Vieja registered its last short eruption back on October 17.
Autoridades da Guatemala ordenam evacuação de áreas próximas do vulcão de Fogo
19.11.2018 às 8h38
JOHAN ORDONEZ/GETTY IMAGES
O vulcão, de 3.763 metros de altura, situa-se nas regiões de Escuintla, Chimaltenango e Sacatepéquez, a 50 quilómetros a oeste da capital da Guatemala
As autoridades da Guatemala ordenaram esta segunda-feira a retirada da população de pelo menos oito comunidades do país, devido à quinta erupção do vulcão de Fogo este ano.
O vulcão, de 3.763 metros de altura, situa-se nas regiões de Escuintla, Chimaltenango e Sacatepéquez, a 50 quilómetros a oeste da capital da Guatemala.
O porta-voz do Coordenador Nacional para Redução de Desastres, David de Leon, disse que a população de pelo menos oito comunidades deve retirar-se e procurar estabelecer-se em áreas mais seguras.
A 3 de junho, o vulcão de Fogo registou uma das erupções mais fortes da sua história, afetando quase dois milhões de pessoas. De acordo com o último balanço das autoridades, pelo menos 194 pessoas morreram e outras centenas ainda estão desaparecidas.
Este pequeno país da América central situa-se no “anel de fogo do Pacífico”, uma zona que concentra cerca de 90% da atividade sísmica terrestre.
Enviado do meu iPhone usando o Tapatalk
Hekla – Small things and stars in the night
Carl / 22 hours ago
Hekla during the 1980 eruption. Photograph by Oxonhutch, Wikimedia Commons.
I was asked to write a small weekend piece while we wait for Albert to finish the second part about Grimsvötn. My original idea was to write about people eating volcanoes, but thankfully Iceland saved us from that.
As many of you have noticed Grimsvötn has thrown some big ones since my part of the two-part article, but I know that Albert is diligently working those ones into his article, so I will leave out Grimsvötn being hard at work to meet that 31st December 23.59.59 o’clock deadline to outshine the Reykjavik fireworks.
Stars in the night. Image by the Icelandic Met Office.
Iceland is most likely the only place on earth that will cause people to look down towards the ground if you say, “Oh, look at the stars”.
As many of you know a “star” is an earthquake above M3 on the Icelandic Met Office earthquake page. As I write this there are 3 stars in Iceland at Bláfjallaskal, Grimsvötn and Hamarinn. And as we all know, big earthquakes in volcanoes can be signs that things are about to go down.
Problem is that Hamarinn can throw these now and then without any impending doom, and the same goes for the tectonically active part of Iceland that houses Bláfjallaskal. So, if big things are not necessarily a sign of big eruptions, where do we look?
Sideways plot showing the earthquakes of Hekla. Image by Andrej Fliis using data from the Icelandic Met Office.
The last 24 hours are among the most interesting and downright intriguing in volcanological history, and that is even counting eruptions like Cerro Hudson, Holuhraun and Pinatubo. The air was filled with the brimstone smell of heavy science data collection being done in the dark.
Before and during the 2000 eruption of Hekla the monitoring network was not bad for its time but compared to today it was a kayak crossing a small lake compared to a rocket hurling a Tesla playing David Bowie towards Mars.
Not only have we gotten more seismometers, GPS-stations, strain meters and a new funky multigas-measuring station. All of the old equipment has been replaced with new and far more sensitive instruments.
Basically, what will trigger the automatic system today would be hard to manually find back then. Today the automatic threshold is a staggering -1.2 on the moment magnitude scale. And it is possible to manually see earthquakes that are even smaller.
Possible location of deep conduit, upper magma reservoir and vent conduit. Image by Andrej Fliis using data from the Icelandic Met Office.
The same level of upgrades is also there for the GPS and the strain meters. And we have the gas station on top of the mountain and an infra-sound detector down at Katla.
Yes, there are more pieces of equipment on a couple of volcanoes, but nowhere on earth is the average density versus quality higher.
I am mentioning this for two reasons. One is so that you will understand that there are more earthquakes picked up now than during the last eruption. And the second reason is that we can now be almost certain that we will be able to pick up the pre-eruption signs of Hekla.
This is my prefered interpration where we see a wedge shaped magma reservoir with earthquakes indicating pressure release zones and/or vertical sills. Image by Andrej Fliis using data from the Icelandic Met Office.
Obviously, we are not entirely sure what those signs are, since we have never seen them before, but we can make educated guesses. And, we can also compare it to the 2000 eruption signs that we did pick up and extrapolate from there.
Only problem is that apparently Hekla is throwing us a Black Swan moment. Because according to our known extrapolations and guesstimates Hekla started an eruption this morning. At least if we go with the seismometer network data.
2018 earthquake activity showing well the location of the current activity. Image by Andrej Fliis using data from the Icelandic Met Office.
So, where is the brimstone and fiery doom that our beloved Hekla is famous for? I will now try to answer that question.
In 2011 all seismic network upgrades except station HES was in place. From that moment the data quality does not increase a lot and we can safely say that there is no large technology skew increasing the numbers of earthquakes. Well, except in the direction of HES obviously, and that HES gave us better depth resolution.
The 2013 Hekla Seismic Crisis
IMO earthquake page showing the earthquakes that caused this article. Image by the Icelandic Met Office.
In 2013 Hekla threw up it’s most numerous post eruptive earthquake swarm. At the time it was assumed that Hekla would erupt, and even the Icelandic Met Office put up a bulletin that an eruption at Hekla was imminent. I was also fooled by Hekla and thought it would go off.
In the end no eruption occurred but post the seismic crisis that has been the benchmark of what the maximum unrest Hekla could withstand without an eruption following.
I had a bit of a problem with that idea. The location of those earthquakes was not in line with what had been observed prior to Hekla’s last eruption in 2000.
Hekla seismic trend plot. Notice the difference in M0.8 earthquake count between this month and 2013. Image by the Icelandic Met Office.
In 2000 against what most people believe there was a small swarm about two weeks prior to the onset of eruption. That small swarm occurred slightly west of the southern terminus of the Heklugjá fissure swarm.
It is normally said that Heklugjá is 7 kilometres long and that it runs the length of the actual mountain. But that is the top of the fissure that normally opens during an eruption, the fissure at depth is a bit longer. Perhaps 3 km to the NNE, and some 7 to 10 kilometres further SSW. This is very clear on the plots that Andrej has made for this article.
The pre-eruption swarm in 2000 is a logical place swarming for a fissure system under intense magmatic pressure, because the pressure will attack the weakest points to make room for that magma.
Earthquake trend plot for Hekla of all data. Please notice the increase as the big upgrades of the system came online. Image by Andrej Fliis using data from the Icelandic Met Office.
The NNE end is fairly blocked off due to the neighbouring Torfajökull volcano, and the Vonarskard and Veidivötn fissure swarms taking care of the business Icelandic continental spreading.
That means that the best spot to grow is the SSW end, and this is evidenced by that part being considerably longer than the NNE part.
In 2000 the ever-increasing magma pressure tried to make more room at the southern end causing pressure induced earthquakes there. In the end that did not work well enough, and the pressure after a while attacked another weak spot, the topmost part of Heklugjá that runs the length of the edifice known as Hekla proper.
No such thing was seen in 2013, so in hindsight the obvious conclusion is that the pressure was not high enough for the earthquakes to be part of a pre-eruptive sequence.
Earthquake versus depth plot over time. Image by Andrej Fliis using data from the Icelandic Met Office.
If the relatively small earthquake crisis in 2013 can be called a seismic crisis what we are seeing now is more like seismageddon (in a piddly Hekla way). Just to put it into perspective, the total earthquake count now is 3 times larger, and the amount of earthquakes per month above M0.8 is by now twice the number.
So, just on pure numbers this has transcended 2013. But that is not the point that is important. The important thing is the location.
This time a large percentage of the seismic activity is slightly west of the southern terminus of Heklugjá indicating intense pressure. The earthquakes are though small, the same as in 2000.
Since the network now is far more sensitive than in 2000, we are seeing quite a few more small earthquakes. That is why the IMO is using the M0.8 and upwards as the divider for their master plot. A M0.8 earthquake was easy to detect in 2000, and none of those would have been missed even at the old network, so this makes it easy and accurate to compare with now.
All things taken together, we know that the GPS-system says that the pressure levels by now are higher than they where back before the 2000 eruption, we are seeing magma system pressure earthquakes at the correct location, but we are not seeing any untoward twitching on the strain meters.
So basically, we have 2 out of 3 of the prerequisites known for an upcoming Hekla eruption. And the strain twitching normally starts just a few minutes prior to onset of eruption.
I will not say that Hekla will erupt soon. Suffice it to say that there are far more signs of an eruption being on the way now compared to 2013.
It has been an interesting and exhausting 24 hours, and even if there will not be an eruption this time around, Hekla gave us all a true masterclass in volcanology, and for that we will have to be thankful.
Já que uma erupção no vulcão Hekla parece estar relativamente próxima, deixo aqui um video para reavivar a memória...
Monitorização do vulcão Hekla live: http://volcanocafe.net/brennstein/g...V4_4mvNT6vxNp4Fl0WOkhvjX0Z2z1vK7D-0cJQrq97TKE
Short-Term Seismic Precursors to Icelandic Eruptions 1973–2014
Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland
Networks of seismographs of high sensitivity have been in use in the vicinity of active volcanoes in Iceland since 1973. During this time, 21 confirmed eruptions have occurred and several intrusions where magma did not reach the surface. All these events have been accompanied by characteristic seismic activity. Long-term precursory activity is characterized by low-level, persistent seismicity (months-years), clustered around an inflating magma body. Whether or not a magma accumulation is accompanied by seismicity depends on the tectonic setting, interplate or intraplate, the depth of magma accumulation, the previous history and the state of stress. All eruptions during the time of observation had a detectable short-term seismic precursor marking the time of dike propagation toward the surface. The precursor times varied between 15 min and 13 days. In half of the cases the precursor time was <2 h. Three eruptions stand out for their unusually long duration of the immediate seismic precursory activity, Heimaey 1973 with 30 h, Gjálp 1996 with 34 h, and Bárðarbunga 2014 with 13 days. In the case of Heimaey the long time is most likely the consequence of the great depth of the magma source, 15–25 km. The Gjálp eruption had a prelude that was unusual in many respects. The long propagation time may have resulted from a complicated triggering scenario involving more than one magma chamber. The Bárðarbunga eruption at Holuhraun issued from the distal end of a dike that took 13 days to propagate laterally for 48 km before it opened to the surface. Out of the 21 detected precursors 14 were noticed soon enough to lead to a public warning of the coming eruption. In four additional cases the precursory signal was noticed before the eruption was seen. In only three cases was the eruption seen or detected before the seismic precursor was verified. In general, eruptions are preceded by identifyable short-term seismic precursors that, under favorable conditions, may be used for pre-eruption warnings. In some cases, however, the time may be too short to be useful. The Hekla volcano stands out for its short precursory times.