First, some discussion about the fall of ash in "The Mammoth Hunters" by Jean Auel.
Source for the paragraph below:
Campi Flegrei (Phlegrean Fields) is a caldera approximately 12-14 kilometers across, located around 25 kilometers west of Vesuvius and 15 kilometers west-southwest of Naples. The caldera formed after a large eruption 35,000 years ago that produced 80 cubic kilometers of dense rock. Several other eruptions of decreasing intensity have occurred since then; its most recent eruption was in 1538. Since Roman times, Campi Flegrei has undergone vertical ground movements. During 1982-85, several ground upheaval and subsidence events were reported. ...
Source for the paragraphs below:
The stratigraphy of the second terrace above the floodplain of the Don and of the large ravines was the basis for relative chronology which was established by A.N.Rogachev in the middle 60th in cooperation with the geologists M.N.Grishchenko, G.I.Lazukov, A.A.Velichko. The sequence of deposits from the top up to bottom represents by following succession: chernoziem, followed by loess-like loams, and two humic beds, separayed by non-humic loams with lenses of volcanic ash..........
The background for the division of lower and upper humic beds is the horizon of the sterile loam containing lenses of volcanic ash. According to analytical investigations, the age of the volcanic ash can be regarded at 35-32 kyr, (35-32 thousand years ago) and can be attributed to one of the eruptions of Campi Flegrei in Italy.
Source for the paragraphs below:
40.827 N, 14.139 E; summit elev. 458 m
The volcano of Campi Flegrei lies immediately to the west of Napoli, and its deposits form much of the hills on which the higher areas of that city have been constructed. Less conspicuous as a volcano than neighboring Vesuvio, the Campi Flegrei must be considered one of the most dangerous volcanoes in Italy, mostly because of continuing unrest and dense population within the caldera and in its immediate vicinity.
Volcanism has occurred in the Campi Flegrei area during the past 50 ka (50 thousand years ago), including two extremely violent explosive eruptions, the one that erupted the Campanian ignombrite (35 ka ago) (35 thousand years ago) and another one only 12 ka (12 thousand years ago) which produced the Neapolitan Yellow Tuff. The erupted volumes show a general decrease with time, and the most recent eruptions were characterized by moderate to small volumes.
Then there's this paper. My thanks to Thalion for drawing it to my attention:
Paper No. 41-15
Presentation Time: 1:30 PM-4:30 PM
Y5 TEPHRA FROM THE CAMPANIAN IGNIMBRITE ERUPTION: A KEY CHRONOSTRATIGRAPHIC MARKER FOR THE MEDITERRANEAN AND EASTERN EUROPE
PYLE, David M1, RICKETTS, Graham D.2, SINITSYN, Andrei3, PRASLOV, Nikolai3, LISITSYN, Sergei3, MARGARI, Vasiliki4, and VAN ANDEL, Tjeerd H.5, (1) Earth Sciences, Univ of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom, firstname.lastname@example.org, (2) Queens' College, Univ of Cambridge, Silver Street, Cambridge, CB3 9ET, United Kingdom, (3) Institute for the History of Material Culture, Russian Academy of Sci, Dvortsovaya nab. 18, St Petersburg, 191186, Russia, (4) Department of Geography, Univ of Cambridge, Downing Place, Cambridge, CB2 3EN, United Kingdom, (5) Univ Cambridge, Downing St, Cambridge, CB2 3EQ, United Kingdom
The ca. 39 to 41,000 yr BP eruption of the Campanian Ignimbrite from the Phlegrean Fields, Central Italy, left a widespread tephra marker (known as the Y5 ash) that has been recognised in marine sediment cores across the Eastern Mediterranean. Recent work in the north-eastern Aegean and in south-western Russia confirms that a considerable portion of the Y5 ash was dispersed towards the North and East during this eruption, with fine-grained tephra deposited more than 2500 km from the known source region. In the Don River region of south-west Russia, deposits that are correlated with Y5 on the basis of detailed chemical analysis are found both in well-characterised archaeological contexts (the Paleolithic sites of Kostenki-Borschevo), and in undisturbed geological contexts nearby. The extent of dispersal of ash during the Campanian Ignimbrite eruption confirms this event as the largest known volcanic eruption in Europe of the past 100,000 years.
The Y5 ash represents a key event in the linking of marine sediment and terrestrial archaeological records. We present the results of ongoing work on the chemical and physical characterisation of the volcanic ash, and our interpretations of the significance of the ash-layer for the long-range transport of ash in large volcanic eruptions, and the chronology of the Upper Paleolithic.
XVI INQUA Congress
General Information for this Meeting
Session No. 41--Booth# 92
Correlation of Ice, Marine, and Terrestrial Sequences using Tephrochronology (Posters)
Reno Hilton Resort and Conference Center: Pavilion 1:30 PM-4:30 PM, Saturday, July 26, 2003
Life, the Universe, and Geology for EC fansSome basics. All the atoms our bodies are composed of, that are heavier than hydrogen (Carbon, nitrogen and so on), are the result of a complex series of nuclear reactions inside stars. Next time you cut yourself, reflect that the iron that gives your blood that rich, red colour was formed inside a star that exploded billions of years ago. Life was impossible until the first stars formed and turned into supernova, spilling their products into the universe to later coalesce into new solar systems such as ours, beginning the process all over again, this time with rocky planets circling the star.
The rocks which form such a large part of the background of the EC series are categorised (by people who like to pigeon hole things) into three groups:
Igneous- meaning out of fire, rocks that were once molten, for example basalt and granite.
Sedimentary- laid down by the actions of wind and water and ice moving usually small particles from one place to another, or by the actions of living organisms such as corals, for example sandstone, limestone and shale, and
Metamorphic- meaning changed in form, usually sedimentary rocks that have been transformed by heat and (usually) pressure to form often entirely different rocks, for example the slate (from mudstone and shale) used for roofing, and marble (from limestone) used for decorative facing.
First, igneous rocks. You may have heard of the phrase plate tectonics. It is a term invented in the 1960s to describe the movement of the earth's continents. Look at a map of Africa and South America. It is easy to imagine them fitting together. At one stage they were. (at the continental shelf level) A man called Wegener was laughed at when he did this sort of thing on a global scale at the beginning of the century, but he turns out to have been correct. The continents float around like rafts on a sea of heavier molten/fluid rock, bumping into each other, moving apart, and sliding past each other, creating earthquakes and volcanoes as they do. In fact this was used at one stage to find mineral deposits. A valuable deposit in Africa was found to continue in South America, right where Wegener said they were once joined.
Now when these plates move apart, it's like breaking your skin. You can't just have a huge gap, something moves up to take its place. In this case, the something is basaltic lava, because that's what the (mostly quartz rich) continents float on. Quartz (flint and common beach sand are examples) is lighter than the iron and magnesium that make up a lot of the minerals in basalt. Since it is mostly happening deep under the sea, it is usually a quiet eruption, but sometimes the gap is on land, as in Iceland, and volcanoes form. Even there, the volcanoes are usually well behaved, because basalt melts and solidifies at a relatively low temperature. This upwelling occurs in long ridges under the major oceans of the world. Hawaii is a special case, where there is a hot spot under the ocean floor, and as the ocean floor moves over the hot spot because of the movement of the plate, basaltic lava wells up above the hot spot, creating a chain of islands. If you count height above the base of a mountain as your measure, Mauna Kea on the big island of Hawaii is a lot taller (31 000 feet, of which only about 14 000 feet is above sea level) than Everest at about 29 000 feet. There is a new mountain forming now to the South East of the Hawaiian chain, at present below the the sea. Someday it will surface, creating a new island.
But what goes up must come down, and if some continents are moving apart, the other sides of them must be coming together, or at least grinding past each other, as the people in Turkey and on the West coast of the USA know only too well. When one plate or fault line moves past or over another, it tends to do so in bursts, rather than in a continuous movement, and the sudden movement results in earthquakes. This is what was happening when Ayla's people were lost down a crack in the earth, and when Creb was killed at the end of the Clan of the Cave Bear.
If continents come together, they can either both buckle up, pushing mountains higher, as is happening now in the Himalayas as the sub-continent of India crashes into the continent of Asia, or one can dive underneath the other, still pushing mountains higher, as is still happening in the Andes in South America. They tend to rise at a rate of a few centimetres (an inch or more) per year. The peak of Mount Everest is a little higher this year than last.
One of the most ambitious irrigation projects ever attempted in the world with hand tools came to grief when the Incas tried to divert one of the tributaries of the Amazon (flowing East) to the incredibly dry Western coastal desert, only to be defeated by the inexorable rise of the Andes causing the channels to send the water backwards. One can only imagine the consternation of the engineer when his plans came to naught.
And his fate when the Inca ruler wanted results, and got excuses. ('You are telling me that the land between the river and the desert appears to have risen since you took your last measurements? Hmmmmmm!')
So when one continental plate is grinding past another, tremendous heat is generated, sufficient to melt the rocks around. At this point there are two possibilities:
* Either the rock stays in place deep below the surface, and slowly cools, allowing large crystals to form as it solidifies, as in the case of granite or gabbro (called plutonic igneous rocks, after Pluto, the Greek god of the underworld, and ignis, the Latin word for fire, from which we get such words as ignition)
* Or the rock spews up onto the surface of the earth, the point of emergence becoming a volcano, and the liquid rock cools quickly, forming very fine crystals as in the case of rhyolite or basalt (called volcanic igneous rocks, after Vulcan, the Roman god of fire and metal working). If it cools really quickly, usually when the molten lava hits water, no crystals form at all, and you have a glass, such as obsidian. Makes beautiful and very functional spearpoints and knives. There's nothing special about flint except that there's a lot of it. Glass does just as well or better. The most beautiful bifacially worked points I've ever seen are called Kimberley points, after the Kimberley region of Northern Australia, and are formed from bottle glass, with superb workmanship, not long after the first white contact. When the first overland telegraph line was put in from Adelaide to Darwin, the engineers had a lot of trouble with the aborigines of Central Australia taking the ceramic and glass insulators on the telegraph poles to make spear points with. They found lots of uses for the copper wire, too. For one thing, it bound axe heads to handles really well!
There is one further difference: chemical makeup. You can simplify matters by thinking of two further categories of igneous rocks, acidic and basic.
Granite and rhyolite are made up of quartz rich materials. These sort of rocks are called acidic, with more than 50% silica, another name for quartz. Quartz is silicon dioxide, one atom of the element silicon combined with two of oxygen. Quartz sand is refined into the element silicon to form the basis for computer chips by removing the oxygen and purifying it to an extraordinary degree. (Silicone is a modern synthetic compound of silicon formed into long chains, used for glues and plastic surgery implants).
Their high melting/solidifying temperature means that when the quartz rich material reaches the surface of the earth, it cools and solidifies rapidly, very often blocking the hole it is coming up out of, with the expected results. The pressure builds up, and the volcano explodes. This is what was happening in the Mammoth Hunters when the volcanic ash was settling on the countryside after Rydag's death. The ash was quartz rich crystals that had had time to cool high in the atmosphere after a volcanic explosion before drifting down. Lucky they had. Pumice stone is the same stuff, often washed up on beaches, but where the ash was hot enough to melt together again on the surface of the sea into a light, porous material which because of its quartz and other hard mineral content is ideal to scour things. People use it to rub off hardened skin on the feet. Pumice is a hybrid igneous/sedimentary rock, since it comes straight out of a volcano, but is laid down by the action of sifting down through the air.
Gabbro, dolerite and basalt are made up of iron/magnesium minerals (called basic, with some quartz too, but not as such, but combined into silicates with the iron and magnesium. Basic rocks contain less than 50% quartz).
Because of the chemical makeup, the acidic rocks granite and rhyolite weather to form poor sandy, light soils for agriculture, while the basic rocks gabbro, dolerite and basalt weather to form rich, red/brown, 'volcanic' soils, very suitable for growing things. This is why the sides of basaltic volcanoes are very often used for agriculture. The soils are rich. Hawaii is a great place for growing tropical fruits, since not only is the climate ideal, but also the soils are full of nutrients.
Sedimentary rocks are ones laid down by ice, wind and water. When igneous rocks weather, the constituents (say of granite) degrade and separate into mainly quartz grains and clays, which are then carried away under the influence of gravity and running water, mainly. They tend to be in obvious layers, such as sandstone and shale, but not always. Limestone is laid down by corals (in shallow warm seas) and lime secreting algae and by chemical action, and is often apparently layerless, as is till, the sediment laid down by glaciers. Flint, a form of quartz, occurs as nodules in beds of chalk, the same chemical as in limestone, calcium carbonate, and containing minute fossils of marine organisms. Chalk is usually soft and crumbles easily, releasing the flint. Both these last occur in sediments formed from the skeletons of minute animals which use either calcium carbonate or quartz (silica) for their framework.
In increasing size of particles, you have shale, sandstone, and conglomerate, the last being a combination of different sizes of particles, often from clay through sand to cobble stones. It is often laid down as a streambed in a fast flowing river. Like any other rocks, sedimentary rocks can be tilted and even overturned, but if this does not take place, the alternating horizontal hard and soft layers often lead to the formation of cliffs, since the soft layers weather away under the hard layers, which project from the cliff making vertical or overhanging rock faces, making waterfalls likely if a river or stream is entering another, or the sea. This is the origin of the cliffs of the Sharamudoi and the waterfall in their little terrace above the Donau near the present Iron Gates of Romania. The dust storms Ayla and Jondalar encountered occurred when glaciers ground rock into flour, which was then carried away by the dry wind, forming huge deposits called loess, (again often apparently layerless) contributing to the flat nature of the Ukraine steppes where the action of the Mammoth Hunters takes place.
Metamorphic rocks are those changed by heat and pressure. When, say, a shale is squeezed and heated by the actions of earth movements, new chemicals form. These are often flat crystals, with the flattening at right angles to the pressure. Mica is a good example of this sort of mineral.
Mica is the stuff used most often inside toasters around which electrical wire is wound, the wire getting red hot and toasting your bread. (My latest super duper gee whiz you beaut micro chipped never-burn-the-toast toaster seems to have some sort of synthetic mica. The toasters of my youth had proper sheets of mica. But they burnt the toast, no fault of the mica) It can be separated into broad, flat sheets, and is non conducting of both heat and electricity, making it ideal for the purpose. It seldom forms such large crystals however, and is more likely to take the form of shiny spots on a broken surface, often called 'fools gold'. You can often see mica glistening in the sand of a stream bed. (Iron pyrites is also called fools gold, since it forms yellow/grey crystals which superficially resemble the precious metal. Iron pyrites is the mineral that Ayla used as a firestone. Struck against flint it gets hot enough to form long lived sparks as it burns, sufficient to ignite dry tinder. Steel and flint is what is used now in cigarette lighters, but the effect is the same)
The flakes of mica all in one direction contribute to a very common property of metamorphic rocks - many of them split easily. Slate is used for roofing because it can be split into thin waterproof layers, because of the often invisible crystals of mica which nevertheless are there all lined up perfectly together in the one direction, perpendicular to the original direction of the pressure which helped form them. Examples of metamorphic rocks and minerals include marble, serpentine, soapstone, asbestos, slate, phyllite and gneiss. Gneiss can easily be mistaken for granite, since it contains much the same sort of minerals in the same large crystals, but it has a banded appearance which distinguishes it from granite if you can see a large enough specimen of it.