Underwater Volcanics

 volcanoes  Comments Off
Nov 192011
 
Monsal 2

With the current interest in El Hierro, the island in the Canaries that is currently experiencing an underwater volcanic eruption, I thought I would post some images from the eruption of volcanic lava into the sea some 330 million years ago. In the picture below, the lava is entering from the right with the background sedimentation of the Carboniferous Monsal Limestones seen to the left.

This is the site near Litton in Derbyshire where the Upper Miller’s Dale lava entered the Lower Carboniferous epicontinental sea. The resulting rock is a hyaloclastite. The basaltic lava entering the sea water produces thermal shock and stream explosions that fracture the rock.

This section is on the Monsal Trail, a former railway line that has been converted into a walking/cycle trail. The tunnels, which until recently were bricked up, are now paved, lit and open allowing easy access to some really nice exposures. By the entrance to Litton Tunnel is further evidence of Lower Carboniferous volcanic activity with a bentonite ash layer (yellow, on right).

Geology Errors on Children's BBC Website

 BBC, volcanoes  2 Responses »
May 252007
 

I’ve just come across a page on the BBC Children’s website ‘explaining’ volcanoes [What causes volcanoes?] and it is full of basic errors of geology. If the BBC can’t get simple facts right for children what hope do we have in creating a proper understanding of our planet and our subject. I appreciate that they have to keep things simple for children but that is no excuse for fundamental errors of fact!

To Fisk the article …
Inside the earth’s core there is a red-hot liquid rock, called magma.

The Earth’s core has absolutely nothing to do with volcanoes. It is the Earth’s crust that has magma inside it – the core is 2900km away!

Note also that it is “Earth’s” – it is a formal name of a planet, earth is soil.

Volcanoes happen when magma rises to the surface of the earth, which causes bubbles of gas to appear in it. This gas can cause pressure to build up in the mountain, and it eventually explodes. When the magma bursts out of the earth, it is called lava.

This is not true of all volcanoes (and certainly not true of Hawaii which was the subject of the story to which this page linked). Also the gas bubbles won’t usually appear in the magma until the pressure is released and the eruption starts.

In a survey of school geology textbooks the factual error rate was found to be at least one per page! The producers of so called scientific content really do need to check their facts properly and the BBC should do much better.