Category Archives: Science

Spring

Around this time we celebrate the Spring Equinox, an important point in the yearly calendar but also, marking as it does the change from Winter to Spring with the hope of better weather and more light, good for the soul. Both the Spring and Autumn equinoxes mark the point when the Sun’s path is directly above the Equator, giving equal amounts of daylight and night (the word ‘equinox’ comes from the Latin term Aequus nox, equal night). This double hemisphere World map comes from a Dutch eighteenth-century atlas* and shows the paths of the Equator and the Tropics of Cancer and Capricorn, when the Sun is at it’s highest point for Northern and Southern summer and winter solstices.

Planisphærium Terrestre sive Terrarum Orbis…from Atlas Minor by Claes Janszoon Visscher, c1705. Map Res 85

The line of the Equator is described as ‘Æquator sive circulus æquidialis vulgo æquinotialis’  (‘Equator or equidistant circle’)

Here’s a page from a German atlas by the publisher Justus Perthes, circa 1910, explaining the way the movements of the Earth around the Sun (Erde und Sonne) create the solstices, equinoxes and seasons.

Page 2 from ‘Sydow-Wagners method. Schul-Atlas’ c1910. B1 (1745)

In Erde und Sonne different diagrams explain the journey of the Earth around the Sun, showing the tilting of the Earth on its axis that gives us the changing seasons. For the purposes of the blog figure 5 is the most important, Lauf der Erde um die Sonne (Erdrevolution), which shows the Earth’s rotation around the Sun. At the top is the Earth in relation to the Sun on the 21st of March, showing a perfect split between light and shade running from Pole to Pole,

This last third period of March has a number of ‘named’ and other important days. As well as the Equinox, the 18th of March, according to the Venerable Bede, was the first day of the Creation. This idea was due to Lady Day, the 25th, which was until 1751 considered the first day of the year. With the 18th being the first day of Creation it could then be worked out that, by a nice coincidence,  fours day later on the 21st the Sun, Moon and Stars were created, this is also St Benedict’s day. The 25th, Lady Day, marks the Annunciation of the Virgin Mary, nine months later it will be Christmas.

Mary is an important figure in the history of navigation. She is the Pole Star, a constant in the night sky and is also the saint of Navigators and, most useful on a journey, the ‘Virgin of Good Winds’. This image of the Virgin and Child comes from an early Portuguese portolan chart of the Atlantic. The cartouche with Mary in the centre is located in North America, a guide to those making the perilous journey across the ocean to the New World. Circling Mary are the words to the prayer ‘Ave Maria’, a prayer no doubt uttered on many a dangerous moment on-board ships, ‘…pray for us sinners now and at the hour of our death. Amen’.

[From an] Untitled portolan chart of the Atlantic, c1550 (MS) K1 (111)

*We have more than one edition of the Atlas Minor…, one edition uses gold-leaf at key points to highlight certain features, including appropriately enough, a Sun

 

Same but different

Location names get repeated throughout the World. Old and New York, Egyptian and Elvis Memphis, the list goes on and on. No one pair or group can have such a distance between them, and such a difference in what they are, as the Milky Way.

Der Südliche Sternenhimmel, c1899. A1 (42)

The Milky Way is one part of the Spiral Galaxy that includes our Solar System. Stars in their billions, so numerous that they appear as a river of milky light in the night sky. It is thought that there are as many planets as stars amongst the light. As with everything in the Universe size and distance defies belief, the width of the Milky way visible from Earth is 1000 light years across (light travels at 186,282 miles per second, 299,792 km, so in one year light travels 5.88 trillion miles, 9.46 trillion km. A trillion is one million million).

Here’s the Milky Way in two maps. First is a German map of the Southern Hemisphere from circa 1899 by the prolific Justus Perthes publishing house in Gotha. And then a later English map of the Northern Hemisphere from George Philip and Son in 1959. This is one part of a larger map which includes an equivalent  map of the Southern Hemisphere, a larger map of the Middle Heavens and lists and charts of stars and clusters. It’s easier to see from the Philip map how the Milky Way got its name.

Philips’ Chart of the Stars, A1 (10), 1959

The Milky Way is also a narrow bit of water between Noir and Kempe Islands at the western side of the Tierra del Fuego. It gets its name for the same reason, a milky appearance from a frothy stretch of white water. A book published in 1847, the North and South Atlantic Memoir, describes it as ‘a space of sea, in every part of which rocks are seen just awash with, or a few feet above, the water; on them the sea continually breaks’. The gentle name belies a dangerous passage between the islands with rocks clearly seen on the chart, a danger to any passing ship.

This extract comes from an Admiralty Chart of the Magellan Strait from 1887. The names on the chart give an indication of the hard landscape and dangerous sailing which abound. ‘Useless Bay’, ‘Desolate Bay’, ‘Famine Reach’, and the high number of narrow channels, many of which lead to a dead-end, show how hard it must have been for early explorers to navigate as opposed to sailing round Cape Horn. No wonder Magellan took so long to find a passage through.

Magellan Strait (formerly Magalhaen) sht 554, 1887

This chart shows the skills involved of the surveyors who measured, took soundings, kept records as well as lived onboard ship in such a harsh environment and the cartographers who then transferred this jumble of information on to a map. One of these surveyors was Commander Robert Fitzroy, of His Majesties Ship Beagle. This was Fitzroy’s first journey through Tierra del Fuego, his second, and more famous, was with Charles Darwin aboard as a companion and scientific officer. It was on this voyage that Darwin, after making numerous studies on the natural history of the lands explored on the voyage formed his theory of natural selection. In his book ‘The Voyage of the Beagle’ Darwin wrote ‘We passed out between the East and West Furries: and a little further northward there are so many breakers that the sea is called the Milky Way. One sight of such a coast is enough to make a landsman dream for a week about shipwrecks, peril and death…’. Fitzroy went on to become an expert on meteorology, forming what would become the Met office in 1854 and created ways to predict weather patterns, something which he gave a new name to, forecasts. A fervent Christian Fitzroy was horrified by the publication of Darwin’s ‘Origin of the Species’, the effect it would have religious beliefs and his role in helping Darwin form his theories by taking him on the Beagle voyage. Depression ran in his family, and Darwin’s fame together with financial difficulties and trouble with the Met Office led to Fitzroy taking his own life in April 1865.

Darwin’s importance can be seen in this  extract from the chart, with Darwin Sound and Beagle Channel appearing on a map just under 30 years after Darwin published his ground-breaking work.

 

 

Rocks rediscovered

Geological maps are often some of the most colourful and striking in the collection, especially the early ones on which the different rock types are coloured by hand. Luckily the Map Room receives all the geological maps published in the UK on Legal Deposit (as discussed a couple of weeks ago in this post on electronic Legal Deposit).

Research has been structured differently over the years, and at one time a large quantity of nineteenth century scientific mapping was transferred from the central Bodleian Library to the Radcliffe Science Library. Most of these maps have now been reunited with the rest of the map collection in the Bodleian Map Room, and a set of 39 large bound volumes of early geological maps has just been fully catalogued to modern standards. They include horizontal and vertical sections, detailed large scale geological mapping of certain counties, studies of areas of particular geological interest as well as standard series mapping of the British Isles at one inch to a mile. They have considerably enhanced the collection of early geological mapping.

Some of the most striking are detailed geological maps at the large scale of six inches to a mile; these are available for a few counties across England and Scotland. Most of the maps were based on Ordnance Survey mapping, made by military surveyors as early as the 1850s; the geological survey might be 20 or more years later.The early sheets were coloured by hand, often in astonishingly bright colours. This map of the area around Eastgate in County Durham was geologically surveyed in 1876-1877, published 1880. It’s at a scale of six inches to a mile. Paler blues represent sandstone and shale and the darker blue limestone, with basalt standing out in a vivid red; coal seams are picked out in gold. The maps were published by the Ordnance Survey.

The names of the geological surveyors for each sheet are generally recorded; this particular sheet was “geologically surveyed in 1876-77 by D. Burns, W. Gunn and C.T. Clough … under the superintendence of H.H. Howell.” The same names often come up repeatedly on many sheets. Fortunately, researching them is easy on the Pioneers of the British Geological Survey pages provided by the BGS Earthwise site. This has biographical information for dozens of early surveyors, sometimes including education, publications and even photographs of them in action.

The underlying geology of an area obviously has a profound effect on its landscape. This detailed geological map of Edinburgh from 1864 shows how the area around the castle, which is on a conspicuous hill above the city, is on basalt; the observatory is on another hill (mainly of felstone, now usually known as felsite, another igneous rock) to the east, while most of the surrounding area, coloured in grey, is sandstone.

These nineteenth century maps continued to be reproduced and updated well into the twentieth century, although the colour has long been printed rather than done by hand. This extract is from a one inch map of the area around Wigtown, first geologically surveyed in 1877 although this map was published in 1925.  The Map Room already held a considerable collection of these maps which has been augmented by the addition of the early volumes of geological maps. Modern geological maps continue to be published by the British Geological Survey at the slightly larger scale of 1:50,000.

Geological Survey of Great Britain : Durham. Southampton: Ordnance Map Office, 1880. C15 a.11/15. 

Geological Survey of Scotland : Edinburghshire. Southampton: Ordnance Map Office, 1864. C15 a.11/15.

Wigtown – Geological Survey of Scotland. Southampton: Ordnance Survey, 1925. C18 (33), sheet 4.

Юні друзі!

Young friends! This illustrated atlas of the Kiev region of Ukraine is a wonderful mix of both thematic and topographic maps and guides for young cartographers and naturalists. As the translated introduction says ‘This atlas is for those of you who are interested in geography and history, love nature. Explore your homeland in local history hikes and excursions’. The front cover has one of our young outdoor explorers striding out, his rucksack the outline of the Kiev Oblast.

Each double spread has a map or maps on the left with an illustration on the right of children doing something linked. So for instance where there is a thematic map on fauna, including diagrams for different bird boxes and animal prints, opposite is a picture of our naturalist heroes bird-spotting (Практичні поради юним біологам, or ‘Practical advice for young biologists).

There are pages on weather and climate, flora and minerals, along with topographic maps and town plans. The atlas is published by the Main Department of Geodesy, Cartography and Cadastre under the Cabinet of Ministers of Ukraine in 1997.

The atlas also includes illustrations and text on surveying techniques and, shown here, orienteering. Text above the star chart in the top corner shows how you can find north by looking for the Big and Little Dipper in the sky, while notes on the ground explain how studying the landscape can help find direction (мох укривае піеічний біх дерее і каміння, or ‘moss covers the north sides of trees’, for example). And then, finally, the healthy benefits of being a ‘young tourist’. 

Atlas yunoho turysta-krayeznavtsya, Kyyivsʹkoyi oblasti, 1997. C410 c. 3

Mapping radiation

On the 26th April 1986 technicians at the Chernobyl Power Plant in the Ukrainian SSR turned off the power to the number 4 reactor, hoping to test back-up generators used to keep the cooling waters circulating in case of a power outage. During the test the power-levels dropped to unexpected and dangerous levels. Following instructions that didn’t allow for such a possibility meant that the test proceeded, leading to a chain reaction releasing a huge amount of energy which immediately vaporized the cooling water, caused a devastating steam explosion and then the escape of a large radiation cloud. Wind conditions and proximity to the site meant that most of this radiation fell on the Byelorussian SSR.

This map, made post-independence in 1992, shows the density of pollution caused by Caesium-137 at different levels of contamination (a radioactive isotype that reacts with water, which as a consequence makes it easy to move around the body. It is one of the two most prominent isotypes released after the accident, and will continue to be a major health hazard in the area for the next two hundred years). The strong use of colours, more reminiscent of coloured-layering, is here used to show dramatically the area of contamination. There is also an inset of the area nearest the nuclear site showing strontium and plutonium radiation (Chernobyl is at the bottom centre of the map, Черновыль). What the map doesn’t show, of course, is the human cost to this tragedy. Only the title, ‘…until January 1992’, hints at a lethal problem still in place 6 years after the event. An updated version from 1993 manages to convey this cost though. Text in a number of languages states ‘…a catastrophe broke out – the major break-down of the power unit at the Chernobyl Nuclear Power Station. By its scale, complicity and long-term consequences it is the most severe catastrophe throughout the entire World history of atomic energy use…after the Chernobyl accident Belarus has become the zone of of the ecological disaster‘.  The text is in a number of languages; Russian, English, French, German and Polish, and when you carry on reading you realise why. As well as a map to show the spread of radiation following the accident the map is also a plea for international aid, ‘But the extent of the consequences of the catastrophe of the Chernobyl Power Station is so enormous that, it is regrettably, impossible for Belarus to liquidate them alone. The Republic badly needs medicines…The Byelorussian people, guiltless victims of the severe catastrophe, need the help of the international community.’

This extract comes from the back of the 1993 map, which includes the appeal for international aid. The three maps show the spread of the contaminated cloud between the April 27 and May 1st.

Maps have played a crucial roll in showing the aftermath of the Chernobyl incident. From tracking the contaminated cloud spreading across Eastern Europe to the more long-term mapping of contaminated lands maps have been the most useful medium to show the immediate and long-term effects of the disaster.

The Bodleian holds maps from the International Atomic Energy Agency, the Office for Official Publications of European Communities and the Hungarian Academy Research Centre for Astronomy and Earth Sciences as well as commercial publishers on Chernobyl and there are a number of interesting websites on the disaster, including Chernobyl Exclusion Zone Map – Chernobyl 35 years later, New mapping of radioactive fallout in Western Europe | EU Science Hub (europa.eu) and  ESA – Mapping Chernobyl fires from space

Карtа Радиационной Обстановки на территории Республики по на Январь 1992 г (Map of the radiation situation on the Territory of the Republic until January 1992) 1992 C403 (101). The 1993 map, Republic of Belarus. Review – topographic map with the data on radiation contamination is at C403 (104). Both maps are at 1:1,000,000

 

I do here, good reader…

In a time of uncertainty here on Earth it’s reassuring to look to the heavens for a more stable  environment, one in which we can predict what will happen with remarkable accuracy considering the vast expanse of space. This amazing map, ‘A scheme of the Solar System with the orbits of the Planets and Comets belonging thereto, describ’d from Dr. Halley’s accurate table of Comets…founded on Sr. Isaac Newton’s wonderful discoveries, by Wm. Whiston, M.A.’ shows with a great amount of information how a complex system of orbits and planetary bodies  work together and present a predictable path through time and space.

‘A scheme of the Solar System with the orbits of the Planets and Comets belonging thereto, describ’d from Dr. Halley’s accurate table of Comets…founded on Sr. Isaac Newton’s wonderful discoveries, by Wm. Whiston, M.A., 1712, (E) A1 (3)

William Whiston (1662-1752) was for a time Lucasian Professor of Mathematics at Cambridge University, and he also lectured on Natural Philosophy in London. He produced this map in 1712 with the noted map and globe maker John Senex to illustrate the course of comets as predicted in  work by Sir Edmund Halley and the ground-breaking work on planetary motion set out by Sir Isaac Newton.

The map shows the orbits of  ‘about twenty one known Comets…’.  according to Halley’s calculations (there are now over 3,000 recorded Comets in the Universe), the orbits of the Planets and, at the top, the relative size of the 6 known primary Planets and the Moon (the size of the Sun is represented by the outer circle of the map of the Solar System).

There is a remarkable amount of explanatory test on the map describing the six Planets and the ten secondary Planets (which we would know call the moons of the Earth, Jupiter and Saturn) and descriptions of the system of Comets and the Sun. Like all good exponents of a new theory Whiston makes a bold claim for his map at the start. ‘I do here, good reader, present thee with a scheme of the Planetary and Cometary World, part of which hath of late been called the Hypothesis of Pythagoras or Copernicus, but is now so certainly known to be the real system of nature that it ought no longer to have that uncertain title of hypothesis applied to it’. It’s amazing how many maps produced around the 1700 and 1800s include some form of claim such as this, or include in the tile ‘A new survey..’ or a variation on that phrase. The text goes on to acknowledge the size of the Universe and then ends with crediting the Creator, ‘As to the Fixed Stars, they are vastly remote from our Planetary and Cometary system but may perhaps every one be the center of another Solar System. Dr. Hook and Mr. Flamsteed think they have discovered their annual parallax and that is about 45″ which will imply there to be 900,000 millions of miles distance from our Sun; or according to Hugenius’s calculation in the like case much further than a bullet shot out of a canon could go in 100,000 years. But of such vast and numberless systems…we know very little, only so much we know of ye Planetary and Cometary World, and of the probability of Fixed Stars…as is sufficient to make us cry out with the Psalmist O Lord, how manyfold are thy works! In wisdom have you made them all!

Robert Hooke (1635-1703) produced most of the surveys of London after the Great Fire of 1666 and went on to try and measure distances to stars using parallax, which takes  the difference in angles of a measured distance seen from two different points. John Flamsteed (1646-1719) was the first Astronomer Royal and wrote star atlases and catalogues which were more detailed than any previously published. Hugenius is the Latin version of the name of the Dutch polymath Christiaan Huygens (1629-1695), one of the leading scientists of his or any other age. One of Huygens many contributions to science was the discovery of Saturn’s ring system and the first of the Planet’s moons after making improvements to the telescope. Hooke and Halley were involved in a wager offered by no less than Sir Christopher Wren while the three were at lunch in 1683 to discover why the Planets orbited the Sun in an ellipse, and not in a circle as suggested by Copernicus. To find the answer Halley travelled to Cambridge to talk to Isaac Newton, at the time Lucasian Professor of Mathematics ( Whiston replaced Newton in the role in 1702). Not only did Newton have the answer to the question but following promoting by Halley wrote his findings up in one of the most important Scientific books ever written, the Mathematical Principles of Natural Philosophy, more commonly known by the first word of the original Latin title, the Principa. In  this book Newton set out his three laws of motion and explains how the orbits of the celestial bodies work and the nature of gravity. Newton’s ideas in the Principa and Halley’s work on comets are the key to Whiston’s map.

John Senex was a noted map and globe maker and uses text at the bottom of the map to promote his products, extolling the worth of his maps and globes while also warning of the inferior products made by others based on his work. There are two of Senex’s globes on display in the Rare Books and Special Collections Reading Room at the Weston Library (the globe of the heavens  is shown here), possibly the two mentioned in the text ‘ He maketh ye newest globes of 16. 12. & 3 inches diam. and has just finish’d in a most elegant manner a pair of 28 inches diam. fit to adorn public librarys, or of the librarys of the most curious’. Senex has featured on this blog before, first in a

piece about globes (http://blogs.bodleian.ox.ac.uk/maps/2019/01/28/golden-globes/) and then, and more relevant to this piece in a post about a map of South America (http://blogs.bodleian.ox.ac.uk/maps/2019/02/22/a-tale-of-two-maps/) which is dedicated to Halley and marks the point where, during a voyage to map the magnetic variations in the Earth, Halley’s ship the Paramore encountered ice for the first time. Halley then produced a map of the World with the variations shown, which would enable navigators to plot a correct course using a ship’s compass with corrections made according to the variation shown

Halley’s magnetic chart [a facsimile from 1870 of Halley’s  ‘New and correct chart shewing the variations of the compass, 1701] (E) B1 (382)

Heliometer Domes and OS maps

The Ordnance Survey 1:500 map series are amongst the most detailed of all town plans. Dating from the 1880s and covering all towns with a population over 4,000, at this scale roofs come off important buildings to show the layout of the rooms underneath. While going through the maps covering Oxford this intriguing building appeared, the Heliometer Dome, part of the Radcliffe Observatory buildings.

The Observatory moved to Pretoria in 1934 hoping for clearer skies than could be found in Oxford, the buildings are now part of Green Templeton College. As well as showing on a beautiful map the Heliocentre has other cartographic claims for appearing in a map blog as it was a device crucial for measuring distances in space. The telescope in the Heliometer has a split lens, one of which is fixed in position, the second adjustable, thus producing a double image of either nearby stars or either sides of the Sun. By moving one of the lenses these images can be superimposed and then the different lengths of the lenses can be measured which will give the difference in distances between stars, a concept called parallax.

The Heliometer Dome circa 1860.

This next map is an extract from Robert Hoggar’s celebrated map of the city from 1850. At a scale slightly less detailed then the Ordnance Survey (1:528 as opposed to 1:500) at the top of this blog, like the OS map Hoggar maps individual trees and outbuildings, unlike the OS Hoggar includes contour lines.

Plan of the City of Oxford. 1850 (E) C17:70 Oxford (1)

This last image is the front cover from a record of the magnitude of stars according to their observable light recorded at the Observatory in 1853.

We’ve blogged about Parallax before http://blogs.bodleian.ox.ac.uk/maps/2015/07/10/parallax/  and about Ordnance Survey 1:5000 town plans as well http://blogs.bodleian.ox.ac.uk/maps/2018/03/01/pretty-in-pink/

True north

We are used to having north at the top of our maps. This has been the most common orientation for hundreds of years, largely because of the use of the magnetic compass. Compasses do not, however, point exactly north. The northern magnetic pole wanders around the Canadian Arctic, and anyone requiring precise direction for navigational purposes needs to keep this in mind. It is common for maps to have a diagram showing the difference between magnetic and true north, as in this sea chart from 1870 (which also includes a date for the declination and, elsewhere on the chart, the current rate of change).

The discovery that the earth’s magnetic field fluctuates, and does not line up with its geographical axis, is nothing new. European navigators were aware of this issue from the fifteenth century. Edmond Halley had begun charted the magnetic declination across much of  the world at the end of the seventeenth century, and this map by John Senex from 1725, based on his work, shows the “Line of no variation in the year 1700” curving sinuously across the Atlantic. Lines of equal declination – isogonic lines – are marked around it.

This line where magnetic and true north coincide – properly called the agonic – is also in constant motion and we recently heard the exciting news that it is about to reach the Royal Observatory at Greenwich, so compasses there will point to true north for the first time in 360 years. More information can be found here on the website of the British Geological Survey.

KA-BOOM!!!!

With the eruption of its volcano on the 26th of August 1883 the landscape of the island of Krakatoa changed in an instant. Over two thirds of the island disappeared in the explosion,

unleashing a tsunami that killed at least 36,000 people in the immediate area and created waves of sufficient power to register on tidal readings as far away as the English Channel.

New chart of Sunda Straits, 1883. D32 (103)

This map is a remarkable record of the changes caused by the eruption and subsequent tsunamis, made by Captain Morris of the Australian steam-ship ‘Chyebassa’ on the 2nd of September 1883, 136 years ago today. Morris states on the map how “We came through the Sunda Straits after the earthquake and found the Southern or Main Channnel perfectly clear. Flat Cape light is not burning, though the lighthouse is standing. Anjer and Anjer lighthouse is completely swept away [as can be seen in this extract from the map showing both the previous and post-eruption coastline]. The coast is very difficult to recognize, the whole of the trees which lined the shoreline are gone…The Government have a steamer cruising off Flat Cape, to warn vessels not to take the Bezee Channel, as it is completely blocked. There is also a vessel for the same purpose off Nicholas Point. We put Batavia [modern Jakarta] pilot on board the ship off Flat Cape for the “Roma”; after passing Nicholas Point, you must take the Northern passage, as all the buoys are away in the South pass”.

The explosion of Krakatoa was a truly global event, and news of the eruption was transmitted around the world via the telegraph cable (called on the map a submarine cable) which linked Java with the World by the cable laid through the Straits which connected Australia to London via Singapore. A message sent from Java could get to London in as little as three hours. Global in another way, as countries as far away as England and the United States felt the effects of Krakatoa in less violent ways. Sunsets were affected by the dust thrown up into the atmosphere and the remnants of the Tsunamis that swept the region were recorded on tidal gauges as far away as the English Channel while changes in weather patterns were registered in Los Angeles.

In 1888 the Royal Society of London produced a richly illustrated report, ‘The eruption of Krakatoa and subsequent phenomena’ (Vet A7 c.45) which gave detailed accounts, causes and the effects caused the eruption.  Included are watercolours of the sunsets over Chelsea

and a map of the reach of the waves caused by the explosion, that proved so devastating to those near the volcano, throughout the World

The introduction to the report gives some idea as to the confusion and damage to lives and property caused by Krakatoa.

‘ During the closing days of the month of August, 1883, the telegraph–cable from Batavia carried to Singapore and thence to every part of the civilised World the news of the terrible subterranean convulsion – one which in its destructive results in life and property, and in the startling character of the World-wide effects to which it gave rise, is perhaps without parallel in historic times.

As is usual in such cases, the first report of this tremendous  outburst of the volcanic forces appear to have been quite misleading and altogether unworthy of credence. Nor is this to be wondered at. The towns and villages along the shores of the Sunda Strait were, during the crisis of the eruption, enveloped in a terrible darkness, which lasted many hours, and, while thus obscured, were overwhelmed by a succession of great sea-waves; those who succeeded in saving their lives amid these appalling incidents were, it need scarcely be added, not in a position to make trustworthy observations upon the wonderful succession of phenomena occurring around them’.

Opposite this page is the illustration of the volcano at the top of this blog post.