Posts Tagged ‘Grímsvötn’

Computer models are only models – and subject to common sense

May 25, 2011

Once again the blind belief in computer models has closed down parts of European air space. Observations and measurements are given less weight than computer models which are at best crude approximations of a chaotic system. The unthinking belief in approximations to reality merely because they are generated by computer models denies the sapience in homo sapiens!!

BBC:

Most flights have resumed across the UK after a day that saw thousands of passengers affected by an ash cloud from the erupting Icelandic volcano. Air traffic control company Nats said harmful concentrations of ash dispersed from UK airspace overnight. But some flights within the UK and a number to Germany will be cancelled.

As one blogger puts it:

Airline managers are complaining that last year, officials did not do enough to check the actual conditions in the air, instead relying too heavily on computer models showing where the ash was supposed to be. Yet, despite the experience, the International Air Transport Association (IATA) is saying that it is “astonishing and unacceptable” that a British aircraft that is supposed to check actual conditions has been unable to fly.

The disruption arises in part from “volatile winds” which are said to be carrying clouds of volcanic ash down from Iceland over the northern British Isles. But those same winds which caused the rough weather yesterday must also have dispersed the ash.

Without real data, however, forecasters are unable to provide accurate information on ash density and particle size, relying instead on weather patterns and computer modelling to give a rough approximation of conditions. And, with no clear guidance as to closure rules, the only significant difference between this year and last is that the weather conditions are more changeable, allowing more favourable estimates of ash dispersion to be made.


Climate Realists: We know that the Met Office doesn’t bother much with evidence, witness Prof John Mitchell’s unguarded remarks at the Downing College Conference:

People underestimate the power of models. Observational evidence is not very useful,… Our approach is not entirely empirical.

Iceland volcano watch stands down

November 6, 2010

Jökulhlaup from Grímsvötn subsides

The earlier concern about meltwater flooding from the Grimsvotn glacial lake in Iceland which could have signalled that the volcano underneath was about to erupt has subsided.

Bridge over Gígjukvísl

Figure 1. The jökulhlaup from Grímsvötn: image vedur.is

The jökulhlaup (glacial outburst flood) from Grímsvötn that began near the end of October is now coming to an end. The flood reached a maximum level shortly after noon on November 3, and scientists from IMO visited the site on that day to study the effects of the flood on the region adjacent to the ice margin. Two IMO technicians have performed regular discharge measurements on the bridge over the river Gígjukvísl throughout this week (Figure 1) and the results from their measurements are shown in Figure 2.

Figure 2. Discharge (m3/s) measurements at Gígjukvísl bridge: From the curve the total amount of floodwater is estimated 0.45 km3

The discharge curve is typical for jökulhlaups from Grímsvötn that do not result from volcanic activity: Over the course of several days, the amount of water flowing through an ice tunnel at the glacier bed steadily increases. Loss of frictional heat from the floodwater causes melting of the tunnel walls, thereby increasing the flow capacity of the tunnel.

In past centuries, most jökulhlaups from Grímsvötn have entered the course of the river Skeiðará. This time, however, floodwater that emerged from beneath the eastern part of the glacier went westwards along the glacier margin and then entered the river Gígjukvísl. Skeiðará has deposited very large amounts of sediment on the eastern part of Skeiðarársandur plains over the centuries, increasing the elevation of the sandur area there relative to the central part. In addition, the glacier has carved a trench during times of advance. Thus, it was clear that retreat of the glacier over the past 15 years would sooner or later lead to a drastic shift in the direction of meltwater flow from this part of the glacier. In the summer of 2009, this shift occurred and water has ceased to enter the course of Skeiðará.

 

Iceland on watch for new volcano eruption

November 1, 2010

Reuters:

Meltwater is flooding from the Grimsvotn glacial lake in Iceland and could signal the volcano underneath is about to erupt, a spokeswoman at the Icelandic Civil Protection Department told Reuters on Monday.

Water now pouring from Iceland’s biggest glacier, Vatnajokull, which sits on top of a number of volcanic hotspots, could be a sign of fresh geological activity, Civil Protection Department spokeswoman Gudrun Johannesdottir told Reuters.

In April, clouds of ash from an eruption under the Eyjafjallajokull glacier grounded flights across Europe for a week, causing billions of dollars in losses for airlines and other industries. Eyjafjallajokull is about 100 km southeast of Vatnajokull.

“We have to check if there will be an eruption,” Johannesdottir said. “Sometimes it initiates an eruption when a glacial outburst flood starts, but not every the time. So we are monitoring the situation closely.”

The latest eruption at Grimsvotn, in 2004, caused short-term disruptions to airline traffic into Iceland.

 

Smoke from a subglacial volcanic eruption rises above the Vatnajökull ice cap (file photo by Oddur Sigurdsson)

 

 


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