Despatches: Soufrière Saint Vincent

OGG member, Patrick Sudden received a modest research award from the Oxford Geology Group Community Chest which contributed to his research visit to St Vincent in the Windward Isles.  This is Patrick’s account of his visit.


After arriving, I spent the first day at the CAASHI workshop. The day before a scenario had been developed of what would happen in a likely future eruption, including where pyroclastic currents would be found, and where the ash would likely be dispersed. We then prevented this scenario to a group of St Vincent residents, all of whom would likely have to take on a leadership role in the event of an eruption. They then discussed the planning for movement of supplies and people, long term planning, maintaining sufficient provisions and continued monitering as the scenario unfolded.

For the 2nd and 3rd days I attended the St Vincent and the Grenadines annual national conference, which this year was focussed on disaster risk reduction. At this conference some of the findings from the workshop were presented by some fellow volcanologists from the University of East Anglia, there was a presentation on past eruptions and their records which included some of my own research, and some further presentations on the geographical distributions of risk following an eruption.

I then had a couple of days to see a bit more of St Vincent and experience the culture. I visited the botanical gardens (the oldest in the western hemisphere) and the Fort Charlotte, used by the British to subjugate the local Carib population in the 19th century. Finally I was also able to visit the volcano I am studying. The hike up started in mountain rainforest, passed into cloud forest and then upland thicket on the upper slopes. I was fortunate enought to have much clearer conditions than the other unlucky geologists who had ascended the week before, but were unable to see anything when they reached the summit.

The crater wall is not the same height the whole way around, that is because the currently active crater is on the Southern slopes of the volcano, with the true summit to the North. Much of the crater walls are produced from pyroclastic rocks from previous eruptions, and generate scree slopes on the flanks of the crater. On the crater walls some black bands can be seen, these are ancient lava flows, signs of more effusive activity in the distant past compared to modern eruptions which only produce viscous lavas which form domes rather than easily moving lava flows. The most recent such dome can be seen in the centre of the image (below), it has been party revegetated since its formation in 1979. The 1979 eruption started with an explosive phase forming sucessive plumes 10-18 km high. After the former crater lake had been boiled away the style of activity changed to the slow growth of the dome in front of you. The white area on the lower slopes of this dome shows the currently active venting with steam and other gases being emitted. The smell of sulfur was very strong even from the top of the crater walls and the smell of sulfur in local villages has made many locals falsely believe an eruption could be imminent.


This image shows the North wall of the crater. At the very back, shrouded in cloud is the summit of the mountain. This back wall forms the Somma Wall, probably formed in a pre-historic eruption. In the foreground in the wall of the currently active ‘old crater’. The dip in this wall reveals the presence of the ‘new crater’, which is thought to have formed during an eruption in 1812.


This is an image (below) of the pyroclastic flow down on the East coast. It was likely produced during the 1902-3 eruptions- the focus of my project. It is estimated these eruptions killed more than 1500 people.


STREVA website: @STREVAproject

 Drawing fossils

OGG member Andrew Orkney describes a bivalve from the Wessex Basin.

This is a depiction of a single bivalve valve, from a beach in the Wessex Basin. Bivalve fossils with both valves are rare, because Bivalves spring open after death, and the valves separate.

The shell retains some original aragonite, especially near the dorsal side, and is filled in with glauconitic green sandstone.

The original aragonite shows that the fossil is relatively young, and the glauconite is consistent with a source from the Greensand, which was deposited in the early Cretaceous. The Greensand was deposited slowly on a submerged continental shelf, accumulating many fossils and providing the right conditions and time scales for the diagenetic alteration of iron-bearing minerals into glauconite.

The Greensand is friable, which means it releases its fossils when it is weathered at outcrop.



FOCUS ON: Dry Sandford

Dry Sandford Pit  is a 4 ha site has been a SSSI since 1950 and is now a BBOWT nature reserve. The rock exposures at Dry Sandford Pit are of Middle Oxfordian Stage (Late Jurassic) deposited circa 140 million years ago, in shallow coastal waters close to coral reefs.

Two geological formations are present at Dry Sandford:

Stanford Formation (Coral Rag member)

Kingston Formation (Beckley Sand Member)

The middle Oxfordian Stage is sub-divided into two ammonite time zones, each defined by the occurrence of a diagnostic species. One zone is characterised by Cardioceras densiplicatum and the other zone by Cardioceras tenuiserratum. As both ammonite zones are represented at Dry Sandford Pit the site is regarded as scientifically invaluable, local and national middle Oxfordian reference section.

Oxford Geology Group has published a new ‘FOCUS ON: Dry Sandford’ page on the OGG website

The page features photos, a log, bed by bed description and video.

Geological Illustration

This image demonstrates the difference between schematic and tonal illustration. A tonal illustration will be time-consuming, and in some cases tone fails to pick out, or even obscures details that are evident to the eye. This is one reason why cameras, which make images based on only tone and hue, and neglect prominence differences that are evident with stereoscopic observation, can often be misleading.

A schematic illustration is a ‘short hand’ way of expressing observation of a fossil. Details which are not relevant to your interest can be neglected, lending emphasis to the important features you have preserved.

Schematic illustrations usually denote changes in a specimen’s, texture, geometry, prominence or colour, with a sharp edge, producing a cartoon that is simple and accessible, compared to a truer rendition.

In this example, I have emphasised the trilobite anatomy’s segmentation.


Deep Time.

OGG member Paul Goodrich writes…

When astronomers talk of distances, they talk in AU’s ; Astronomical units, or Parsecs. The AU is the mean distance to our star, Sol, the Sun. It is 149,597,870,691 km, or thereabouts. A Parsec on the other hand is; 3.26 light years or 31,000,000,000,000 or 1.91735116 × 1013 miles. Even a parsec with all those noughts is still only three quarters of the way to our nearest intra galactic neighbour, Proxima Centuri. And most of the stars you can see at night unaided, are a thousand times more distant than that. Particle and nuclear Physicists on the other hand, go in the other direction. They go to microns, nanometres and Angstroms. More noughts with a decimal point way over to the left this time.

Numbers with a lot of zeros behind them begin to lose meaning, so terms like Parsec and Angstrom are used – to give a clearer concept of scale and for easier handling of equations. Well, at least for Astrophysicists. Conceptualising scale is important. I mean, when asked, how big is that water melon, one wouldn’t suggest that its about forty seven squillion bajillion oxygen atoms across. Thirty centimetres would be more appropriate, or one foot in old money. Geologists have similar difficulty in calculating quantities. Amounts of recoverable reserves in hydrocarbon reservoirs for example, or the volume and mass of the Earth. We use powers or orders of magnitude.

So when asked by a student, how heavy is the Earth? the long answer is 6,000,000, 000,000,000,000,000,000 kilograms. The short answer is, it has an approximate mass 5.975e24 kg. Neither makes much sense, so analogies are often used, like piling up bags of sugar all the way to the moon. Then there is pressure. If I dig a hole 35 km deep by one metre square and placed a hand specimen of mudstone and a pressure gauge at the bottom, back filled and tamped it neatly down, what would the pressure be down there with all that backfill over it? Excavate the hole for a second time and our gauge will have recorded about 30 MPa/km or 1050 MPa, or something over a billion tonnes per square metre. Actually, our pressure gauge would not have survived the experiment and the lump of dull mudstone would now be a nice shimmering piece of slightly smaller slightly denser – schist.


But the most perplexing concept of all, to Geologists, Physicists and Philosophers, is that of time. We all experience it, seconds and hours – months and years. A decade is a long time. A century is barely beyond the experience of everyman and a millennia is utterly unknowable. In the 17th Century, Bishop Ussher calculated that the Earth and all things in existence came into being on October 23, 4004 BC. Which would make the Earth, its vast oceans, it deserts and mountains, flora and fauna, just over 6000 years old. A reasonably comfortable number. Still big, but agreeably comprehensible. So when occasional heretics came along and questioned this concept of time, or at least – that there could have been so little of it, they were met with scepticism, derision and often outright hostility.

Geology as a science was in its infancy, it was lumped in with ‘Natural Philosophy’ practiced by gentlemen of means, aesthetes and ironically, some notable clergymen. When they pointed at rocks with their great bands of strata piled on top of each other, they wondered out loud, how it could be that it took so little time for grains of detritus to gather together and create such immense edifices as observed by Hutton, Lyle, Sedgwick and Murchison? And so the concept of Deep Time was postulated. To stand on a beach and see the waves slowly wear away the rocky cliffs and beach outcrops, 6000 years could not seem enough, not nearly enough. Rivers, winds and ocean currents carrying sand and clay minerals must surely need vast tracts of time to deposit enough material to create rocks thousands of miles square and thousands of metres deep.


Only for those rocks to be worn away, tilted on their side and the whole process repeated in great successions above an unconformable division or contact between the two rock type of different color and composition. Yes, Siccar Point! Tens or hundreds of thousands of years – perhaps, blasphemously, even millions of years were required to deposit, sculpt and shape the lands these pioneers of reason, science and art walked upon in search of answers and enlightenment. Over the next two and a half centuries, the Science of Geology and its Earth Science siblings of Palaeontology, Geophysics, Geochemistry and Geomorphology were providing answers, missing pieces of an enormous puzzle.
By the time of Lord Kelvin, an age of 100 million years was – while remarkable, acceptable.

His calculations based on heat reached the not unreasonable conclusion that a molten globe the size of the Earth and the dissipation of heat therein would require that amount of time to cool to its present level. Kelvin as an old man, was present at a lecture given by Ernest Rutherford, a luminary of the University of Manchester – wherein Rutherford spoke of radioactive decay and the energy/heat it produces. The products of that decay, the parent and daughter isotopes could be established, Kelvin heard of Uranium transmuted to Lead, of unstable and stable elements, and lastly – how this process dates the Earth. For the last century, accurate dating has made sense of the great piles of strata, ocean floors, mountains and the fossilised flora and fauna therein.

Radiometric dating is now a commonplace concept. Modern geologists often find it difficult to grasp just how the early pioneers worked, severely disadvantaged as they were by the lack of accurate chronology. Relative dating produced the now familiar periods from the Cambrian to the Cainozoic. These were accurate only in their division of time, of periods, eras and epochs when sands, muds and extinct biota were deposited, eroded and redeposited. The Ordovician for example was known for its Graptolites, Trilobites and other marine fauna in the rocks of the ancient Avalonian North Wales Basin. But over how long these rocks were formed and for how long the benthic creatures endured, was unknown for over a century.

Now, a visit to the labs at the Williamson Building in Manchester with a small sliver of Graptolite bearing slate will give an absolute date with a narrow margin of error. We can say that the Ordovician was a period of about 45 million years, book ended by mass extinctions at 488.3 mya and 443.7 mya. My small fragment of it was from the Caradoc, Soudleyan age, about 462 million years old. Give or take.

Finding Zircons in the Canadian Shield or the Cratons of South Africa and Australia, give reasonably accurate dates back to the Archean at 3850By to 4.400By. A mind boggling temporal distance from – for example, the Cambrian Explosion – the great diversification of life still over three billion years in the future.

Fragments of meteorites push the Earths formation further still to 4.54By. Or 4.54 × 109 years. More incomprehensible numbers. We can’t see these great periods of time, touch them or feel them. Its not something easily visualised or conjured up in the minds eye. So we go back to analogies and thousand word pictures. There have been have been the familiar clocks where the human race stands at a few seconds before midnight, and Sir David Attenborough’s moving band of time, diminishing to a vanishing point behind us.

I am a Geologist with an appreciation of the concept of Deep Time, but I value these depictions of past eons. To times when there was a Heavy Bombardment , the softened craters of which exist only in the Cratons, the remainder wiped clean by erosion and tectonics.

To the time of great oxidation events, of Snowball Earth, of Large Igneous Provinces, the first Terrestrial Plants, the great Mass Extinctions, to the closing of the Tethys and the opening of the North Atlantic, to the country where I live, only very recently sculpted by glaciers and planed by mile high Ice Sheets, ending a very short 8,000 years ago.

A comprehensible number indeed.

All Images, Open source Creative Commons.

Echinoid test

Kristian Fox writes:



Above is a relatively intact echinoid (sea urchin) test, found in Jurassic Inferior Oolite. Echinoids are members of the Phylum Echinodermata. As with other members of the Phylum – think of Asteroidea (starfish), echinoid show in the mature form 5 fold symmetry, the larval form is bilateral. This is rare in the animal kingdom but relatively common in plants, roses for example.

The major distinction in Echinoids are between regular and irregular. Being relatively spherical this is a regular echinoid, and much like a sea urchin you may picture. The mouth is on the underside and crunching mouthpieces (often referred to as an Aristotle’s lantern) are useful for eating other benthic sea life. Irregular forms, such as the ‘Sand Dollar’ are flatter and have the anus offset from the centre, this better allows them to burrow in sediment.

The Masaya Experience

OGG member Nikola Rogic writes about a recent visit to Masaya, Nicaragua…

The Masaya Volcano in Nicaragua is persistently active—that is, it erupts constantly—but it does not spew out molten rock; instead, it releases a steady plume of gas continuously.


When most people picture an active volcano, they probably don’t imagine one like the Masaya in Nicaragua—they picture giant ash clouds and lava flows that wipe out forests and towns. But just as a violent eruption dramatically alters the landscape around it, the Masaya’s plume powerfully shapes its environment. We know, for example, that crops often fail downwind of the volcano. But what else does this constant flow of gases do to the world around it?

NR 5

A research study may systematically analyze how the Masaya Volcano affects its environment.To trace the path and ultimate fate of the gases emitted by the volcano, we must start measuring from the volcano’s magma and moving through the gas plume into the soil, water, and ultimately, plants and animals. Knowledge of how volcanic pollutants travel and where they end up can help local people live more harmoniously with the Masaya by cultivating more acid-tolerant crops, for example, and developing safer evacuation plans.


Masaya Volcano releases harmful gases—it’s critical to know where they enter the food chain.


The volcano can also give us insight into the global impact of persistently active volcanoes. To address human-induced climate change, we need a better understanding of natural processes like volcanic eruptions. Although eruptions increase the amount of carbon dioxide in the atmosphere and contribute to the greenhouse effect, the impact of volcanoes is much smaller than that of burning of fossil fuels by humans. Volcanic eruptions also have a cooling effect, because the sulfur-rich gases they propel into the atmosphere form clouds that reflect solar radiation back into space.


With continuous scientific research at Masaya we hope to learn more about how volcanoes like the Masaya fit into this very complex picture.

NR 3




Photos credit: Nikola Rogic
Gravity measurements being taken at various localities (scientific stations) Masaya volcano, Nicaragua, Feb 2013