This category can only be viewed by members. To view this category, sign up by purchasing Annual subscription, 12 Month Subscription or Monthly subscription.

Plate tectonics (Part 4): More on the rock cycle

Helen Gould (UK) In Plate tectonics (Part 3): The rock cycle, I presented an overview of the relationship between the rock cycle and plate tectonics, and then went on to look more closely at igneous rocks. This time, I want to discuss sedimentary and metamorphic rocks, and review the occurrence of the rock cycle in the Solar System. Sedimentary rocks Sedimentary rocks, by contrast with igneous and metamorphic rocks, have no crystalline structure, being made up of little lumps of non-crystalline material derived from weathering other rocks. However, where they have been built up in horizontal layers, they may contain large-scale structures such as bedding. What are bedding planes? When sedimentary rocks deposited underwater (for example, limestones), they may be periodically exposed to the atmosphere due to tectonic uplift or a fall in sea level, perhaps because water is locked up on land as ice. The fact that it may take a thousand years to deposit a centimetre’s-worth of limestone places bedding planes into a context of millions of years. Fig. 1. Garnet micashist. Fig. 2. Garnet. Limestones are deposited in shallow seas, forming from the rain of billions of shells of sea animals onto the seafloor. Deposition stops if the area is exposed to the air and restarts when the sea covers it again, so a gap (bedding plane) forms. Many sedimentary rocks are laid down underwater and may contain bedding planes. In addition, the grain size, the fossils that are present and other lithological features all may vary … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Plate tectonics (Part 3): The rock cycle

Helen Gould (UK) What is the rock cycle? Usually, the first thing that budding geologists learn about rocks is that there are three kinds: igneous, sedimentary and metamorphic. These three major kinds are divided up into many different types of rock. For example, marble, slate and metaquartzite are all metamorphic rocks; basalt, granite, obsidian and andesite are all igneous rocks; and limestone, sandstone, clay and siltstone are all sedimentary rocks. What is a rock made of? Rocks are made of minerals. Therefore, particular combinations of minerals help us to identify rocks. Minerals are chemical compounds, consisting of chemical elements, which in turn are made of atomic particles. Who first thought of the rock cycle? James Hutton was the first geologist to propose a cycle of rock creation and change. In 1785, he gave a talk to the Scottish Geological Society in Edinburgh. In it, he suggested that rocks undergo processes that change them from one type of rock into another. He later developed the idea in his book, ‘Theory of the Earth with Proof and Illustrations’. He thought there was a relationship between the three basic rock types: igneous, sedimentary and metamorphic. We now know this is correct. Fig. 1. Agglomerate, Fig. 2. Andesite. However, it was not until this idea was set in a plate tectonics context that it really made sense to geologists. At about the same time, another Scotsman, James Hall, invented experimental geology. He demonstrated the crystallisation of basalt under slow-cooling conditions, and produced marble by … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Plate tectonics (Part 2): A closer look

Helen Gould (UK) As we saw last time (Plate tectonics (Part 1): What are they?), the Earth is a pretty dynamic place, with tectonic plates moving about on the surface, driven by convection cells in the upper mantle. But producing a workable theory, which combined most of the observations of geological evidence, took years. It was known that the centres of continents were extremely old, and that some areas around the continental “cratons” didn’t seem to belong because they contained completely different types of rocks. Combining continental drift with seafloor spreading and mantle convection currents produced the idea of plate tectonics, and provided an explanation for the odd rocks on areas fringing some cratons. These “microplates” had come from other areas of the Earth, where different geological processes had produced different rock types. The role of density in recycling: oceanic and continental crust The physical features of the ocean basins and continental mountain ranges are known as the “crustal dichotomy” (splitting of the crust into two equal parts), and because these types of feature are essentially dissimilar, they have their own rock types. Basalt is the commonest rock both in the Solar System and on Earth, where it forms the ocean floor, along with various sedimentary rocks deposited underwater which make up another 5% of the total oceanic crust. Continents typically consist of coarse-grained rocks related to granites, which solidify below ground. Comparing similar-sized pieces of basalt and granite in the hand will establish obvious physical differences between them. Basalt’s … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Plate tectonics (Part 1): What are they?

Helen Gould (UK) What does “plate tectonics” really mean? The Earth’s surface bears about 20 plates, which are able, over millions of years, to move about on layers beneath the crust. Some of the surfaces of these plates consist of continental crust, some of oceanic crust, some both (Fig. 1). Fig. 1. Map of the tectonic plates of the Earth. Who came up with the idea? The idea didn’t develop overnight as a result of one person’s efforts. In 1915, Alfred Wegener suggested “continental drift”, in which the continents moved around on the Earth’s surface. Arthur Holmes later suggested continents could be moved by convection currents in the mantle, fuelled by the heat of radioactive decay. Harry Hess was an American geologist who came up with the idea of seafloor spreading. In the 1960s, J Tuzo Wilson developed the convection current idea further, proposed “hot spots” and “plates” and, in 1963, Fred Vine and Drummond Matthews proved the existence of seafloor spreading using “magnetic striping”. What proof is there that plate tectonics really exists? The fit of continents against each other, particularly Africa and South America, shows that they were once joined (Fig. 2). This branch of geology – palaeogeography – has led to the detection of several ancient supercontinents and oceans. Their existence is supported by matching similar geological features, such as ancient crystalline rocks and glaciated areas, in adjacent regions of South America and Africa, and North America and Europe. Two massive continents, which existed in the past, … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

The Deccan Traps, India (Part 4): Quaternary sediments of the Godavari River basin, Maharashtra

Mugdha Chimote (India) The discovery of Quaternary sediments around Godavari River in Maharashtra (Fig. 1) was something of an accident. Sankalia (1952) first encountered these sediments while excavating the Lower Palaeolithic Industry in the region. Upon discovery, Sankalia brought onboard many geologists, such as Prof S N Rajaguru, Shanti Pappu, Gudrun Corvinus and R V Joshi, to bring an interdisciplinary approach to the study. Based on their geomorphic studies, Sankalia et al. (1952) concluded that the Quaternary palaeoclimates differed from present climates: the bedload stream represented wet climates, while the fine-grained sediments represented dry climates. Following this discovery, the Archaeological Society of India conducted similar such studies in the Narmada, Pravara and Tapi basins. Fig. 1. Location map of the study area. Quaternary records of upland Maharashtra include colluvial (material transported by the action of gravity) and alluvial (material transported by river) sediments. Along the river channels, alluvial sediments occur as discontinuous outcrops, whereas those in the basins do not exceed a thickness of 50m. Quaternary sediments account for the recent geological strata, which lie on the uppermost layers of earth and have been exposed relatively to the least amounts of erosion. The Earth underwent dynamic climatic variations in the Quaternary period, from glacial-interglacial events, development of monsoonal wind patterns, the formation of deserts and palaeomagnetic reversals, to mass extinctions. These incidents in turn led to geomorphic processes, such as the rejuvenation of rivers, alteration of those rivers’ courses during each rejuvenation and the occurrence of flash floods. It is … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

A field guide to Barbados (Part 6): Central Barbados

Stephen K Donovan (The Netherlands) Stop 1. Waterford District, near Codrington Agricultural Station (approx. 59º 36’ 8” W 13º 6’ 49” N; Fig. 1) The area considered in the final part of this guide is outlined in A field guide to Barbados (Part 1): Introduction (Donovan & Harper, 2010, fig. 1e) and Fig. 1 in this article. As with other articles in this series, the starting point is Bridgetown. Fig. 1. Locality map showing the positions of Stops 1 to 6 in central Barbados. Only those roads relevant to this excursion are shown (after Donovan & Harper, 2005, fig. 12). This figure should be used in conjunction with the geological map of Poole & Barker (1983) and any tourist road map. Key: abc = ABC Highway; B = Bridgetown; 1 = Waterford district (Stop 1); 2 = Dayrells (Stop 2); 3 = Harrison’s Cave (Stop 3); 4 = Welchman Hall Gully (Stop 4); 5 = Horse Hill (Stop 5); 6 = Hackleton’s Cliff (Stop 6); coastline stippled. From the ABC Highway, turn southwest towards Bridgetown on Highway 3. In the area of the turnoff towards Codrington Agricultural Station (on the right), in the parish of St Michael, examine the road cutting, starting at the southwest corner and walking northeast. This is Stop 6 of Humphrey & Matthews (1986, p. 101), in the Middle Coral Rock, just above the First High Cliff and dated at 194,000 years old. The succession shows a range of reef-related biologically-determined facies (that is, sedimentary rocks … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

A field guide to Barbados (Part 5): The Scotland District

Stephen K Donovan (The Netherlands) Stop 1. Chalky Mount (approximately 59º 33’ 15” W 13º 13’ 55” N; Fig. 1) The area considered in this part of the guide is outlined in Donovan & Harper (2010, fig. 1d) and Figs. 1 and 2. As with other articles in this series, the starting point is Bridgetown. Those wishing to examine the succession and structure of the Scotland District in considerably more detail than outlined below are referred to Speed (2002). This can be complimented by Patel’s (1995) discussion of the geomorphology. Readers are referred to the glossary in A field guide to Barbados (Part 2): The coastal geology of southeast Barbados Fig. 1 Locality map showing the positions of Stops 1 to 7 in the Scotland District of Barbados (after Donovan & Harper, 2005, fig. 11). Only those roads relevant to this excursion are shown. This figure should be used in conjunction with the geological map of Poole & Barker (1983) and any tourist road map. Key: C = Conset Point; H = Horse Hill; W = Welchman Hall; Stop 1 = Chalky Mount; Stop 2 = Bissex Hill; Stop 3 = Coconut Grove; Stop 4 = exposures on East Coast Road; Stop 5 = oil seep; Stop 6 = Bathsheba; Stop 7 = Bath Cliff; coastline stippled. Fig. 2 Geological map of the Scotland District of Barbados (after Donovan & Harper, 2005, fig. 2; Donovan, 2010, fig. 3; simplified after Speed, 2002, fig. 9). Key: open stipple = basal complex; … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

A field guide to Barbados (Part 4): Bridgetown and the South Coast

Stephen K Donovan (The Netherlands) The area considered in this part of the guide is outlined in Donovan & Harper (2010, fig. 1C) and Fig. 1 of this article. As in other articles in this series, the starting point is Bridgetown. Fig. 1. Locality map showing the positions of Stops 1 to 5 on or near the south coast of Barbados (after Donovan & Harper, 2005, fig. 8). Only those roads relevant to this excursion are shown. This map should be used in conjunction with the geological map of Poole & Barker (1983) and any tourist road map. Key: A = Grantley Adams International Airport; abc = ABC Highway; C = Six Cross Roads; O = Oistins; 1 = the Barbados Museum, Bridgetown (Stop 1); 2 = South Point Lighthouse (Stop 2); 3 = Foul Bay (Stop 3); 4 = Woodbourne Oilfield (Stop 4); 5 = Chapel Quarry (Stop 5); coastline stippled. Stop 1: The Barbados Museum The Barbados Museum and Historical Society was founded in 1933. Its museum occupies St Ann’s Garrison, a nineteenth century British military prison. It is situated in the parish of St Michael, southeast of the central part of Bridgetown, behind the Garrison Savannah racetrack. The museum has displays covering many aspects of Barbadian history and life, including natural history, prehistory and maps. The library is an important research resource, containing 5,000 books, monographs and articles on the culture and natural history of the island. Articles about the island’s natural history, culture and history are … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

A field guide to Barbados (Part 3): Northern Barbados

Stephen K Donovan (The Netherlands) Stop 1: Arawak Cement Quarry The area considered in this part of the guide is outlined in Donovan & Harper (2010, Fig. 1b) and Fig. 1. As with other articles in this series, the starting point is Bridgetown. Drive north from the Bridgetown area on Highway 1, the main west (or leeward) coast road, which is constructed on the Lower Coral Rock and overlies superficial deposits. Fig. 1. Locality map showing the positions of Stops 1 to 4 in northern Barbados (after Donovan & Harper, 2005, fig. 7). Only those roads relevant to this excursion are indicated (including the track to Stop 4). This map should be used in conjunction with the geological map of Poole & Barker (1983) and any tourist road map. Key: C = Content; Ch = Checker Hall; G = Greenidge; T = Trents; 1 = Arawak Cement Quarry (Stop 1); 2 = Animal Flower Cave, North Point (Stop 2); 3 = limestone cliffs west of North Point (Stop 3); 4 = Cluff’s Bay (Stop 4); coastline stippled. The First High Cliff and the Middle Coral Rock are close by in the east (Speed & Cheng, 2004). This coast has been developed for tourism and has neither the magnificent sea cliffs of the east coast, nor the impressive Atlantic breakers seen in the previous excursion. To the west, two submerged barrier reefs, at 22m and 70m water depth, are separated from the coast by a submerged wave cut terrace (MacIntyre, 1967). … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

A field guide to Barbados (Part 2): The coastal geology of southeast Barbados

Stephen K Donovan (The Netherlands) and David AT Harper (Denmark) Introduction This article is the second part of a field guide to Barbados, the first part of which is A field guide to Barbados (Part 1): Introduction. The areas visited by different the excursions outlined in Parts 2 to 6 of this guide are shown in Fig. 1. All itineraries commence from the Bridgetown area and the itinerary outlined in this part is rewritten after Donovan and Harper (2002). The words in italics and bold appear in the glossary at the end of the Part 1. Fig. 1. Relative positions of field excursions described in this field guide (after Donovan & Harper, 2005, fig. 5). (a) Southeast Barbados (Part 2). (b) North Barbados (Part 3). (c) South Barbados (Part 4). (d) Scotland District (Part 5). (e) Central Barbados (Part 6). Charles Taylor Trechmann DSc, FGS (1885-1964) (Fig. 2) was an anachronism, a twentieth century gentleman geologist and archaeologist. He was an amateur with sufficient private means to dedicate his time and use his scientific abilities to make an original contribution to his chosen field of study, an original thinker with a desire to use his observations to interpret broad geological phenomena. He devoted his time to research on Malta, Gibraltar, New Zealand and, particularly, northeast England and the Caribbean. He published over 80 monographs and research papers on geology and archaeology, including at least 40 on the Caribbean (Donovan, 2003, 2008, 2010a). Fig. 2. Charles Taylor Trechmann, DSc, FGS (1884-1964) … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

A field guide to Barbados (Part 1): Introduction

Stephen K Donovan (The Netherlands) This is the first of six articles that will introduce the geology of the Antillean island of Barbados. It is an expanded and more detailed guide derived from two earlier publications (Donovan & Harper, 2005, 2009). The structure of the guide will include a summary of the geology of the island (in this part) and five, one-day field excursions for the geologically-biased tourist. These excursions will introduce the stratigraphy, structure and geological history of Barbados (Figs. 1 and 2), a small Antillean island shaped like a contorted teardrop, about 34km long by 24km at its widest. Fig. 1. The principal features of the geological history of Barbados summarised in a single section at Spring Bay, parish of St. Phillip, on the southeast coast. Professor David Harper (University of Copenhagen) is looking northwest, towards Ragged Point (Fig. 2) and admiring the angular unconformity between the allochthonous Palaeogene basal complex (=Scotland Beds) and the overlying autochthonous bedded limestones of the Pleistocene Coral Rock. A visitor to the island, who wants to undertake fieldwork, should hire a car. The only other reliable forms of transport are bus and taxi. While cheap, buses tend to stick to the main routes, particularly in the countryside. However, the size of the island means that localities are rarely more than a few kilometres from a bus stop. If money is no object, a taxi driver will be happy to drop you at a site in the morning and collect you at a … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

The Deccan Traps, India (Part 3): Evidence of recent tectonic activities in Deccan basalts

Mugdha Chimote (India) The term ‘Quaternary’ is derived from the Latin word “Quaternarius” (meaning “four”, such that the Quaternary is “the fourth great epoch of geological time” in the now-abandoned system of dividing geological time). It refers to the most recent period of the Earth’s history, covering a span of about 1.77 million years extending up to the present day. The Quaternary System is divided into Pleistocene and Holocene Series. The term Holocene was introduced for the part of Quaternary that contains only living species. It covers the last 10,000 period of the Quaternary. The Quaternary has witnessed some very important events of great consequence, characterised by dramatic climatic changes. It witnessed repeated glacial and interglacial periods, more so than any other period of geological history. Monsoonal wind patterns also developed during this period, and deserts were formed during the latter part of the Quaternary. Although the Quaternary recorded a few extinction events, a great biological diversity still exists on Earth. Most of the present-day species of vertebrates, invertebrates and plants are believed to have remained unchanged during this period. By now, you must have realised, the Quaternary is not a separate entity of geology. It rather refers to the time period ‘Quaternary’ and all the geological processes pertaining to that period. Quaternary rocks and sediments are the most recent geologic strata, which lie on the uppermost layers of earth and have been exposed to the least amount of erosion. As such, they are one of the most well studied … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

The Deccan Traps, India (Part 2): Its geomorphology and stratigraphy

Mugdha Chimote (India) Fig. 1. The natural arch/bridge at Ahmednagar, Maharashtra (see text box below). The Deccan Traps occupy approximately 25% of the total of peninsular India, that is, the triangular shaped landscape of southern India. They traverse the states of Maharashtra, Karnataka, Madhya Pradesh, and Gujarat. The Deccan Traps are currently believed to occupy about 500,000km2 of northwest peninsular India. It is estimated that the total exposure prior to erosion (including the region beneath the Arabian Sea) is of the order of 15 million square kilometres (Krishnan, 1956) or even up to 18 million square kilometres (Todal and Eldham, 1999). The differences in estimations of the total area of the Deccan Traps resulted from the fact that, an unknown area of the Deccan Volcanic Province (DVP) was rifted away as the Cambay rift system moved south and the Seychelles-Mascarene Plateau, along with part of the DVP, migrated to the west. The earliest basaltic eruptions took place along the north-western margins of the Indian continent, that is, in the Nashik-Narmada region. Later lava successions were emplaced on the southern flank of the evolving volcanic edifice as India migrated northwards over the plume head. The last of the flows were erupted in the southern DVP near Belgaum in Karnataka. As a result, the thickness of the flows gradually reduces from north-western to southern region of Indian subcontinent. Given the massive extent and volumes of Deccan Basalts, extensive studies have been carried out over the years to better understand the petrography, geochemistry, … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

The Deccan Traps, India (Part 1): The story of its genesis

Mugdha Chimote (India) Fig. 1: Deccan Traps exposed in Mahabaleshwar region of Maharashtra, India. Introduction Sandwiched between the Arabian Sea to the west and the vast Indian subcontinent to the east, the Western Ghats, a haven for trekkers and travellers, are a 1,600km long range of mountains along western edge of Deccan Plateau. Also known as “Great Escarpments of India”, the range extends from Gujarat in the north to Kanyakumari in the south. The Ghats traverse the states of Maharashtra, Karnataka, Kerala, and Tamil Nadu. They comprise of more than 39 wildlife sanctuaries, reserve forests and national parks. The Western Ghats were declared as one of the eight hottest ecological hotspots in the world in the year 1988, as the area is home to nearly 325 globally threatened floral, amphibian, fish, bird and faunal species. Famous hill stations such as Mahabaleshwar, Panchgani, Munnar, Wayanad, Coorg and Ooty are among some of the perfect weekend getaways and popular tourist attractions here. Thanks to the rich ecological reserve and tourist attractions, Western Ghats were awarded the title of UNESCO World Heritage Site in 2012. The Western Ghats however cover just a small portion of Deccan Traps (see also box: Kaas Pathar below). Deccan is an anglicised word derived from the Sanskrit word “Dakshin”, meaning south (the region is located in the southern part of Indian subcontinent). “Traps” mean step-like features. Thus, the Deccan Traps are step-like volcanic features found mainly in Southern India. The laterally extensive basaltic lava flows of the Deccan … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Geological field trip through Scotland: Basalts from the Isle of Skye

Robert Sturm The Isle of Skye is a part of the Inner Hebrides in the north-west of Scotland. It has a total area of 174,000 hectares and has an irregularly shaped coastline that is typical of the British Isles. Since the early nineteenth century, the island has become a centre of geological research, because rocks of different geological periods are exposed there. For instance, the gneisses of the Lewisian complex were formed in the Proterizoicum, 2,800Ma and, therefore, are some of the oldest rocks in Europe. On the other hand, intrusive and extrusive igneous rocks can be assigned to magmatic events that covered wide parts of the island during the Tertiary. This event, which took place about 60Ma, resulted in the development of the Atlantic Ocean in its present form. In more recent times, two ice ages, which affected the island 26,000 years ago (the Dimlington glacial) and 11,000 years ago (the Loch Lomond glacial), resulted in the formation of a partly spectacular glacigen landscape (a landscape formed by the ice) with sediments that are of high interest for geological research. Fig. 1. Geological map of the Isle of Skye (modified after Anderson & Dunham 1966) illustrating the high variability of rocks that can be found on the island. Impressive evidence for the Tertiary volcanism is provided by the plateau lava series (these are horizontally stacked layers of lava), mainly exposed in the north and west of the island. These extrusive rock formations probably reached a thickness of 1,200m before … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Skye: Island of Dreams

Anthony Rybek (UK) Having lived on the Isle of Skye since 2007, I consider myself to be very fortunate to have every day opportunities to fulfil my hunger for the wilderness, natural world and two of my greatest passions, fossil hunting and geology. So, it was of no surprise to me that, during these times immersed in this dramatic and mostly unspoiled landscape, yet another passion would evolve – oil painting. Fig. 1. Anthony Rybek, working on a painting. Like all my pursuits, I am self-taught and, as I began to learn and practice painting techniques, it soon became clear that I had a degree of aptitude for this art form. I found it similar to my earliest fossil hunting trips where, once I tasted success and the thrill of discovering new and amazing fossils, the desire to learn more and improve my skills grew deeper and deeper. My painting is no different. It wouldn’t take long before the subject matter for my landscape paintings would cross paths with fossil hunts and geology. Skye has an abundance of iconic geological landmarks and I feel privileged to have a basic understanding of the geological processes that help shape these formations. And it is these dramatic scenes that are the main influence of many of my paintings. The Trotternish Ridge In the northern half of Skye, this is the dominant feature of the Trotternish Ridge, which runs like the spine of an ancient creature between the islands capital Portree and the infamous … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Along the Chain of Craters Road, Big Island, Hawaii: Part 5

Dr Trevor and Chris Watts (UK) This is the last of five articles on the ‘Chain of Craters Road’ on Hawaii’ Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Hawaiian pronunciationA word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.3.7 miles: the pahoehoe flow Adjacent to the road, this is a wide-spreading series of flows dating mainly from 1969 to 1974, from Mauna Ulu. In the southern part, the lavas also originate from the smaller volcano of Mauna Loa o Mauna Ulu. These are varied, but mainly formed as thin, smooth sheets. They were often broken up after solidifying by being pushed upwards into low mounds by fresh lava invading beneath them and also by the lava beneath them draining away, causing the thin skin to collapse. The forest that existed here is now seen as tree moulds. These are generally in an excellent, fresh condition, and … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Along the Chain of Craters Road, Big Island, Hawaii: Part 4

Dr Trevor and Chris Watts (UK) This is the fourth of five articles on the ‘Chain of Craters Road’ on Hawaii’ Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Hawaiian pronunciationA word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.3.7 miles: Mauna Ulu A short road to the east finishes in a large car park. The trail continues eastwards through the woodland (Fig. 1) for a few hundred yards until it opens out to a view of the twin peaks of nearby Pu’u Huluhulu and the more distant, and much higher, Mauna Ulu (Fig. 2). Fig. 1. A side trail into the forest close to Mauna Ulu car park. Fig. 2. Where the trail divides left and right. The dark a’a lava spreads across the lighter ash and lapilli flow. The twin peaks form Mount Pu’u Huluhulu; the more distant low rise is the shield volcano, Mauna … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Along the Chain of Craters Road, Big Island, Hawaii: Part 3

Dr Trevor and Chris Watts (UK) This is the third of five articles on the ‘Chain of Craters Road’ on Hawaii’s Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Hawaiian pronunciationA word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.2.6 miles: the Hi’iaka lava field and lava tree forest This is just across the road from the Hi’iaka Crater and is the later (May 1973) lava flow. It is very extensive and is little explored beyond the first 100 yards from the road. Before the eruption, there was a forest here, mainly of ʻŌhiʻa trees, but, on 5 May 1973, a series of fissures opened up and vast amounts of lava gushed forth (Fig. 1). Spreading over several miles, it devasted the forest, filled several former collapse craters, became ponded up at the Koa’e Fault cliff, and flowed away. It drained back almost to the original surface … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Along the Chain of Craters Road, Big Island, Hawaii: Part 2

Dr Trevor and Chris Watts (UK) This is the second of five articles on the ‘Chain of Craters Road’ on Hawaii’s Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Hawaiian pronunciationA word about Hawaiian pronunciation – Hawaiians do not say ‘Morna Ulu’ for the Mauna Ulu volcano. They split most vowels up separately: thus, ‘Mah ooner Oo loo’. Similarly, ‘Kill ow eh uh’, for Kilauea; and, ‘Halley mah oomer oo’, not ‘Halley mow mow’, for Halema‘uma‘u; and, ‘Poo ooh Poo ah I’, for Pu’u Pua’i.Down the Chain of Craters Road 0.3 miles: the July 1974 flow This flow, which was mostly pahoehoe lava, covered several hectares. It came from the nearby cone of Ma’una Ulu, a subsidiary cone of Kilauea. The eruption began in May 1969 and lasted until July 1974. It featured many periods of spectacular fire fountains, including one that reached 300m high on 30 December 1969 (Fig. 1). Fig. 1. Mauna Ula fire fountain 1968. (Source: USGS.) Spreading as far as the sea, it added 94 hectares of new land to Big Island – more than 230 hectares. In addition to spreading across the surface, much lava sank, returning … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Along the Chain of Craters Road, Big Island, Hawaii: Part 1

Dr Trevor and Chris Watts (UK) This is the first of five articles on the ‘Chain of Craters Road’ on Hawaii’s Big Island. The articles are in the form of a road trip that you can follow if you are lucky enough to go to this wonderful part of the world to see its volcanic scenery. Being a road trip in the USA, distances along the road and by foot are given in yards and miles, while measurements are provided in more European and scientific metric units. Introduction Kilauea volcano dominates the southeast of Hawaii’s Big Island. At 1,247m high, it is by no means the biggest or highest of Hawaii’s peaks, but it is easily the most active. It doesn’t have a peak. Instead, there is a caldera – a huge, oval-shaped collapse crater that formed 500 years ago in the space of a few days – perhaps a few hours. It now measures about 5km long by 3km wide, and is 165m deep (Fig. 1). Fig. 1. Regional sketch of Kilauea’s caldera and the Chain of Craters Road. Its appearance and dimensions have changed considerably over the years as different parts of the caldera have erupted at different times and in different ways. The most spectacular event in the past century was the 600m-high, fire-fountain episode in 1959, which filled the caldera floor with a lava lake and created the ‘side caldera’ of Kilauea Iki. The main eruptive point now is the fire pit known as Halema‘uma‘u that … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Book review: Hutton’s Arse: 3 billion years of extraordinary geology in Scotland’s Northern Highlands (2nd edition), by Malcolm Rider and Peter Harrison

If you can see past the somewhat robust title (a reference to James Hutton’s discomfort riding around Scotland on horseback during his geological investigations), this is an interesting read, combining both geological science and humour in just about the right measures.

Geo Junkets: New Zealand, North Island (Part 3)

Jesse Garnett White (USA) Kohioawa Beach and Matatā Escarpment, Putauaki Volcano and the Kawerau Geothermal Field Kohioawa Beach and Matatā escarpment Kohioawa Beach, an uninterrupted sweep of sandy beach, dunes and wetlands, is directly below the near vertical Matatā escarpment between the towns of Otamarakau and Matatā. The escarpment gradually gains elevation to its highest point behind Matatā. Infrequently cut by active and inactive canyons, flowing streams debouche across the beach into the Bay of Plenty. Atop the escarpment are rare, mature pohutukawa, puriri and manuka, and various types of scrub and grass. Part and parcel of the Whakatane Graben, the terraced escarpment is composed of Castlecliffian marine sediments, remnants of the Aranuian Interglacial period. On the western margin of the graben near Matatā, marine sandstone and siltstone outcrops contain bivalves, gastropods, crustaceans, sponge spicules and microfossils, overlain by tuffaceous sediments, ignimbrite gravels and conglomerate (Nairn and Beanland, 1989). The coastal dune and wetland areas of the Rangitaiki Plains and Tarawera River Valley near Matatā exhibit Holocene backswamp and floodplain deposits, including levees and meander sediments associated the Awatarariki, Waimea and Waitepuru stream catchments. The catchments rise from sea level to 370m elevation and drain into the Bay of Plenty. The Awatarariki and Waitepuru wetlands were destroyed in 2005 by large, storm-induced debris flows and associated floodwaters. Waimea was largely unaffected, retaining the majority of its pre-storm event character. Matatā township was severely impacted by debris flows, with over a hundred homes and properties damaged or destroyed. Prior to the … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

World of geology

Tony Waltham (UK) This article accompanies a book review of Tony Waltham’s book, The World of Geology. The text is broadly taken from the book itself. The world of geology is the world as we know it, that we see and that we live on. It is all about the evolution of the Earth’s crust, the nearly rigid layer less than 100km thick that is the outer shell of our evolving planet. This crust is broken into a few dozen large and small tectonic plates, which move around at rates of a few centimetres a year. Originally known as continental drift when it was first recognised in 1912, this geological activity has been referred to as plate tectonics since its processes began to be properly understood during the 1960s. A large part of the Earth’s crust is the oceanic floor. The basaltic rock of the slowly moving oceanic plates is continuously being created along plate boundaries that are divergent, and destroyed along those that are convergent. These are the major processes of plate tectonics that keep Planet Earth evolving and alive. The oceanic basalts are similar to those in some types of volcano, but otherwise they remain largely unseen beneath the cold, dark and minimally explored waters of the ocean depths. The second part of the Earth’s crust is the incomplete upper layer, largely of granitic composition, that forms the continents. Along with the submerged edges known as the continental shelves, these occupy about one third of our planet’s surface. … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Take me to the rocks

Dr Sebastian Lüning (Germany) I am a geologist by profession. Everyday of my working life, I have worked with rocks, from nine to five, for 19 years, looking for oil and gas in the Sahara. Sometimes this is stressful, sometimes really enjoyable and sometimes simply annoying – just like any other job. However, I’ll tell you a little secret about what I do in my limited spare time to refresh my mind and recharge my batteries for another day. I am so in love with my rocks that I am also a hobby geologist. I just cannot keep away from the rocks. There are plenty of interesting fields open to amateur geologists and palaeontologists to indulge in. Most popular are probably collecting minerals and fossils, including visiting quarries and searching beaches for new specimens. However, my hobby is focused on regional geology. I love to understand the earth history of a particular area, by visiting its outcrops and reading the regional geological descriptions that have been published about it. That is, I like to look behind the scenes of a modern landscape to understand how it was shaped and what lies underneath. I drive and walk through my object of study to understand its dimensions, distances and height. At one moment, I can pay attention to millimetre-sized fossils and, a few minutes later, be enjoying a panorama across kilometre-scale valleys shaped by ice. I am convinced there are many other amateur geologists, who share my passion for an integrated view … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

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

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.