Tag: volcanic rock

australasia geology volcanoes

Geo junkets: New Zealand, North Island (Part 1)

Jesse Garnet White (USA) Fig. 1. Legend/Key:1 = Sediments (Cretaceous and Cenozoic).2 = Greywacke (Permian and Triassic).3 = Schist (Carboniferous to Cretaceous).4 = Volcanic rocks (Cretaceous and Cenozoic).5 = Sediments and ophiolites (Northland and East Coast allochthon) (Cretaceous and Oligocene).6 = Pyroclastic rocks (Triassic and Jurassic).7 = Limestone, clastics and volcanic rocks (Central and Eastern sedimentary zone) (Cambrian to Devonian).8 = Granitoids (Paleozoic and Cretaceous).9 = West Fiordland metamorphic zone (Paleozoic and Cretaceous).10 = Ophiolites and pyroclastics (Permian).11 = Volcanic rocks (including pyroclastics) (Permian).12 = Mafic and ultramafic complexes (Paleozoic and Cretaceous).13 = Greywacke (Western sedimentary zone) (Cambrian to Ordovician). Auckland and the AVF In a thick brain fog, crusty eyed and yawning, I sat up in bed at 4:30 am. I was in Auckland, New Zealand. It was still dark outside when I drove to Mount Eden (Maungawhau), where I hiked up a narrow dirt trail lined by tall grass stippled with dew. Coming out of the verdure, my shoes, socks and shorts were soaked through. On top of the hill, a shadow-black grouping of trees blocked the creeping morning light from behind the Hanua Ranges. The burnt orange sunrise, obstructed by cumulous, lit up like a distant mountain wildfire. Auckland city centre was under puffy, lavender-white cirrus clouds, reflecting pastel colours across the harbour. Alone in the cool and crisp pre-dawn air, I viewed the various scoria cones in the Auckland Volcanic Field (AVF) bursting through the city neighbourhoods. Fig. 2. Map of New Zealand showing place names. … Read More

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europe geology historical / biographies urban, art, anthropology volcanoes

Volcanism in the ancient world

Dr Robert Sturm (Austria) In the ancient Greek and Roman world, volcanism was recognised as a divine phenomenon standing in close connection with the fire god, Hephaestus or Vulcan. Although there did not exist any term corresponding to the modern word “volcano”, people were aware of the destructive power arising from volcanic eruptions. Some early natural philosophers were already able to identify individual volcanic processes, such as lava flow and the generation of huge and extremely hot dust clouds. In the ancient Greek language, lava masses streaming downhill were simply named “rhea” (ῥύαξ or flow), whereas the Latin words “Vulcanius amnis” (Vulcanic stream), “saxa liquefacta” (liquefied rocks) and “massa ardens” (blazing mass) were used for the same phenomenon. Volcanoes were of enormous importance for the ancient Mediterranean world, because their eruptions caused the destruction of adjacent settlements and even the annihilation of entire civilizations. According to our present historical and archaeological knowledge, three volcanoes had an immense influence on the development of Mediterranean cultures: (1) the volcano of Thira-Santorini, which left behind the huge caldera visible today; (2) Vesuvius near the city of Naples; and (3) Etna on the island of Sicily (Fig. 1). Fig. 1. A satellite map of the Mediterranean region, including the position of the three volcanoes covered in this article. Despite the Thira-Santorini volcano being situated in the Aegean Sea, Vesuvius near Naples and Etna on Sicily, they are all considered to be part of the western Mediterranean Sea. (Photo: ©NASA.) In this article, I intend … Read More

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africa / middle east geology minerals urban, art, anthropology volcanoes

La Gomera: A short geological guide

Ken Madrell (UK) The island of La Gomera has an area of 370km2, it is 25km in diameter, has a maximum altitude of 1,487m (Alto Garajonay) and is situated approximately 40km west of Tenerife. Unlike the other Canary Islands, La Gomera has experienced a long and continuing eruptive break and is in a ‘postshield erosional stage’. Carracedo and Troll (2016) describe this as the stage when active volcanism has ceased, and erosive and denudational landforms are predominant (p. 39). The submarine base of the island shows that it rests on a shallower ocean bed than the surrounding islands. The emerged land mass is semi-circular in shape, with a radial drainage pattern from its centre near Alto de Garajonay. The dating of the island has proved problematic, as some of the earlier measurements placing its age between 15 Ma and 19 Ma have since proved to be inaccurate. More reliable estimates now put its age at between 10 and 11 Ma. Fig. 1. Roque Argando viewed from Lomo de la Mulata. La Gomera’s general stratigraphy comprises of three main rock sequences: (1) A Miocene basaltic shield, including a basal plutonic complex (that is igneous rock formed by solidification at considerable depth beneath the earth’s surface); (2) A nested felsic (that is, igneous rocks that are relatively rich in elements that form feldspar and quartz) stratovolcano (which is built up of alternating layers of lava and ash); and (3) The youngest Pliocene volcanism. Fig. 2. Sketch map of La Gomera, showing the … Read More

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geology minerals north america volcanoes

Volancoes of Big Island, Hawaii (Part 3)

Dr Trevor Watts (UK) This is the last of a three part article about the volcanoes of Big Island, Hawaii. In the first part, I discussed their background and explained some of the terms used to describe the lava that can been seen there. In the second, I discussed some of the highlights that my wife and I saw during our several trips to the island, including in October 2014. And in this part, I will continue to describe what we saw. Fig. 1. One of the kipukas (that is, untouchedby- lava areas of forest). The abandoned lava cliff at Kalapana This is a stretch of old cliff face that is now several hundred metres from the sea. It is located among the flows of February 1992 to October 2003, but the area was re-flooded with lava between 2007 and November 2013, when the ocean entry hereabouts was blocked. The site is just under 5km southwest of present-day Kalapana near Poupou, where the Royal Gardens lava flow reached the coast. The walk is well worth the effort for the variety of lava formations, the many tumuli or blisters of lava, and the coastal scenery along the present cliffs. We were guided here by Gary Sleik, who lives on the lava at Kalapana. Fig. 2. The first section of cliff face, with the lens-shaped tube blocked by cindery flow. The cliffs are backed up by a small kipuka, which is an area that was left untouched, as the lava flowed around … Read More

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england fossils geology minerals palaeontology

What’s so special about South Devon?

Professor John CW Cope (National Museum of Wales, Cardiff UK) Take a trip to the South Devon coast around Easter time and you are bound to come across student parties from universities engaged in fieldwork. What is it about this area that makes it so popular as a centre for this? The simple answer lies in a single word — variety. There is probably no other area in the UK where such a wide variety of rock types and ages is well-exposed in such a small geographical compass. Let’s have a look at some of the factors. The geological succession The oldest rocks exposed in South Devon are of Devonian age and, unlike many other areas of the UK, the Devonian rocks are in marine facies virtually throughout. Looking back over the history of geology, the age of these rocks had initially proved difficult to identify and it was only after Murchison had seen the marine successions in The Rhineland and Russia that he realised that these marine rocks were the equivalent of the Old Red Sandstone farther to the north. The Devonian rocks present a variety of marine facies, with the Middle Devonian limestones being of particular note. The limestones are a local development whose presence, in an otherwise deeper water succession, is due entirely to local shallowing of the water caused by thicknesses of volcanic rocks extruded along extensional fault lines as the local basins developed. This shallowing allowed reef-building organisms to flourish and the principal ones of … Read More

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geology minerals northern ireland volcanoes

Giant’s Causeway (Part 2): Other volcanic highlights

Dr Trevor Watts (UK) This is the second and final part of an article on the volcanic highlights of Northern Ireland’s Giant’s Causeway and surrounds. For the first part, see Giant’s Causeway (Part 1): An introduction.) We were in the area for several days and the weather was fairly mixed, but there were glorious skies between the showers, and the high winds brought the waves up beautifully. Of the six highlights discussed below, we visited the first three in one day, as all were a few kilometres to the west of The Giant’s Causeway. Those to the east, we visited on another day. Fig. 1. A map of some of the highlights. They are all supremely interesting and give an idea of the range of volcanic features to be seen. You cannot see an actual, traditional volcano in Antrim, with its classic shape. However, you can visit many scattered and varied elements of the area’s vulcanicity, and so gain an appreciation of the overall picture. Fig. 2. Fanciful cross section of highlights. 1. Deep lava flows forming the Causeway Basalts and their columnar basalt features. Found at The Giant’s Causeway and Ballintoy Harbour. 2. Beds of red ‘laterite’ rocks and soils buried by the later lava flows. Seen along the whole coast, especially east of the Giant’s Causeway. 3. Multiple relatively thin lava flows forming the Lower Basaltic Series. Seen at The Giant’s Causeway area and Dunluce Castle. 4. Dykes bringing magma towards the surface through fissures of cracks in … Read More

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palaeontology

Jamaica’s geodiversity (Part 1): Introduction and some older highlights (Cretaceous to Miocene)

Stephen K Donovan (The Netherlands) and Trevor A Jackson (Trinidad) With a length of only about 240km, Jamaica cannot be considered a large island. It is also relatively ‘young’ geologically, the oldest rocks being only about 140myrs old. This might sound old enough, but contrast it with, for example, rocks in the islands of the Scottish Outer Hebrides, which are about 2,000myrs old. But Jamaica is nevertheless noteworthy in having a rich diversity of rock types and geological features, and it is rightly known for its high biodiversity, both on land and in the surrounding seas. To give one example, the 500 or more species of extant land snails make Jamaica a biodiversity ‘hot spot’ for these familiar molluscs. However, Jamaica should similarly be recognised as a geodiversity hot spot, with a range of geological and physiographic features, strata and fossils that make it an unusually fruitful focus for earth sciences research. We could support our bold assertion by a detailed exposition with tabulation of principal features and comparison with similar-sized islands elsewhere, although such an approach would perhaps be better suited to a dry research journal. The potential for producing such a long, boring discursion is large and we intend to avoid the temptation to do so. Rather, we want to illustrate Jamaica’s geodiversity by reference to a dozen key features. These are available for inspection to anyone who is interested and which we will describe in two articles in Deposits. The choice of these features is personal – … Read More

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africa / middle east volcanoes

Pico Partido: Volcanic perfection in the Canaries

Dr Trevor Watts (UK) Lanzarote is the easternmost island of the Canaries, less than 100 miles (about 150km) off the coast of Morocco. It is part of Spain, but not officially in the European Union and Pico Partido is a sharp, prominent peak near the centre of the island, between the small town of Mancha Blanca and the volcano of Timanfaya. The name means “divided mountain”, so called because the high peak is split by a deep fissure that seems to chop it in two. And it is enthralling. It is a basket of volcanic jewels to be treasured, particularly after the disappointment of the lack of access to Timanfaya itself (of which, more later). And Pico Partido is accessible, unlike much of the island where too many roads have no lay-bys or even a patch of cinder where you can pull in and explore. The geology of Lanzarote Lanzarote, with its volcanoes, is sitting on the tectonic plate that forms most of Africa. It is not near the edge, so it is not formed by one plate sinking under the other. Nor is it above a rising mass of magma, a hot spot. A little surprisingly, it is on a line of fractured rocks that stretches to the Atlas Mountains in North Africa, and further over to the European Alps. Fig. 1. The “Devil” sign that marks the start of the National Park, and the site of a parking space. The fractures formed, and are still moving, as a … Read More

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europe geology volcanoes

Thrihnukagigur: An icelandic volcano

Dr Trevor Watts (UK) In 2012, my wife Chris and I booked a volcano tour around the north of Iceland. At the time, it was our third visit to the country, so we knew of extra things we wanted to do. Before joining the group with Volcanic Experiences of Bromsgrove, in the UK (www.volcanicexperiences.co.uk), we decided to have three extra days on our own. An hour on the Internet allowed me to book three unforgettable events. That really is all it took – and, incredibly, every company sent an email confirmation of my booking before the afternoon was finished. Fig. 1. The high point of Eyjafyallajokull’s rim – still steaming and too hot to sit down for long. The first was a 4 x 4 ride and then a three and a bit kilometre hike to the top of the now-famous Eyjafjallajokull volcano – still so hot underfoot that a dog with another group fled howling from the top of the ridge (Iceland Rovers: icelandrovers.is or http://www.2iceland.is).The second was a two-hour ‘Ice and Fire’ flight over the central part of the island, especially over the multi-coloured landscape of Landmannalaugar, with the campsite right at the edge of a lava flow (Eagle Airline, booked using Nordic Visitor: iceland.nordicvisitor.com).And the third was a trip down inside the emptied-out magma chamber of a volcano – Thrihnukagigur (insidethevolcano.com). And this is the subject matter of this article.Fig. 2. A view in the central highlands of Landmannalaugar, with multi-coloured hillsides, steaming vents, glaciers and a … Read More

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