Coat of arms and geology

Already in early times naturalists gathered in associations and societies to encounter fellows, share discoveries, publish research and why not - have a good time. In the 17th century the members of the Royal Society not only enjoyed a good coffee, but organized also every week lectures and public experiments to promote science.

The first Geological Society was founded 1807 in London, followed in 1830 by Paris, in 1836 by Tyrol and in 1848 by Berlin. Ironically if the request by the Tyrolean Alois Pfaundler in 1803 for the "Mineralogisch-geognostischen Vereins in Tirol (Mineralogical-Geognostic Society of Tyrol)" had been accepted, maybe the first in the list would be the small Austrian province and surrounding areas - known already for its peculiar minerals.

The Geological Society in London was a privately founded organization, first intended more as a small and elitist dining club for amateurs interested in geology. However already a year later the number of members had increased drastically, the society begun to organize a collection of paleontological and geological specimens and possessed a fast growing library.

Fig.1. The Geological Society in session in the first Somerset House meeting room with its "parliamentary" layout, ca. 1830, sketch by Henry De La Beche.

But the Geological Society did not yet possess an official recognition and Royal Charter. The society was not considered a legal institution, it could therefore not rent rooms for meetings and most concerning it was not considered owner of the great collection of books, fossils, rocks and minerals donated by the single members.
The official recognition by the monarchy was also an ambitious target to increase the prestige of both the society and the single members and the still young science of geology. Especially the conservative Rev. William Buckland, elected in 1824 as President of the Geological Society, was very ardent to achieve this prestige.

"fifteen years have passed since I was placed, by your kindness, in the honourable position of filling this chair, at that important period in our history when we received the national recognition of a Royal Charter. I shall never cease to consider it one of the brightest rewards of my labours in geology [. . .]"
BUCKLAND 1840

To gain the Royal Charter was not an easy task; it needed the support and connections to influential politicians, had to deal with possible opponents within and outside the society (especially the Royal Society considered the Geological Society a dangerous competition) and was an extraordinary financial burden for a such a society - only to submit a formal petition 300 pounds were needed, half the financial capital of the society.
Despite the emerging problems of rivalry and financial burden, in 1824 the society decided to prepare the petition and handle the draft to the authorities.  
April 23, 1825, the King approved and sealed with the Great Seal a Royal Charter creating the Geological Society of London as a Corporation. With the recognition of the society also the possibility of free accommodation in a public building - Somerset House - was possible and soon the society settled in the eastern wing of the new building.
With the benefit of one financial problem gone - to pay for room -  the members continued their work to organize the new society.

In a letter of the June 13, 1825 Henry De La Beche, noted geological caricaturist, offered a sketch for a proposed Coat of Arms for the new Society.

Fig.2. Henry De La Beche's proposal for a coat of arms for the Geological Society, 13 June 1825.  

De La Beche proposed that the coat of arms should include in the main shield a simplified section through a bone cave, apparently based on one of the plates in Buckland's Reliquiae Diluvianae (1823). The other upper quarter would have included three ammonites, beneath would be a geological section of the northern flanks of the Alps. Rampant skeletons of an ichthyosaur (on the left) and a plesiosaur (on the right) would serve as heraldic supporters of the shield.
De La Beche proposed that the crest above the shield should be the commonly found heraldic device of the bras arme´ - an arm wielding a weapon, although in this case the "weapon" would be a more inoffensive geological hammer.
But the idea with the coat of arms was not followed and finally (in 2007) replaced by a Geological Society logo used by William Phillips in 1811 on the original copy of the Society's Transactions.

Coat of arms with geological content can be still found, the English city of Whitby adopted three snake-stones (ammonites), and the Czech Republic is very proud of its fossils and role in the history of geology. The city of Skryje for example has in it civic heraldry even a trilobite, inspired by the species Skreiaspis spinosus (thanks to Dr. Astudillo-Pombo for the information). And Georneys presents the Dartmouth's Department of Earth Science logo (with typo).

Bibliography:

BOYLAN, P.J. (2009): The Geological Society and its official recognition, 1824-1828. In LEWIS, C. L. E. & KNELL, S. J. (eds) The Making of the Geological Society of London. The Geological Society, London, Special Publications, 317: 319-330
BUCKLAND, W. (1840): Anniversary Address of the President. Quarterly Journal of the Geological Society 3(68): 210-267

A geologist riddle #6

A new riddle – what was the following sketch meant to depict and what should it be good for?

De Loys' Ape

Louis François Fernand Hector de Loys, (1892-1935) was a Swiss geologist pioneer of the young science of oil fields prospecting; he travelled extensively and collected experience in Europe, Africa and America during the golden age of oil exploitation.
Unfortunately de Loys is less known for his geological achievements than for a strange story about a strange photography.

Fig.1. François de Loys (1892-1935), photo taken probably before his expeditions to Venezuela in 1917; however de Loys was only 25 when he visited the country, so the general impression of a young, intrepid geologist, probably also larksome, was still valid at the time of his adventures (VILORIA et al. 1998).

In 1920 a handful of exhausted men reached the bank of the Tarra River, a tributary of the Rio Catatumbo in the borderlands of Venezuela and Colombia. They were all what remained of a group of 20 prospectors of the Netherland oil company "Colon Development", which had ventured in the Sierra de Perijeé, a range of mountains, in 1917. In charge of the expedition, intended to geological map and study the region for a planned exploitation of the suspected oil reserves, was de Loys.
The area was not only a dangerous jungle infested with tropical beasts of prey, parasites and diseases, but also inhabited by the hostile Motilones Indians, they decimated one after another the members of the expedition. It seemed already that the expedition was a failure, but in the last part a strange encounter occurred.

One day de Loys spotted at the shores of the Rio Tarra two large, biped monkeys covered with reddish fur and without tails. The two threatening animals walked upright and begun to approach the expedition, visibly irritated, shouting, brandishing with the arms and finally defecating in their own hands and using the excrements as projectiles against the expedition. Finally the frightened men decided to respond to the attack, so they shoot in direction of the two apes and killed was seemed a female, meanwhile the male escaped in the jungle.
Since de Loys and his people had never seen such large monkeys, he tried to preserve the skull and take various photos of the body. However soon the skull begun to decay and during a trip on the river the boat capsized and most of the photos of the animal got lost.
When de Loys finally returned home with the only remaining evidence, a single photography which he treasured in his notebook, he forgot about his annoying encounter with the unknown monkeys. Only years later a friend, the Swiss anthropologist George Alexis Montandon (1879-1944), accidentally rediscovered the photo.

Fig.2. The notoriously photography of de Loys´ ape - Ameranthropoides loysi, from MONTANDON 1929. Note that there exist many versions of the image cropped by the borders, magnifying the impression left by the animal.

Considering the supposed dimension of the box (45-50cm high) visible in the photography the height of the animal was estimated to range from 150 to 160cm.
This seemed to confirm the measurements by Loys (157cm) and based on the dimension and the unusual human-like characteristics, especially the missing tail, in 1929 Montandon published a detailed description of the ape, which he considered a genuine species named "Ameranthropoides loysi", de Loys' American human-like ape.
The animal in the photography displays characteristics that are not found in the monkeys of the new world, like the upright posture, the absence of a tail and 32 teeth (after the description of de Loys). Montandon was fascinated from this sensational discovery of a supposed unknown ape species and began to collect anecdotes and legends of great apes present in remote places of South America (not specifically the region of the supposed encounter).
In two stone statues of the Maya period large, 1,5m high apelike figures are pictured. Among the tribe of the "Caribi" of Guyana there is a widespread belief in the "kanaima", demons which roam the jungle armed with clubs, assaulting whoever dares to enter their reign. In Colombia these creatures are called "didi" and described as half man and half monkey. In Brazil and Venezuela there are legends of the "vastiri".
Author and collector of curious natural history P.H. Gosse reports in 1861:
"It is, however, possible that a great anthropoid ape may exist, as yet unrecognised by zoologists. On the cataracts of the upper Orinoco, Humboldt heard reports of a "hairy man of the woods", which was reputed to build huts, to carry off women, and to devour human flesh [...] Both Indians and missionaries firmly believe in the existence of this dreaded creature, which they call vasitri, or "the great devil." Humboldt suggests that the original of what he boldly calls "the fable", may exist in the person of "one of those large bears, the footsteps of which resemble those of man, and which are believed in every country to attack women;" and he seems to claim credit for being the only person to doubt the existence of the great anthropomorphous monkey of America. But it might be permitted, in return, to ask what "large bear" is known to inhabit Venezuela; and whether it is true that bears´ footsteps have a signal resemblance to those of men; and that bears specially attack women."
In the book "Natural History of Guiana", published by Dr. Edward Bancroft in 1769, there is a description of an encounter with a creature like an "orang-utan", and naturalist George Edwards in "A study of anthropoid life" (1757) depicts a strange ape-like creature resembling the modern photography.

However this publication of Ameranthropoides became accepted only by the French scientific establishment, in contrast it aroused a violent controversy by scientists from Great Britain and North America, the eminent English naturalist Sir Arthur Keith for example affirmed that the photo showed only a species of spider monkey - Ateles belzebuth native in the region- with the tail deliberately cut off or hidden in the photography.
Spider monkeys are a typical element of the South American fauna; however the largest known species reach 110cm height standing on the hind limbs, De Loys ape was with the estimated 157cm considerable larger. The only known fragmentary remains of such a large spider monkey species (with an estimated weight of 25 kilograms more than twice the weight of modern spider monkeys) are those of Protopithecus brasiliensis, the "primitive monkey of Brazil", a Pleistocene species discovered by the Danish naturalist Peter W. Lund in 1838 in the Brazilian region of Bahia.
In 1990 however an American cryptozoological expedition seemed to confirm Montandon´s ethnobiological research, the locals of Venezuela told the expedition about large red monkeys and recognized the ape in the photo as momo grande, as "big ape", a supposed large unknown spider monkey species. However also this expedition could not provide hard evidence apart rumours of supposed encounters or unrecorded tracks of large monkeys.

The simplest explanation, the possibility that the photo was a fraud was refused on base of the good reputation of De Loys:

"It is sure that Francois de Loys was a man of strict science and responsibility, optimistic and friendly and featuring an intrepid spirit of adventure. It seems unlikely that such a scientist may have perpetuated the fraud of the Ameranthropoides only to gain fame. [...] There are sufficient reasons to affirm that de Loys was not a liar, especially one unimpeachable document as the original photo taken at a time when photography and image manipulation did not exist at all."
VILORIA et al. 1998 & 1999

This statement is surely to optimistic, photo manipulation is as old as the art of photography and the dimension or characteristics of the animal in many cropped versions of the photography can not be compared to other objects apart from the strange box.
De Loys himself was very reluctant promoting the story, in the official publication of 1929 by De Loys himself about the geological expedition there is no mention of the creature or subsequent research, he published only, hustled by Montadon, an article in the Illustrated London News.

In 1998 Pierre Centlivres and Isabelle Girod finally published an article suggesting that the entire story was an idea by anthropologist Montandon.
Montandon was strongly influenced by racist ideas of human evolution popular at the time; he proposed a polyphyletic origin of humans and considered the various human races descending from various local monkey species. He affirmed that Africans evolved from gorillas and Asians from orang-utans. A missing link as the supposed Ameranthropoides was a perfect example of an evolutionary line between spider monkeys and South American Indians and would have confirmed his racist hypothesis.

The most plausible hypothesis that emerges now is a manipulated photo of a common spider monkey of the species Ateles belzebuth, used by Montandon to promote his hypothesis of human evolution. This view is supported by a detail in the complete view of the photo - there are stumps of non-native, cultivated banana trees visible, it is highly improbable that in the middle of the untouched jungle, supposed location of the encounter, banana trees can be found.
In the July-August edition of 1999 the Venezuelan scientific magazine "Interciencia" published a letter send in 1962 from a certain Enrique Tejera to the editor Guillermo José Schael of the magazine "Diario El Universal":

"[...] This monkey is a myth. I will tell you his story. [...]
Mister Montandon said that the monkey had no tail. That is for sure, but he forgot to say something, it has no tail because it was cut off. I can assure you this, gentlemen, because it was before me that the amputations take place.
Who is speaking here in 1917 was working in a camp of the oil exploration industry in the region of Perijá. The geologist was François de Loys, the engineer Dr. Martín Tovar Lange. De Loys was a prankster and often we laughed at his jokes. One day they gave him a monkey with an ill tail, so it was amputated. Since then de Loys called him "el hombre mono" (the monkey man).
Some time later I and Loys went in another region of Venezuela: in an area called Mene Grande. He always walked along the side of his monkey, who died some time later. De Loys decided to take a photo and I believe that Mr. Montandon will not deny it is the same photograph that he presented today. [in 1929 Montandon presented the Ameranthropoides in a public lecture]
More recently during a visit to Paris my astonishment was great visiting the Museum of Man. On top of a monumental scale, filling the back wall, there was a huge photo with the caption: "The first anthropoid ape discovered in America."
It was a photograph of de Loys, beautifully modified. The plants were no longer visible in the background, and it was not possible to understand on which kind of box the monkey was sitting. The trick is done so well that within a few years the monkey will be over two meters high. [...]
Finally, I must warn you: Montandon was not a good person. After the war he was shot because he betrayed France, his homeland.

Sincerely, Your friend Enrique Tejera."

If the myths and rumours of large ape-like creature in South America have a zoological explanation, the photo of de Loys surely has nothing to do with them.
Despite his role in the pranke (he contributed the photo and the story and later never resolved the case), he continued his promising career in the field of exploration geology. In 1926 he engaged in the Turkish Petroleum Company, cultivating contacts with geologists and scientists all over the globe. In 1928 he became a fellow of the Geological Society of London and soon visited the Irak to study the geology and the possible oil reserves of the region. Here he encountered Syphilis, returned to the town of Lausanne in France where he died still to young, on October 16, 1935.

Bibliography:

CENTLIVRES, P. & GIROD, I. (1998): George Montandon et le grand singe américain. L'invention de l'Ameranthropoides loysi. Gradhiva 24: 33-43
GOSSE, P.H. (1861): The Romance of Natural History. 4th ed. Boston, Gould and Lincoln, New York: 280-281
MONTANDON, G. (1929) : Découverte d'un singe d'apparence anthropoïde en Amérique du Sud. Journal de la Société des Américanistes de Paris, 21 (6): 183-195
SHERMER, M. (2002): The Skeptic Encyclopedia of Pseudoscience. ABC-CLIO: 903
VILORIA, A.L.; URBANI, F. & URBANI, B. (1998): François de Loys (1892-1935) y un hallazgo desdenado: La historia de una controversia antropologica. Intercienca Mar.-Apr. Vol.32(2): 94-100
VILORIA, A.L.; URBANI, F.; McCOOK S. & URBANI B. (1999) : De Lausanne aux forêts vénézuéliennes. Mission géologique de François de Loys (1892-1935) et les origines d'une controverse anthropologique. Bulletin de la Société Vaudoise des Sciences Naturelles, 86 (3) : 157-174

Online Resources:

ROSSI, L. (13.12.2004): La Scimmia di Loys. (Accessed 16.01.2011)

The Eruption of the Revolutionary Volcano

The subversions ongoing in the North African countries of Tunisia, Egypt and Libya have inspired a cartoon found by Malcolm and presented on his blog Pawn of the Pumice Castle - the depiction, aside from the ludicrous concept of geology, compares the rage of the people with a sort of magma chamber soon to feed a volcanic eruption (in Egypt already successful).

The use of forces of nature as metaphor has a long tradition, especially phenomena as fire, floods or storms were often associated to negative historic events like war, invasion or plagues.
In the 18th century the European revolutions to overthrow kings and dictators, especially the French revolution of 1789-1799, changed this negative significance, now fast occurring social changes were like disasters with a positive aftermath - the old becomes destroyed to make place for the new. It was still under the impression left by the great earthquake of Lisbon in 1755 that the metaphors of earthquake arouse - a local event hat could affect an entire continent.

"Many parts of Europe are in obvious disorder. In many others there is a dull rumble coming from underground, a faint movement is felt that threatens the political world like a general earthquake."
Edmund Blurke (Irish philosopher, 1729-1797)

The picture of the volcano as positive symbol of insurrection against social injustice needed more time to become popular. Despite travel accounts and pamphlets, an erupting volcano was a rare event in Central Europe and mostly unknown to the larger public. In contrasts the popular tumult in Naples of 1647 was promptly compared to a volcanic eruption by the contemporary chronicles.

The use in the French language of the general term "éruption" during the French Revolution, meaning all kinds of release, from buds releasing their flower to realising own feelings or anger, became connected with the general comparison of the revolution to a purifying fire - it was then a short step to use the volcano to depict the enraged population:

"In the Royal Palace the most violent invocations followed with tremendous speed, the most violent orators jumped on the tables, inflamed the minds of their audience, which assembled around them, then to spread into the city like the burning lava of a volcano."
"Histoire de la Revolution de 1789 et de l´Establissement d´une Constitution en France." (1790)

Fig.1. "Third Eruption of the Revolutionary Volcano" (original caption "third eruption of the volcano of 1789, to take place before the end of the world, which will shake all thrones, and overturn a horde of monarchies") by Auguste Desperret (1804-65), lithography published in the magazine "La Caricature" of June 1833. Only after 1795 depictions of eruptions became commonly associated with social revolution (see also the volcanism blog for a further analysis of the image).

Bibliography:

THÜSEN, J.v.d. (2008) : Schönheit und Schrecken der Vulkane - Zur Kulturgeschichte des Vulkanismus. Wissenschaftliche Buchgesellschaft, Darmstadt: 239

The Last Virtuoso: Robert Hooke and his contributions in geology

"So, naturalists observe, a flea

Hath smaller that on him prey;
And these have smaller still to bite 'em;
And so proceed ad infinitum.
Thus every poet, in his kind,
Is bit by him that comes behind."
Jonathan Swift (1667-1745)

June 2, 1676 the Duke’s Company performed the spectacle “The Virtuoso” in the Dorset Garden Theatre in London. “The Virtuoso” was a comedy of great success, a tale about a strange philosopher – busy to explore, as he believed, the greatest secrets of nature: He measured the weight of nothing, used glowing mushrooms on putrefying flesh to read in the dark, tried to transfer blood between a sheep and a man to improve hair growth, taught spiders to dance and dissected a living dog.

The "silly science" and apparent nonsensical experiments caused great laughter in the public – only one man was not amused – Robert Hooke, Fellow of the Royal Society, architect, physicist, engineer, astronomer, but most important natural philosopher and the model for the buffoon on the stage. Hooke had in fact studied the weight of air, observed the decay and putrefaction of flesh and even how lungs work (in a living dog, an experiment he later will regret to have done).

Hooke was an acknowledged expert for the construction of scientific instruments, curator for experiments at the Royal Society and the first scholar to earn a living by research and applied science – or so he believed.

Born July 18, 1635, already in early years he became fascinated by the natural world. Hooke loved to search for fossils on the limestone cliffs of the Isle of Wigth (his birthplace) and already then the explanation of the time – fossils as products of a divine intervention- didn’t satisfy his curiosity.

In 1648 he went to London to study art, music and mathematics. He became a gifted engineer and constructed a sophisticated microscope and other tools to improve his senses – following the advice of philosopher of science Francis Bacon, Hooke believed that a man of science should trust only his senses to understand the natural world. It is this philosophy that pushes Hooke also to perpetuate experiments on topics the general public considers absurd.

In 1665 he published “Micrographia: or some Physilogical Descriptions of Minute Bodies made by magnifying Glasses with Observations and Inquiries thereupon“. In this work he not only depicts animals and plants observed under a microscope, but he discusses also questions regarding astronomy, physics, geology, volcanoes and fossils.

Fig.2. Ammonites as drawn by Robert Hooke himself and described in his “Discourses of Earthquakes and Subterraneous Eruptions”, published after his death in 1705. Hooke was a gifted illustrator and many fossils of his collection were drawn by himself to be included in his publications.

He was one of the first naturalists to see fossil forams. Having examined the calcareous shells with his microscope he compare this unknown animal with

“the shell of a small water-snail with a flat spiral shell: it had twelve wreathings […] all in proportion growing one less than another toward the middle or centre of the shell, where there was a very small round white spot.“

He observed also other striking similarities between petrifactions and living organisms. The similarities in the structure of charcoal and fossil wood (as we today know) convinced Hooke that fossils were the remains of once living organisms, however impregnated by “petrifying” fluids.


Fig.3. Comparison between plant cells, term adopted by Hooke himself, as seen in a piece of cork (above) and in a section of petrified wood (below), from Micrographia (1665).

The discovery of fossils on mountains, the remains of animals living once on the bottom of the sea (as demonstrated by the discovery of modern foraminifera in sediments dragged from the sea) proved an important fact - the distribution of land and sea, even the position of countries, was in a remote past very different to what we see today.


"There is no coin that can give such sure information to an archaeologist about the fact that there was a distinct kingdom ruled by a distinct prince, as these fossils give certainty to an natural archaeologist that these countries were once submerged, that there were these kinds of animals and that previously there were such changes and alterations in the surface of the earth [...] and these documents are written in more readable letters than the hieroglyphs of the ancient Egyptians, and on more durable material than the magnificent Egyptian pyramids and obelisks."

The changes of land and sea, the petrifaction of animals, even may their extinction (as many large ammonites, which he considered to belong or be similar to the genus Nautilus, were never found alive - "There have been many other Species of Creatures in former Ages, of which we can find none at present; and that 'tis not unlikely also but that there may be divers new kinds now, which have not been from the beginning.") were the results of natural forces. Hooke speculates in his "Discourses of Earthquakes and Subterraneous Eruptions", a collection of speeches delivered between 1667 and 1700 at the Royal Society and published in 1705, that earthquakes (however including in this term all kinds of movement of earth, even erosion and deposition) caused these changes.

"Most of those Inland Places […] are, or have been heretofore under the Water […] the Waters have been forced away from the Parts formerly covered, and many of those surfaces are now raised above the level of the Water's Surface many scores of Fathoms. It seems not improbable, that the tops of the highest and most considerable Mountains in the World have been under Water and that they themselves most probably seem to have been the Effects of some very great Earthquake."
 
Hooke doesn't publish much of his studies, always switching between topics he misses often to establish his priority. His publications are general and unspecific, he has many ideas, but follows few of them. Despite his genius, Hooke also had a hard-headed personality, especially in the last years of his live. He is envy of the success of others and likes to claim his priority in many fields, even when lacking publications or proofs of his research. It is this behaviour that will be especially mocked in "The Virtuoso".

Unfortunately Hooke dies in 1703, forgotten by society and the scientific community. His geological observations will be ignored for a century and later be overshadowed by Niels Stensen´s work. Natural philosophy is changing, first specialists, focussing on one topic per time, like the physicist Newton, are the emerging new heroes in the modern field of natural sciences.

"The preceding pages are far from giving an exhaustive account of the work of Hooke in geology. Quite like his contemporary Steno, he is one of these intellectual geniuses of the XIIth century who could be both rigid and visionary. Not at all mere "precursors", naive prophets, but authentic founders of our science. They deserve more than being glorified: we must read them. Only this honour is really worthy of them."
ELLENBERGER 1999

Bibliography:
DRAKE, E.T. (2007): The geological observations of Robert Hooke (1635-1703) on the Isle of Wigth. In WYSE JACKSON, P. N. (ed.) Four Centuries of Geological Travel: The Search for Knowledge on Foot, Bicycle, Sledge and Camel. Geological Society, London, Special Publications, 287: 19-30
ELLENBERGER, F. (1999): History of Geology: The great awakening and its first fruits, 1660-1810. Vol.2. Balkema Publishers, Brookfield: 409MESENHÖLLER, M. (2010): Das gescheiterte Genie. GEO 08/August: 77-88

Online Resources:

UCMP site - Evolution: Robert Hooke (1635-1703). (Accessed 21.02.2011).

A geologist riddle #5

An accurate, even wonderfull view on a small flea, but there was much more to discover at the time this engraving was made.

So there is a connection between this image of the flea and geology in general - what, or better - who is this connection?

AW#31 - Talus Thoughts

Jim Lehane on The Geology P.A.G.E. is asking the question "What geological concept or idea did you hear about that you had no notion of before (and likely surprised you in some way)."

Well I will admit that there is a problem that I come across only in geologically recent times and still puzzles me.

"Beautiful is what we see,
More beautiful is what we understand,
Most beautiful is what we do not comprehend."
Nicolaus Steno, 1673

Can a pile of rubble have e name and be studied? Apparently yes - a Talus (term used in North America, borrowed from the architecture of fortresses)) or Scree (English) can be defined as landform composed of rock debris accumulated by mass-wasting processes - or as pile of rubble. But despite this simple explanation, their humble origin, being often neglected during lectures or considered only disturbing in mapping the bedrock lithology, talus slopes are complex geomorphologic features still holding many secrets (not only to me).
These landforms occur in a wide range of environments, but most predominantly where the climate enforces on steep rock walls or cliffs physical weathering and mass-wasting. If the supplied rubble is enough, the subsequent weathering and removal rate low, a characteristic, thick cone or slope of rock debris can form. Rockfall is one important factor to form a talus; however depending on the catchment are other mass-wasting processes can act on the morphology of the talus, large rock avalanches can occur, debris flows, avalanches and dry grain flows also transport material on the developing slope.
These various processes can alter the form, the composition and the grain size found on the talus - so it is not easy (if possible) to foresee the inner matrix by only observing the surface. In most cases the coarse openwork surface texture is merely a veneer. Talus deposits consist of debris with a wide range of sizes, like a sieve, fine material accumulates in the voids in the deeper parts of the talus. Interestingly for me such a similar phenomenon has been observed also in rock glaciers and landslide deposits - I therefore experienced that is it tricky to map such features as simple aquifers.


Fig.1 and 2. More regular Talus slope / Talus aprons in the upper photo and cataclinal (bedding and slope coincide) slope with various Talus cones and modification by debris flows in the Dolomites.

Fig.3. Example of talus deposits reworked by debris flows (with the typical levees on the sides of the channel) in the Central Alps, area characterized by schists and metasediments. Physical and chemical erosion in such rocks is generally stronger, talus deposits tend therefore to be fine grained and covered by soil and vegetation.
Talus deposits are mainly results of mass-wasting processes, if fluvial ("wet") processes play also or a dominant role the term Talus fans is used.

The overall morphology of a talus slope depends also on the form of the cliffs supplying the debris. Straight plain cliffs will produce a straight sheet talus (Talus slope / Talus aprons), cliffs with channels or gorges will canalize the debris and Talus cones will form. It is mostly that both forms will occur in narrow spatial and temporal succession, a regular cliff will develop channels with ongoing erosion and faults can disrupt the regular conformation of a cliff.
Many talus slope profiles show at least segments with an inclination of 33-35°, a common value for rubble, however considering the entire slope there are significant variations. Mapped talus slopes show that the upper part has an angle of 32-37°, up to 40°, the medial part approaches the value of 33°, the lower part displays low angles and a basal concavity. The segmentation of the profile is in accordance to a change in the facies.
This shape is explained in part by various processes acting along the profile, in the upper part transport and deposition of debris, in the lower part mainly deposition. There is also a change in the grain size caused by "fall sorting": large boulders with their large momentum and energy proceed until the toe of the slope, also the roughness increases downhill, where older large boulders can stop the run of the new arriving boulder. The degree of sorting depends on the slope length, cliff height and the size and shape of dominant particles. This is an important effect of talus slope to be considered when defying a zone of danger or planning mitigation efforts.

Talus slopes in periglacial environments are again peculiar in some characteristics. A snow patch on the base of the slope and subsequent sliding of debris above this surface can produce a distinct ridge, termed protalus rampart or nivation ridge. Covering of snow by such debris is thought to produce an ice-rock mixture that can begin to creep following gravitational pull, a protalus lobe (often unfortunately also referred as protalus rampart), considered by me as one possible variation of rock glaciers.
When the ice melts out, unlike glaciers these lobes can not recede and became fossilised.

Fig.4. Complex talus deposits in the Antersac-Valley, Dolomites. The basal vegetation covered protalus rampart is a relict of a colder climate in a periglacial environment, probably during the aftermath of the last glacial period (18.000-12.000 years ago). Rockfall from the steep cliffs and canalized by a gully provide further debris, forming a talus cone, however the vegetation cover shows that the activity on it today is low. Most recent modifications are erosion of the upper part and secondary mobilization of material by various debris flows.

The coarse debris forming the talus can become preserved, and there is ongoing research to use these deposits to interfere the climate of the past. The presence of a Talus as such is not specific related to climate or environment, however the processes (avalanches, debris flows, grain flows) forming or modifying the Talus are depending on the climate.
Another possibility, despite recognizing the characteristic forms of ice-rock bearing talus slopes, is to try to calculate the accumulation of debris, and so the rate of weathering of the cliff. Assuming that a cold and wet climate increases debris production the ages of talus deposits can provide ages of such climatic phases. In talus slopes composed of carbonate rocks it is also possible to date directly the cement or the matrix formed between large boulders. Measuring the oxygen or carbon isotopes it is possible to recover direct climatic values.


These are only some considerations of many. Talus slopes are wonderful complex landforms, and being common in the region I work, they still continue to fascinate and intrigue me.

Bibliography:

LUCKMAN, B.H. (2006): Talus Slopes. In (ed): ELIAS, SA: Encyclopedia of quaternary science. Elsevier: 2242-2248