devongeography posted: " After watching irresponsible tourists getting themselves into difficulty at the edge of the lava flows from the new Geldingadalir eruption in Iceland, this article on the web took on a new significance. Can you outrun a lava flow? https://geoetc.com/l"
After watching irresponsible tourists getting themselves into difficulty at the edge of the lava flows from the new Geldingadalir eruption in Iceland, this article on the web took on a new significance.
Lava is often perceived to be the most dangerous hazard in a volcanic eruption, but it is hard to find a record of anyone actually being killed by a lava flow. Most people that lose their lives have been victims of volcanic gases, pyroclastic flows, lahars or tsunamis.
Image; NESA-US
So how fast does lava actually flow? Its speed is dependent on a number of factors:
The composition of the molten rock. Basaltic lava flows move much faster than rhyolitic lava flows. Also, the amount of gas dissolved in the lava can change the flows ability to flow (viscosity).
The rate of material that the vent is spewing out. During some eruptions vast amounts of lava are released and so the flows tend to be faster. Other eruptions only small amounts of lava are released, and so the flows are slower.
The slope of the land. A lava flow will move faster over steep slopes than shallow slopes.
If the lava is flowing in a sheet, a channel or a tube. When lava starts to flow it will move in a slow sheet. If the eruption continues, a channel might form along which the lava will flow faster. If that channel cools on its surface it can form a tube. Now the lava is completely contained and insulated. Lava can flow very fast inside the tube.
So, for example, a basaltic lava flow moving over a steep slope inside a lava tube will flow around 30 km/hr (19 miles/hr). On shallower slopes the flow will move less than 10km/hr (6 mile/hr) and most probably around 1 km/hr (thats like 1 foot a second).
Image: Science Friday
Yes – but can I outrun the lava flow?
The average adult human can walk at around 5 km/hr (3.1 miles/hr) and jog at around 11 km/hr (7 miles/hr). In short bursts humans can run at 32 km/hr (20 miles/hr).
So people could easily walk, jog or run away from almost all lava flows….unless they are in an unusual situation such as a steep sided very narrow valley leading to a volcanic event that is churning out basaltic lava at a huge rate. That situation is particularly rare.
REYKJANES PENINSULA, ICELAND - MARCH 25: Hikers look at lava flows from the erupting Fagradalsfjall volcano in Geldingadalur on March 25, 2021 in Reykjanes Peninsula, Iceland. On March 19 the Icelandic meteorological office announced a volcano, referring to a mountain located south-west of the Capital Reykjavik has erupted after thousands of small earthquakes in the area over the recent weeks. This was the first eruption on the Reykjanes Peninsula in approximately 800 years. (Photo by Matthew Eisman/Getty Images)
Nevertheless, there is no accounting for people's stupidity at times. Some people endanger themselves (and others) by getting too close to accessible lava flows. The problem is then not running away, but losing your footing and falling in. The tourists in Iceland recently created problems when they failed to notice the lava flowing around them, and cutting them off from their exit route – a bit like getting caught out on a beach with a rising tide.
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