If you remember, last November, TVJ (with the aid of Malcolm and his photos) gave us a very interesting talk on zeolite minerals. These minerals are to be found in ancient lavas that flowed out millions of years ago from volcanoes such as those at the Etendeka Plateau in Namibia or the Deccan Trappes in India. Later such minerals as analcime, chabazite, heulandite, and apophyllite were created by mineral rich solutions percolating through the porous rock and filling the residual cavities, known as amygdales.

To learn more about the story before the formation of the minerals though, we need to do some volcanic research. The Etendeka Plateau and the Deccan Trappes were formed by massive outpourings of lava from volcanoes whose eruptions lasted for thousands of years. These eruptions filled the skies with sulphurous gases which caused havoc with life on Earth, robbing it of oxygen and sunlight, poisoning the air and causing temperatures to drop for a considerable length of time. The Deccan events are now considered one of the main reasons that the dinosaurs died out, as well as much other animal and plant life on Earth during that period. The Deccan Trappes volcanoes began erupting 66 million years ago and were so incredibly powerful that they left nearly 200,000 square miles (518,000 sq. km) of what is now India buried in volcanic basalt up to a mile and a half thick. The Etendeka volcanic field is even older with an age of 132 million years. This series of eruptions is related to the opening of the South Atlantic Ocean which forced the two continents apart when Gondwana broke up. At that time Namibia was still attached to the Parana volcanic field of Brazil and their combined extruded volume is estimated to have covered some 1.3 million cubic kilometres both on land and under the newly created sea. The far more recent Krakatoa eruption of 1883 “only” spread volcanic ash for about 18 km.

At least events like those don’t happen nowadays, you may say, but are you sure? For the avid follower of volcanoes and the associated topic of the movement of tectonic plates, there is an almost daily source of interest. The most recent Bardabunga event in Iceland is no longer in the newspapers, but that doesn’t mean to say it is no longer active. The actual lava flow maybe slowing down a little, but overall, since it started erupting in August 2014, it has spread over more than 84 square kilometres (32 square miles) of Iceland – an area larger than the island of Manhattan. This Holuhraun field is Iceland’s largest basaltic lava flow since the Laki eruption in 1783–84, an event that killed 20 percent of the island’s population. At its height the Bardabunga caldera emitted so much sulphur dioxide that downwind it caused breathing problems in the local community, and there was also concern that there would again be as much ash as had disrupted air traffic during the Eyjafjallajökull eruption of 2010.  You could say that it was fortunate that this was a steady outflow of lava from a hot spot (or mantle plume) from a deep fissure in the Earth and not an almighty eruption like Mount St Helens in 1980 that destroyed more than half the mountain in its main blast.   (http://pubs.usgs.gov/fs/2000/fs036-00/)

In East Africa’s Rift Valley, there is a string of volcanoes all along its length, where a part of the continent is very slowly but steadily breaking away from the main plate. It is thought that possibly this severing was caused by a series of hot spots breaking through the existing continent. Two of these volcanoes, Nyiragongo (Democratic Republic of Congo) and its neighbour Nyamuragira, are currently rated in the top four hottest volcanoes of the World.  (STOP PRESS – 14 FEB 2015 - Plumes From Africa’s Volcanic Duo.  http://earthobservatory.nasa.gov/IOTD/view.php?id=85273&src=eoa-iotd  )

Recently in Hawaii, houses and farmlands have been swallowed by the creeping lava of the latest Kilauea eruption on the northeast flank of Puu Oo, which has been flowing again since July last year. Locals tried building earth walls and dug ditches, but nothing would stop the steady and relentless flow of the lava as it moved towards the town of Pahoa burying fertile fields and farmhouses in its path. Sometimes, in places like Hawaii, a new island forms at the end of the island chain. Why at the end of the chain and not an eruption that reoccurs on an existing island? This is because even though the volcanic hot spot stays in the same place, the continental plate is steadily moving across it, and when the need for the next eruption occurs, the plate has moved and the lava must now force itself up through a new part of the Earth’s crust and then the sea bed, and so a completely new island is formed. This is known as a sea mount. Loihi is currently such a volcano, located about 35 km off the southeast coast of the island of Hawaii and about 975 m (3,000 feet) below Hawaii. Unlike most active volcanoes in the Pacific Ocean that make up the active plate margins on the Pacific Ring of Fire, Loihi and the other volcanoes of the Hawaiian chain are different, and known as a hot spot volcanoes. These are upwellings of lava from the mantle which form well away from the nearest plate boundary.

In America, Yellowstone Park’s caldera is also a hot spot or mantle plume volcano that first erupted about 640,000 years ago. It now covers an area of about 30 by 45 miles. The last major eruption was about 174,000 years ago, and the last lava flow about 70,000. At the moment it is considered unlikely to erupt in the near future even though it continues to rumble away with continuous minor earthquakes, and releases heat via hot water geysers. The area is constantly monitored for unusual subterranean activity, which would indicate a change in its status. Nothing could be done to prevent an eruption though.

Japan is also a string of volcanic islands, but these are found on the edge of a tectonic plate. On 27th September last year Mount Ontake erupted without warning killing fifty seven people. Climbers and tourists were still standing on the mountain when it erupted, and later photographs were found in abandoned cameras showing the recent activities of the deceased near the summit right up until the time of the explosion.

When I had almost finished writing this article, it became apparent that even for a layman, following the activity of volcanoes can become a complete fascination. I hadn’t realised just how many volcanoes I had tracked in the past year, and they are linked to earthquakes, tsunamis, and more. Tracking volcanic activity is most definitely a never-ending story; so if you too are interested, here are a few pointers to follow:

Sources of information:

-          The Story of Earth and Life by Terence McCarthy & Bruce Rubidge and published by Struik is an excellent reference book and is available in the Club’s library.

-          The weekly NASA email newsletters that one can subscribe to for free, give up to the minute reports on what their satellites have located recently. Almost every week there is a report of a new volcanic eruption somewhere.


-          U.S. Geological Survey http://volcanoes.usgs.gov/yvo/monitoring.html  http://hvo.wr.usgs.gov/activity/kilaueastatus.php

Likewise, there are certain dedicated volcano following sites:




Jo Wicht