Saturday, 12 July 2025

Visit the Holm Islands

 Visit the Holm Islands

Dr. Nick Chidlaw has proposed a trip to Steep Holm and Flat Holm. He has written an extensive introduction to the trip which I have repeated below. It sounds rather good.

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Dear All,

I am currently proposing a trip to study during 1 day the geology of the Holm Islands; these are located in the sea where the Severn Estuary and Bristol Channel meet. 

There are 2 islands, Steep Holm and Flat Holm, the former being part of England, and the latter Wales.  

I have run trips to study the geology there in the past, and they have enrolled well and attendees have greatly enjoyed visiting the islands and studying the geology.  I have also run indoor courses and given talks on the subject, and they have gratifyingly drawn good responses too. 

The plan is to duplicate as far as practical the field programme used on earlier trips.  This involves landing on Flat Holm, and studying the geology in beach sections and local crags, and sailing around Steep Holm, observing the geology from close inshore but not landing. This plan for Steep Holm is because most of the geology is best observed in its steep cliffs around the island; when on Steep Holm itself, much of this geology is not saffely accessible.  The sailing around Steep Holm is not done quickly - we spend over an hour going around, with many stops during which we discuss the geology visible at each key point.  

The rocks on both islands are of early Carboniferous age, mostly shallow marine with some indicating episodic emergence. The lithologies are limestones and dolostones with variations in grain size and shelly fossil content, and minor non-carbonate mudrocks. On Flat Holm is a limestone unit known only from that island. Many of the stratigraphic units can be linked to the nearby mainlands of England at Weston-Super-Mare, and in the Barry area in Wales.  The strata are extensively deformed by compressional folding and faulting that occurred during the Variscan Orogeny around the end of Carboniferous times c. 300 million years ago: on Steep Holm, the strata mostly dip gently to the S, but become steely-inclined,  in places 70 degrees, on its northern side; on Flat Holm, the island is mostly occupies a gentle upfold, plunging to the south west. There are reverse faults observable on Flat Holm together with minor folds superimposed on the main fold, and some impressive ripple structures in the limestone unique to Flat Holm. During the Triassic period, under a hot dry climate, the two islands formed 'inselbergs' surrounded by extensive flats that episodically became lakes. Crustal stretching during the Middle Jurassic c. 170 million years ago carried metalliferous brines up opening faults on Steep Holm, locally depositing galena and baryte. Before the end of the last glacial, c. 12,000 years ago, the sea was much further to the west, and the islands formed hils, between which the River Severn flowed in a narrow ravine some 45m below present sea level. With the ending of the last glacial, sea level rose to form the Bristol Channel and Severn Estuary, leaving the Holms as the islands we see today.

Date of the proposed trip

Saturday 30th August 

Transport & organisation

Rigid Inflatable Boat (RIB) operated by Bay Island Voyages Ltd out of Cardiff Bay.   It is to be appreciated that if the sea conditons on the day are unsuitable, the company will decide to cancel / postpone the trip for reasons of safety. 

Timings     

The Bristol Channel and Severn Estuary have some of the highest tidal ranges in the world; as can be appreciated, the proposed itinerary is strongly governed by predicted tidal conditions and currents. On this proposed date, the activities take place from 8 am, with the field party returned to Cardiff Bay by 2 pm.

The details are as follows :

0800     Meet at Cardiff Bay (check in, safety briefing, life jacket fitting. 
0830     RIB passes out through Cardiff Bay Barrage 
0850     Arrive at Flat Holm. Landing fee £5.00 per person (cash only, payable on arrival). We are allowed c. 2.5 hours on the island 
1120     Depart Flat Holm
c.1145  Arrive Steep Holm - circumnavigate island, with frequent pauses, for c. 1.5 hours. 
1315     Depart Steep Holm
1345     Pass through Cardiff Bay Barrage 
1400     Arrive Cardiff Bay

Fee

The fee involves payment to Bay Island Voyages Ltd for providing private charter transport, and tuition by myself. 

I will pay Bay Island Voyages their fee, from fees received from those who are interested and available to attend the trip. 

There are 12 places available on the RIB, 11 trip attendees and myself.  

The fee per person £125.00 

In case there is a good number of people interested and available, enrolments will need to be on a first-come first-served basis. 

If there are fewer than 11 who can attend the trip, the cost is likely to be too high per person if the private charter fee is shared between those who can attend; we will need to cancel the proposal should this be the case. 

If there are more than 11 who are interested and available to attend the trip, they can be put on a waiting list and Bay Island Voyages Ltd have said there may be another RIB available, but they do not know at the present time.  

If the trip can go ahead, I will sent a PDF of the trip document to all those enrolled in good time before the date of the trip. This will provide all logistical information attendees will need (including location of Bay Island Voyages car parking area and embarkation point) plus geological background. Attendees would bring printouts of the trip document with them for reference during the days programme. 

Viability Deadline

Bay Island Voyages Ltd has a busy programme, but they are helpfully prepared to operate a provisional booking with us for 2 weeks up to 14th July.

I must therefore make a definite booking with them, and pay their fee, by this set date.  If the payment and booking is not secured by that date, they will make the RIB avaiable to other potential users for 30th August. 

Payment to me
 
If you are interested and available for this trip, please forward me your fee of £125.00 by Saturday 12th July. 

I will let you know on Saturday 12th July if we can put the trip on. If we do not have enough enrolments, I will return your fee the same day. 

Please note enrolment requests are to be sent to:

Nick Chidlaw nickchidlaw@gmail.com
Some images are given below to illustrate the islands and the transporting vessel used. 

I hope you find this proposal interesting and that you can attend.  Any queries you may have, do let me know.

Holm Islands from South Wales

Flat Holm


Steep Holm


Holm Islands RIB

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The Oldest Meteorite Impact - Not Quite

 The Oldest Meteorite Impact - Not Quite

A correspondent has sent me THIS LINK which concerns a meteorite impact in Western Australia. The "Science Alert" article is based on THIS ACADEMIC PAPER and is also the subject of 

The burden of the article is that it refutes an earlier PAPER which claimed that the impact was the earliest known on Earth. The original dating was based on the very old age of the rocks in which cone structures were observed and an age for the impact of 3.47Ga. 

The later paper tells us that, in the same area, shatter cones have been found in younger rocks aged at 2.77Ga and they conclude that the maximum age of the impact is 2.71Ga - and the minimum a meagre 0.4Ga.

These papers are examples of the scientific method at work. I also note that the article in THE CONVERSATION illustrates its argument about superposition by using a photograph of the Siccar Point unconformity - the earliest described unconformity. Do I detect someone poking fun at the competition!

Thursday, 26 June 2025

Hydrogen - Is This the Fuel of the Future?

 Hydrogen - Is This the Fuel of the Future?

If you look at the current edition of New Scientist you will find many article about hydrogen exploration. I asked Google Gemini "List recent publications concerning geological exploration for hydrogen" and got THIS VERY INTERESTING ANSWER.

Hydrogen as a fuel is a very good thing - it's combustion leads to energy and water. Up to now the problem has been difficulties in making or finding it, storing and transporting it, and having the engines to use it. The infrastructure of the oil industry already exists and up to now, fulfils the needs of society.

But the advance of electric vehicles suggests that oil might be on the way out. Oil companies are no doubt aware of this. But electricity is not their thing. Finding and moving hazardous materials is. I suspect that they see movement from oil to hydrogen as fitting in with their expertise.

A movement from oil fuel to electricity might be difficult for them. A change from oil to hydrogen - not so much.



Saturday, 14 June 2025

A Dinosaur's Last Meal

 A Dinosaur's Last Meal

A correspondent, who is currently in the area, sent me the link to THIS ARTICLE which concerns the work done on an Upper Cretaceous sauropod (Diamantinasaurus matildae) found near the small town of Winton in the middle of Queensland, Australia.

The dinosaur, called Judy for reasons which need not detain us, is so well preserved that her stomach contents are preserved. This is the first time that we have direct evidence that sauropods were vegetarian. There is lots of indirect evidence that they must have been so but now we can see what they ate.

Also she is the first dinosaur fossil with skin preserved that has been found in Australia.


Small portion of Judy's skin, showing approximately hexagonal scales covered in tiny lumps (termed papillae). Scale bar in centimetres. (Poropat et al., Current Biology, 2025)

Judy's stomach contents confirm what had been thought - sauropods ate from trees high off the ground. But she was not fully grown and so, also ate low growing plants - angiosperms.

The work done on Judy is also discussed in THIS ARTICLE. The source paper for both is THIS ACADEMIC PAPER. The latter covers everything in painstaking detail. I particularly liked "The fossilised bones were exposed using standard digging equipment (e.g., hammers, chisels, screwdrivers, dental probes, paintbrushes)"


Saturday, 7 June 2025

Were There Five Mass Extinctions?

 Were There Five Mass Extinctions?

THIS ARTICLE in New Scientist questions whether there were five Mass Extinctions - end of the Ordovician (445 million years ago), the late Devonian (372 million years ago), the end-Permian (252 million years ago), the end-Triassic (201 million years ago) and the end-Cretaceous.

The evidence for mass extinctions is best seen in the marine environment, where fossil preservation is easier. On land preservation is more difficult. And so mass extinction is more difficult to prove. Or is it that mass extinction did not happen on land?

And if it did not happen on land, was it a mass extinction? On land, animals find it easier to move than sea creatures. Plants have seeds which can survive long after the parent dies. Insects, with there rapid regeneration times, seem to avoid extinction. (But have a poor fossil record.)

Much of the argument seems to come down to a matter of definition. Labelling the present day as the Sixth Mass Extinction might make conservation goals more difficult if it comes to arguing about definitions.

Wednesday, 28 May 2025

Down to Earth Extra June 2025

 Down to Earth Extra June 2025

The June 2025 edition of Down to Earth Extra has been published. You can download it HERE or you can read it below.


Saturday, 17 May 2025

Land Level Rises - What is the Cause?

 Land Level Rises - What is the Cause?

A correspondent sent me THIS LINK. It is based on THIS ACADEMIC PAPER. The reason for the papers is the measured rise in land level in South Africa. The rise is not much - 6mm in the period 2012 to 2021. The rise could be measured because of the extensive GPS network in the country.

But what is the cause of the rise? For several years the reason was thought to be the mantle plume beneath the region. But the research described in the papers suggests that the real cause is drought! If you think of the soil as a sponge, taking the water out will cause the sponge to expand. Therefore land level rises.

All very interesting but the research suggests that the GPS system can be used as a means of measuring the severity of drought and planning to mitigate the consequences of predicted water shortages.