The Dolomite Mountains and the Dolomite Problem

Diedonnè-Silvain-Guy-Tancrede de Gvalet de Dolomieu, born June 23, 1750 in the village of Dolomieu, was a typical naturalist of his time. With 26 years he travelled trough half Europe, he got interested in the mines of the Bretagne and the basaltic plateau in Portugal, and he visited South Italy to study the aftermath of an earthquake in Sicily and observed an eruption of the Aetna.
In 1789 during a voyage to Italy with his student fellow Fleuriau de Bellevue he also travelled trough Tyrol. In the Brenner Pass area and between the cities of Bozen und Trento he noted a rock similar to limestone, but which showed no appreciable effervescences with acids. He published these observations in July 1791 in a letter to the "Journal of Physique".
Nicolas de Saussure, son of the Alpinist/naturalist Horace Benedict de Saussure requested some samples to analyze it. After some tentative denominations like "Tyrolit" or "Saussurit" in 1792 de Saussure published the "Analyse de la Dolomie" in the "Journal of Physique".
Even if the rock itself was not completely unknown, in fact called "Spat" or "Perlspat" by miners, it was not realized until the publication of Dolomieu that the rock was composed of a peculiar Ca-Mg carbonate. The Italian naturalist Giovanni Arduino (1713-1795) published in 1779 his observations about a peculiar limestone, found in the mountains surrounding Verona, but he didn't delve further into the subject and consider the idea of a new mineral.
So the name "Dolomite" became soon established, and in 1794 Richard Kirman introduced the Dolomite as a new mineral; the name from there became used to name the dolostone rocks and finally gave the Dolomites their actual name.

In the 19th century the genesis of both the Dolomite Mountains as the rock forming them became a major problem in geology. One of the most important achievements' was the recognition that the outstanding peaks and mountain groups are remains of ancient carbonate platforms and coral reefs.
In early days of geology less was known about the bottom of the sea and sedimentation occurring in oceans, only in 1842 Darwin formulated a first hypothesis dealing with the formations of tropic reefs.
Influenced by this model, intensive field mapping was carried out, and in 1860 the German geologist Ferdinand von Richthofen (1833-1905) recognised as first the Schlern Mountain as a slope of an ancient reef and other peaks as the remnants of large carbonate platforms.

Fig.2. In Leopold von Buch´s work "Esquisse d´une carte geologique de la parte meridionale du Tyrol" (1822) the author distinguishes carbonatic (light blue) from dolomitic rocks (dark blue).

After geologists could answer how the most spectacular rock walls and peaks in the Dolomites formed, the next urgent questions was if dolomite was a primary product of marine deposition or a secondary product of alteration of common limestone.

An insight to the problem came from the study of a characteristic geological formation in the Dolomites and its depositional environment: The appropriately denominated Hauptdolomit, the "main dolostone" formation, was defined in the Bavarian Alps by VON GUEMBEL 1857, and introduced in the stratigraphic nomenclature of the Alps in 1876 by LEPSIUS.

Fig.3. Example of Hauptdolomite forming steep rock walls, the Sass dla Crusc (Hl. Kreuz Kofel) 2.907m (with locals).

During the Upper Carnian and the Norian stage (216,5 - 203,6Ma) the Tethyan Sea experienced various regression and transgression phases.
The changing sea level resulted in the development of large water covered carbonate platforms or emerged tidal flats, on which a sequence of homogenous, meter thick carbonate muds with rare fossils (subtidal facies) and laminated bacterial mats and dolomite marls (peritidal facies) were deposited.
These deposits are widely distributed in the Eastern Alps, they can be found in the Southalpine unit (here denominated Hauptdolomit/Dolomia Principale Formation), as well as in a very similar development in the entire Austroalpine unit (Hauptdolomit-Gruppe in the Northern Calcareous Alps, Ortles nappe, S-charl nappe etc.) and in the Apennines and Dinarides, and therefore points at an enormous extension of this tidal sea.

During sea level low stand the muddy flats were colonized by algae and a species-poor faunal community, dominated by gastropods (Worthenia confabulate) and bivalves (Megalodus). Dinosaurs roved through the tidal flat, their tracks have been preserved at some locations. In times of emersion only thin mud layers were deposited by storms, which themselves were colonized by algae and bacterial mats, and which dried out repeatedly.

Fig.4. Detail of the Hauptdolomit - Formation showing algae / bacterial mats.

The extreme shallow water conditions continued uninterrupted throughout the whole Norian. The uniform and slow subsidence of the basement led to deposition of an up to 1.000 meters thick succession of homogeneous cycles of the two facies.
The top of the Hauptdolomite, and the end of the platform succession, is characterized by the development of polycyclic paleosols up to 30m thick, reflecting a major eustatic sea-level fall. One of the most intriguing differences of the Southalpine Hauptdolomite to other corresponding formations is the lack of intraplattform basins, with a succession of dark dolo- and limestone's, found for example in Lombardy and Austria. This fact is explained by missing tectonic activity during the Triassic in the area of the future Dolomite-mountains.

With this proposed reconstruction, geologists tried to find an actual and comparable environment to understand the deposition of dolostone: the large carbonate platform of the Bahamas Bank seemed to fit perfectly the prerequisites: a vast area covered with a shallow, tropical sea, with sparse islands and coral reefs surrounded by large tidal flats - there was only on problem: no or only a limited formation of dolomite is today observed in this environment.

The Dolomite Problem was still unsolved.

To be continued…

Bibliography:

BERRA, F.; JADOUL, F. & ANELLI, A. (2010): Environmental control on the end of the Dolomia Principale/Hauptdolomit depositional system in the central Alps: Coupling sea-level and climate changes. Palaeogeography, Palaeoclimatology, Palaeoecology 290: 138-150
BOSELLINI, A.; GIANOLLA, P. & STEFANI, M. (2003): Geology of the Dolomites. Episodes, Vol. 26(3): 181-185
CITA, M.B.; ABBATE, E.; ALDIIGHIERI, B.; BALINI, M.; CONTI, M.A.; FALORINI, P.; GERMANI, D.; GROPPELLI, G.; MANETTI, P. & PETTI, F.M. (ed) (2005): Catalogo delle formazioni. Unità tradizionali, Carta Geologica d'Italia 1:50.000, Quaderni serie III, Volume 7, Fascicolo VI: 318
LEPSIUS R. (1876) - Einteilung der alpinen Trias und ihr Verhaltnis zur Ausseralpinen. N. Jahrb. Min. Geol. Paleont.: 742- 744, Stuttgart.
NITTEL, P. (2006): Beiträge zur Stratigraphie und Mikropaläontologie der Mitteltrias der Innsbrucker Nordkette (Nördliche Kalkalpen, Austria). geo.Alp, Vol.3: 93-145
STEFANI, M.; FURIN, S. & GIANOLLA, P. (2010): The changing climate framework and depositional dynamics of Triassic carbonate platforms from the Dolomites. Palaeogeography, Palaeoclimatology, Palaeoecology 290: 43-57
VonGUEMBEL C.W. (1857): Untersuchungen in den bayerischen Alpen zwischen Isar und Salzach. Jahrb. K. K. Geol. Reichsanst., Jahrg. 7, H. I.: 146- 151, Wien.

30 August, 1965: The Allalin glacier Avalanche

The Allalin Glacier is a temperate glacier in the Vallese Alps (Switzerland). In the last centuries it became feared by its repeated advances and damming up of a melt water lake, which subsequently caused catastrophic outbursts floods.
At the end of the 19th century the glacier began to retreat, and during the first half of the 20th century the frontal part of the glacier tongue rested on the brink of a steep (27°) bedrock slope.

To prevent future inundations and to store the discharge of the glacier and use it to for a hydroelectric power plant, in 1964 the realization of a dam below the glacier fore field was decided. The construction works for the Mattmark dam began in 1965.

Some days before August 30, 1965 small ice blocks were observed falling down the slope, but this was not unusual.
On August 30. 1965, without warning, a major portion of the terminus of the glacier broke of, sliced down the rock slope and impacted on the huts of the construction site, 88 peoples working and living there were killed.

Fig.1. The Allalin Glacier before the ice avalanche, with marked glacier terminus part that caused the catastrophe, on the left corner the huts of the construction site (figure from HÖFLER & WITT 2010).

Subsequent investigations showed that the glacier avalanche occurred during a period of rapid advance of the glacier that started 2-3 weeks earlier, and pushed the front over a terrace in the bedrock. The glacier terminus slipped just on the margin of the steep slope, and became hold in place only by the connection to the glacier tongue. Finally the connection break off, the volume of the resulting ice avalanche was estimated to 1 million m3, and extraordinary and devastating event.

Similar seasonal changes in speed have also been observed in the years after the catastrophe, and it is now known that Allalin Glacier speeds up regularly every 1-3 years, usually during summer or late autumn. The acceleration is attributed to enhanced sliding, forced by the abundance of melt water, the different accumulation of ice masses by differences in the bedrock friction and the fragmentation of the glacier ice during the warm season.
In most cases however no large release of ice happens; evidently the speed-up event is necessary but not sufficient to cause breaking off. It is likely that geomorphologic factors, like the glacier bed topograpphy and a critical mass distribution inside the glacier, also contributed to the Mattmark catastrophe.

After the catastrophe a monitoring project of the Allalin Glacier was initialized. In 1999 the glacier configuration was similar to 1965, and for security reasons the hazard zone was closed during summer. An ice volume of 160.000 cubcic meters did in fact fell of, but did not cause any damage.

Despite the successful predictions in case of the Allalin Glacier, the mechanisms and relationships between glacier acceleration and break-off of large ice masses remain unclear, some steep glacier tongues switch between active and inactive phases, but other glacier tongues despite similar morphological conformations do not (for example the Giétroz Glacier in south-western Switzerland).

Fig. 2. Profile showing historical retreat of Allalin Glacier, Switzerland, and source of the 1965 glacier avalanche. The avalanche killed 88 construction workers at the Mattmark Dam construction site in the Saas valley (from EVANS & CLAGUE 1994).

Bibliography:

EVANS, S.G. & CLAGUE, J.J. (1994): Recent climatic change and catastrophic geomorphic processes in mountain environments. Geomorphology 10: 107-128
HÖFLER, H. & WITT, G. (2010): Katastrophen am Berg - Tragödien der Alpingeschichte. Bruckmann Verlag: 144

The Geo- Files:The unearthly cases in Geology: Ice from the Sky

Like in every other science also in geology there are presumed mysterious, unexplainable cases or artefacts - but most of these cases consists only of a collection of anecdotes or are simply retold without sceptic inquiry, but sometimes behind stories there are some interesting facts.

April 27. 2010 at 10.17 in the German village of Hettstadt (near the city of Würzburg): an ice block, 50 kilogram heavy, felt from the clear sky, breaking off branches of shrubs, damaging a pavement slab and excavating three craters, the largest 22 centimetre deep.
Such "megacryometeors" findings are reported from around the world, Jesús Martínez-Frías, researcher on the Centre for Astrobiology in Madrid, has documented 76 such impacts since 2002. One of the largest of these specimens is a presumed 400 kilogram block crashed in the Spanish city of Toledo in 2004.

Fig.1. (A) Megacryometeor in situ that fell in La Milana, Soria (27 January 2002). It landed near a startled farmer who was riding his tractor. More than 16 kg of ice was recovered by the environmental police of the Guardia Civil (Seprona). The size of the small impact crater generated by the megacryometeor was ca. 50 cm.
(B) One of the fragments of the megacryometeor that fell in San Feliz de Lena (Asturias) (26 January 2000) (artificial illumination to highlight its textural features), from MARTINEZ-FRIAS 2006.

The origin of the ice block remained a mystery, speculation about giant hailstones, defect airplane toilettes, ice meteorites and even terroristic attacks emerged.

The German Meteor however was analyzed by the meteorologist Frank Böttcher (Instituts für Wetter- und Klimakommunikation - IWK, a private company).
The chemical composition of the specimen of Hettstadt showed no differences to rain, the ice therefore was formed in the atmosphere, and is not of extraterrestrial origin. The lack of traces of human urine, disinfection solutions or other artificial chemical components also excludes the provenance of the water from an airplane toilette or an elaborated fraud.

The airspace of the village in the morning of the event was over flown by two airplanes in an elevation of 10.730m and 11.890m, calculating the time for the block to reach the surface, and considering the direction of the impact (deduced from the form of the impact crater and the broken branches) Böttcher showed that it is possible that the ice came from the location of one of the airplanes.
It's not unusual that ice forms by condensing vapour on wings of airplanes, also it is possible that blocks large enough reach the surface. The origin of ice from the hull of planes will probably explain the majority of reported cases of ice - "meteors", maybe also a in part misleading name for a terrestrial phenomena.

Nevertheless it´s seems that not all cases can be explained by ice coming from airplanes, Martínez-Frías in his archive collected reports of ice felt from the sky in the first half of the 19th century, when planes didn't exist; also some recent cases of ice blocks do not correlate with planes passing by the site of discovery.
At least a part of the ice chunks must have a natural origin without planes interference , possibly like hailstones strong air currents hold them floating until the weight is to great and they crash onto earth.

Bibliography:

MARTINEZ-FRIAS. J. & HUERTAS, A.D. (2006): Megacryometeors: Distribution on Earth and Current Research. AMBIO: A Journal of the Human Environment 35(6): 314-316

Online Resources:

BOJANOWSKI, A. (23.08.2010): Einschlag bei Würzburg: Forscher löst Rätsel der fliegenden Eisbombe. (Accessed 27.08.2010)
MARTINEZ-FRIAS, J. (2000-2010): Megacryometeors - Extreme atmospheric events. (Accessed 27.08.2010)

August 27, 1883: Krakatoa - The day the world exploded

"Perhaps, however, the most important evidence of what was actually going on at Krakatoa during the crisis of the eruption is that derived from witnesses on board ships which sailed between Java and Sumatra while the great outburst was in progress, or those that were at the time in the immediate vicinity of either the eastern or western entrance of the Sunda Strait. From many more distant points, however, valuable confirmatory or supplementary evidence has been obtained, for which we are indebted to the captains or passengers of vessels passing through the eastern seas during that period. Only three European ships appear to have actually within the Sunda Strait during the heigth of the eruption on the night of the 26th August and the early morning of the 27th, and to have escaped destruction, so that those on board could tell the tale of what they witnessed. " (SYMONS 1888, pag.15)

Fig.1. Ship routes and -positions 27. Agust 1883 (Topographic Map from Wikipedia, Ship positions from SYMONS 1888).

When the Batavian steamship "Gouverneur-General Loudon", under the command of T.H. Lindeman, approached the harbour of Anyer at ca. 14.00 o'clock August 26. 1883, the first explosion was reported, with a white cloud rising above the volcano and the sea, which showed a strange behaviour: the sea level was rising and falling in an irregular pattern. The city of Anyer was soon covered by a white to dark described cloud, blocking the sun and causing darkness. At 14.45 the Loudon full of passengers started their voyage to the 65 kilometers distant Telukbetung in Sumatra. Commandant Lindeman tried to remain as much possible to the east of the exploding island, to avoid the ash and pumice rain:

"Monday, August 27th. Finding that at midnight on the evening of our arrival [Aug. 26, 7:30 p.m.] there was still no boat come off to us from the shore, and as the weather was now much calmer, I sent the first mate in the gig with a crew of six men to find out what was the reason of this.
About 1 a.m. he returned, and stated that it had been impossible to land on account of the heavy current and surf; also that the harbour pier-head stood partly under water. The Government steamer Berouw, which lay anchored near the pier-head, hailed the mate as he was returning on board, and the people on board her then stated to him that it was impossible to land anywhere, and that a boat which had put off from the shore had already been wrecked.
That by 6 p.m. on Sunday evening it had already begun to be stormy, and that the stormy weather had been accompanied by a current which swept round and round (apparently a sort of whirlpool). When the mate had come on board, we resolved to await daylight before taking any further steps; however, for the sake of security, we steamed several ships' lengths outwards, because the sound of a ship's bell which seemed to be approaching us made us suspect that the ship must be adrift, and wishing therefore to avoid a collision we re-anchored in nine fathoms with thirty fathoms shackle outside the hawsepipe.
We kept the ordinary sea-watch, and afterwards heard nothing more of the bell. When day broke, it appeared to us to be still a matter of danger to send a boat ashore; and we also discovered that a revenue cutter was foul of a sailing-vessel which lay in the roadstead, and that the Berouw was stranded. However, owing to the violent winds and currents, we did not dare to send a boat to her assistance.
About 7 a.m. we saw some very high seas, presumably an upheaval of the sea, approaching us up the roadstead. These seas poured themselves out upon the shore and flowed inland, so that we presumed that the inhabitants who dwelt near the shore must be drowned. The signal beacon was altogether carried away, and the Berouw then lay high upon the shore among the cocoanut trees. Also the revenue cutter lay aground, and some native boats which had been lying in the neighborhood at anchor were no more to be seen.

Since it was very dangerous to stay where we were, and since if we stayed we could render no assistance, we concluded to proceed to Anjer under steam, and there to give information of what had taken place, weighed anchor at 7:30 a.m., and following the direction of the bay steered thereupon southwards.
At 10 a.m. we were obliged to come to anchor in the bay in 15 fathoms [27,5m] of water because the ash rain kept continually growing thicker and thicker, and pumice-stone also began to be rained, of which some pieces were several inches thick.
The air grew steadily darker and darker, and at 10:30 a.m. we were in total darkness, just the same as on a very dark night. The wind was from the west-ward, and began to increase till it reached the force of a hurricane.
So we let down both anchors and kept the screw turning slowly at half speed in order to ride over the terribly high seas which kept suddenly striking us presumably in consequence of a "sea quake," and made us dread being buried under them. Awnings and curtains from forward right up the main-mast, three boat covers, and the uppermost awning of the quarter deck were blown away in a moment. Some objects on desk which had been lashed got loose and were carried overboard; the upper deck hatchways and those on the main deck were closed tightly, and the passengers for the most part were sent below.
Heavy storms.
The lightning struck the mainmast conductor six or seven times, but no damage. The rain of pumice-stones changed to a violent mud rain, and this mud rain was so heavy that in the space of ten minutes the mud lay half a foot deep. Kept steaming with the head of the ship as far as possible seawards for half an hour when the sea began to abate, and at noon the wind dropped away entirely. Then we stopped the engine. The darkness however remained as before, as did also the mud rain." (from VanSANDICK)

The ash rain and the Tsunami as experienced on the Loudon, dramatization from the BBC docu-drama, "Krakatoa: The Last Days.":





Captain Thomson of the Medea, anchoring 130 kilometers east of Batavia, later estimated the height of the cloud up to 27 kilometers, he also reports "electric signs" in the clouds and strong explosions shaking in short intervals the ship.
At Monday at 5 o'clock in the morning three ships were still on the sea in the narrowest part of the Sunda Strait, the Loudon, incapable to reach Telukbetung because of the rough sea, the Marie and the Charles Bal. All three ships were covered by hot ash and pumice.
Captain Lindeman decided to anchor in the Lampung bay, also the Danish merchant Marie stopped. The Irish merchant Charles Bal, under the commando of captain W.J. Watson, in a desperate attempt to find a way out of the dark cloud approached the island of Krakatoa up to 16 to 18 kilometers, the nearest position of all surviving testimonies.
At Sunday 13.30 he was approaching the island in the middle of the strait (Watson reported the time 1 hour to early, here the indications are corrected to match the general chronology):

"…we observed a strong movement at the peak of Krakatoa, clouds or something were being propelled from the nort-east point with great velocity.
At 14.30 we heard about us and around the island a strange noise, like a crackling fire or the heavy artillery firing every few seconds. At four o'clock there was still thundering and it become even stronger, and a gloom spread over the sky, and a hail of pumice crackled on us, many of the pieces were of notable size and quite hot. We had to cover the lights, to secure the glass, and had to protect our feet's and heads with boots and coats.
..we remained on that course until we sighted a lighthouse at 18 o'clock, which we thought was Fourth Point, then we turned into the wind, SW, because we could hardly see anything and did not know what was going on in the strait.
The night was terrible, sand and rocks fell on us and made us blind. About us and around us there was absolute darkness, broken only by the incessant flashing of lightning, and then the constant noise of the explosion of the Krakatoa - our situation was really bad.
By 22 o'clock an island became visible. Fire tails seemed to descend up and down between it and the sky, and in the southwest we saw rise steadily white balls of fire.
The wind was strong, but hot, suffocating and sulphurous, it smelled like charred ash, and some of the stones that felt on us, were like iron slag. The plumbline coming from a depth of thirty fathoms [55m] was still warm.
From midnight to 3 o'clock in the night of the 27th the same impenetrable darkness persisted, while the noise of Krakatoa sounded less continuously, but more explosive, the sky was dark black in a second, and in the next bright light. The masts and frames flickered in a dead fire, and a strange pink-colored flame spout out of fluffy clouds, seeming to touch the mast.
At 5 o'clock we recognized the coast of Java, set sail and passed the lighthouse of Fourth Point. At 7 o'clock we winded up our signal flags, but received no answer.
At 7.30 we passed Anyer, our name still set and close enough to see the houses, but could see nothing moving, in fact across the entire Sunda Strait we saw nothing on the sea or on the land moving.
At 9.15 we passed Button Island, distant a quarter to half a mile, all around the sea like glass, and the weather looked much better, here no ash or slag was falling down, weak wind from SE.
At 10.15 o'clock we heard a terrible explosion in the direction of the Krakataoa, now more than 30 miles distant. We saw a wave impacting on Button Iceland and apparently sweeping across the southern part ...
... at 10.30 we were surrounded by a darkness that was almost to grasp, and then a deluge of mud, sand, and I do not know what began.
... We placed two men on the lookout, the mate and second mate on the flanks, and a man washed the dirt from the compass. We had seen two ships to the N and NW, before the sky darkened, so our situation was becoming even dangerous.
By noon it was so dark, that we had to grope on the deck, we could speak, but not see each other. This terrible condition and the rain of mud and debris continued until 12:30 o´clock. The thunder and lightning of the volcano was something awful.
At 13 o'clock we could see some of the yards above us, and the mud rain stopped, at 16 o'clock northwards and eastwards the horizon appeared, and we recognized West Island in direction O to N, just barely visible.
By midnight the sky remained gloomy and cloudy; occasionally some sand came down, the volcano rumbled in the distance, even though we were 75 miles distant from Krakatoa. Such darkness and such a situation only a few can ever imagine, and probably many would consider it unthinkable. The ship seemed cemented from the knob of the flag to the water line: spars, sails, blocks and ropes were terribly dirty, but Thank God no one was injured and the ship undamaged.
But imagine Anyer, Merak, and other small villages on the coast of Java!"

Bibliography:

SYMONS, G.J. (1888): The Eruption of Krakatoa, and subsequent phenomena. Report of the Krakatoa Committee of the Royal Society. Trübner & Co., London.
WINCHESTER, S. (2003): Krakatoa - Der Tag, an dem die Welt zerbrach. Albrecht Knaus Verlag: 367

Online Resources:

BBC World Witness (27.08.2010): Witness talks by Simon Winchester. (Accessed 27.08.2010)
LINDEMAN, J. (1883): Summary of Events. (Accessed 27.08.2010)
VanSANDICK: Krakatau/Krakatoa/Krakatou - 120e Verjaardag. (Accessed 27.08.2010)

Outburst flood from Glacier de Tete Rousse: A past and future threat

To protect the 3.000 inhabitants of the France village of Saint-Gervais–Le Fayet from a possible glacier outburst, the authorities have decided to drill into and install pumps on the Glacier de Tête-Rousse (Mont Blanc Massif), where a larger volume (65.000 cubic meters) of stagnant water is presumed. A supraglacial lake containing estimated 25.000 cubic meters water was discovered during this March, the authorities now fear that the water could be released in a sudden outburst when the surrounding icewalls collapse or the water excavates an outlet. In the course of this week the base camp at 3.200m a.s.l will be prepared, the drilling and installing of the pumps will presumably be concluded until October, before the onset of the winter.

Meanwhile the residents of the villages were warned of the possible danger and a evacuation plan is in elaboration.
The precautions are not entirely unfounded; in the night between July 11. and 12., 1892 the village of Saint-Gervais was severely damaged and 175 peoples killed by a 200.000 cubic meters outburst coming from the Tête-Rousse Glacier.
In the Alps, outburst floods from intraglacial cavities are not rare but generally lead to only small discharges and debris flows causing little or no damage. The outburst flood from Tête-Rousse was, however, one of the deadliest disasters ever caused by a glacier.

Before 1878, in a period with increased rate of ablation, a supraglacial lake formed in the centre of the glacier, this lake subsequently became covered by ice and snow.
The collapse of the glacier tongue in 1892 finally released the accumulated water, a large cavity 40m in diameter and 20m high containing estimated 20.000 cubic meters water at the glacier terminus remained as testimony. From this lower cavity, an 85m long intraglacial conduit led to the upper cavity (the former lake) with an additional volume of 80.000 cubic meters.

Fig. 1. The lower cavity at the terminus of the glacier, note epeople for scale. A part of the snout has been torn from the glacier. Photograph by H. PELLOUX, September 1892, figure from VINCENT et al. 2010.

Fig. 2. The upper cavity (former supraglacial lake) at the centre of the glacier. Photograph by M. KUSS, 13 August 1893, figure from VINCENT et al. 2010.

Fig. 3. Longitudinal section of the tongue, sketch from VALLOT and others (1892), figure from VINCENT et al. 2010.

After the catastrophe a monitoring program was initialized and in 1898-1899 a horizontal tunnel drilled to prevent water accumulation inside the glacier. In 1901, a 50m long and 40m deep crevasse became filled with water, so until 1904 a new tunnel was constructed, and 22.000 cubic meter water drained. This tunnel still exists and is supposed to prevent water accumulation close to the bedrock of the glacier.

Fig. 4. Map of surface and bedrock topography in 2007. The locations of the upper cavity and lower cavity (green dashed curve) and the excavated tunnels 81899 and 1904) are shown.

References:

VINCENT, C.; GARAMBOIS, S.; THIBERT, E; LEFEBVRE, E.; LeMEUR, E. & SIX, D. (2010): Origin of the outburst flood from Glacier de Tète Rousse in 1892 (Mont Blanc area, France). Journal of Glaciology, Vol. 56(198): 688 - 698

August 24, 79: The last day of Pompeii

"The last day of Pompeii", painted between 1830 and 1833 by K.P. Bruelow, State Russian Museum, Saint Petersburg. I posted about the taphonomy of the volcanic eruption of the Vesuvius here. There exists also an reconstruction of the eruption phase in form of a documentary by the Discovery Channel.

Botany for geologists: Lichenometry

Maybe one of the first naturalists to adopt botany on a geological dating problem was the English ambassador in Naples: Lord William Hamilton (1730-1803). Hamilton used the density and kind of vegetation cover to interfere the age of lava flows of Vesuvius.

Today a similar approach is used in lichenometry.
The idea to use the growth of lichens as simply and in field applicable method for relative dating of surfaces was first proposed by the botanist Knut Faegri in the 1930s, and in the 1950s developed further by the Austrian botanist Roland Beschel. During lichenological research on cemeteries he noted that on older gravestones larger lichens can be found. Many of the observed species where also found on rocks exposed by receding glaciers, Beschel realized that lichens could be used to relative date the glacial extensions in the Alps during the Holocene.
Despite the first promising results of lichenometry by botanists and geographers, geologists discovered the use of lichens in alpine or arctic environments only in the decade between 1960 and 1970, since then lichenometry was and is used as a simple field method to date moraines, rockfall deposits, debris flows, denudated rockwalls, escarpments and raised beaches.

Lichens are a symbiotic live community between algae and fungi. The microscopic alga furnishes nutrients for the fungus, the macroscopic visible fungus provide moisture and shelter for the alga. This partnership enables the two partners to colonize habitats, which the single organism couldn't possibly colonize by itself, and in fact as pioneer species lichens colonize an extraordinary variety of habitats and surfaces: Lichens can be found on debris and rock walls to an elevation of 7400m a.s.l., they grow on stems and branches of trees from the tropical to temperate forests, they can be found on rocks in the polar and equatorial deserts, and they colonize the boulders on shores of the sea.

The characteristic growth form or thallus of a lichen species is determinated by the fungus. Lichens growth forms can be divided into three groups based on the shape of the thallus:

- the fruiticose type consists of small tubules and/or branches,

Fig.1. Different Cladonia types.

- the foliose type shows a leaf-like thallus,

Fig.2. Umbilicaria sp.

- and the crustose type develops a flattened thallus overgrowing a surface.

Fig.3. A lichen community on crystalline rock - with a prominent specimen of Rhizocarpon geographicum agg.

This last group comprises the most common members of the lichens, and can be found extensively on almost all hard surfaces, like rocks, tree bark and artificial surfaces from buildings and gravestones. Most species however show a preference for a specific substrate, there are for examples differences in the species richness and assemblage found on carbonate and siliceous rocks.

Considering that lichens like all organisms tend to grow and reproduce it is possible observing lichens to relative date a surface. Given similar rocks and climatic conditions, the larger the lichen colony, or denser or richer the lichen assemblage on the surface, the longer will be the time passed since the growth surface becomes exposed and colonized.
Estimating the absolute age of a material from the lichen growing on its exposed surface first requires the determination of the relationship between observed diameter and age of the individual lichen. After measuring lichens on surfaces of known age, for example by studying surfaces on historic buildings, gravestones or already dated geomorphic features, it is possible to determinate the growth rate and plot a growth curve that relates lichen diameters or surface area to time.
Finally it is possible to compare measurements of lichens on a surface of unknown age with the established grow rate, determinate the age of the thallus and interfering a minimal age for the overgrown surface.

Fig.4. Radially grown specimen of Brodoa intestiniformis.

The colonization and growth of a lichen proceeds in four different phases:

1) Surface got exposed and after a while colonized, this ecesis denominated period is not directly determinable with the lichenometric method, however filed-observations of freshly exposed rocks after glacier retreat shows a lag time of 5 to 100 years, depending on the environmental conditions

2) rapid, logarithmic growth of the thallus

3) the growth rate diminishes, and proceeds in a linear manner

4) When lichens grow old, the growth rate gradually declines until death.

Not all lichen species develop a long-lasting phase with relative constant growth; these species can not be used in lichenometry, also the growth rate depends directly from the studied species and the environmental conditions - the growth is influenced by local, and regional environmental factors, such as temperature, moisture, nutrients, day length and snow cover (the latter factors influencing directly photosynthesis of the algae).
To obtain comparable results in an ongoing study it is necessary to measure thalli of the same lichen species under similar conditions, for example choosing a specific species on similar exposed surfaces of stable boulders.
The photosynthetic productivity in lichens is very low compared to "higher" plants, less than 25% comparing the same photosynthetic active areas between lichens and common plants. This low productivity implies a low growth rate, but also an increased longevity. Some lichen species (like Rhizocarpon geographicum) are estimated to reach (under favourable conditions like in the cold and dry conditions of western Greenland) an age of 5.000 to 9.000 years, the theoretical upper limits of lichenometry. However because lichens colonies eventually grow together, and can no longer be measured individually, lichen as a dating tool are used in a range less than 500 years. Under optimal circumstances lichenometry can provide age accuracy with a margin of error of less than 5 years over the past 200 years.

There are also different approaches, how to measure the single lichens specimens.
One of the simplest and fastest methods is to measure the axis of the five largest individual specimen, more elaborated methods increase the number of measurements or vary the measured parameters, like the diameter of an inscribed circle, the surface area, or the outline length of the lichen. Statistic approaches of the data obtained by these different methods showed that they not influence to much the results; therefore the first mentioned method is one of the most popular and most used.

Lichenometry is considered a useful method applicable in an easy and quick way in the field; however there are limitations and some considerations must be mentioned.
For the fundamental principle of the method, the growth rate of a lichen species, it is necessary to find appropriate lichen colonized surfaces of known age. The surface and the single specimens that will be measured and dated must also fullfil some requirements. Not all surfaces are equal, snow cover, sunshine exposure can vary, selected boulders can be instable and their changes of position can influence the growth of lichens.
The large scale climatic factors must be considered during the selection of survey sites, different climatic conditions can it make impossible to use the same growth rate for different valleys, even if geographically they are adjacent.
Despite the restricted numbers of species used in lichenometry, the method at least implies a basic knowledge of the lichen species and their classification. Some lichen species are very similar on a macroscopic scale and differ only slightly in colour or general growth pattern, also the colour of some species tends to change with age.
Despite the omnipresence of lichens, they are often neglected by non-botanists (and even botanists), good books on the matter for non specialists are rare, and important information's are often not divulged. For example one of the most used and well known lichen species by earth scientists, R. geographicum, according to botanist in fact is not a species, but an aggregate of different groups, with slightly different properties, resulting in possible implications on lichenometry not yet fully considered.

Despite these last considerations, lichenometry has proven to be an inexpensive, widely adaptable, and invaluable tool for use in estimating surface ages in lichen-dominated landscapes also for the geologist.

References:

McCARTHY, D.P. (2006): Lichenometry. 1399 - 1404 In (ed): ELIAS, S.A. (2006): Encyclopedia of quaternary science. Elsevier.
WALKER, M. (2005): Quaternary dating methods. Wiley Press: 304

August 21, 1986: The Lake Nyos catastrophe

The 21. August 1986 was market day in the village of Lower Nyos (Cameroon), from the surrounding mountains many herdsmen brought their livestock to do business with the local farmers. In the evening, at 21.30 p.m. most of the peasants and their guests were sleeping and didn’t notice the sound of an explosion coming from Lake Nyos, two kilometres distant to the village.

The few survivors report that their family members were eating, in the very next moment suddenly tumbled on the floor, death. A woman awaking the next morning found their five children dead in their hut. In Nyos that evening 1.700 people died. Rescue troops that arrived in the valley some days later reported of a sinisterly scene, villages with huts and gardens untouched, but everywhere bodies of humans and animals, there weren’t even insects on the corpses.The unseen killer was a 50m high cloud composed of 1,6 million tons of carbon dioxide, erupted from Lake Nyos and denser then the surrounding air following the valley for 27 kilometres, killing more then 1.700 people and 3.000 animals.

Fig.1. Lake Nyos as seen some days after the catastrophic release of carbon dioxide. It is thought that the violent degassing mobilized the lake sediments from the bottom and huge waves eroded part of the steep shores, bringing sediments in suspension and colouring the lake brown. On the border are various landslide scarps visible, it is possible that a landslide triggered the degassing of the lake (photo credit LOCKWOOD 1986).

Fig.2. Carcasses of animals as found some days later after the catastrophe, the bodies showed no injuries, the animals were asphyxiated by the carbon dioxide erupted from the lake (photo credit LOCKWOOD 1986).

This deadly phenomenon is explained by the geological position of Lake Nyos, situated in a volcanic caldera.
Calderas possess steep walls and cliffs delimiting it, so that if the Caldera becomes filled with water, the resulting lake is relatively deep. Because of their depth, these lakes show a strong temperature gradient between superficial and bottom water layers, resulting in different water densities. In temperate zones during summer the warmer and lighter water remains at the surface, preventing deep reaching currents and a mixing of the different layers. During spring and autumn the surface water cools, and sinks to the bottom. However in the tropics the constant warm climate during the entire year prevents this cooling, so that the bottom water becomes impoverished in oxygen and enriched in gasses emanating from the volcanic ground, mainly carbon dioxide, or created from the decomposition of organic material, mainly methane, for many years. This poisoned zone is called Monimolimnion. In a depth of 200m the water can so accumulate ten times more carbon dioxide then on the surface.

It’s not definitively known what finally triggered the lethal eruption of Nyos, it was speculated that an earthquake or submerged volcanic eruption disturbed the water stratification in the lake, enabling the accumulated carbon dioxide to escape its wet prison.
The days before August 21 were rainy; it is also possible that the rainfall cooled the superficial water layers so much, that an intermixing with the denser and poisonous water occurred.
A fourth possibility, supported by the observations of various landslide scarps on the shores of the lakes, is that a landslide triggered by the rainfall felt in the lake, disrupting the layering of the water column, and so eliminating the “cap” that prevented the carbon dioxide bubbling out from the gas rich bottom water.

The particular settings necessary for poisonous lakes, resulting from their geographic, climatic and geological circumstances, is known for only three lakes. Lake Nyos and Lake Manoun located in Cameroon, and Lake Kivu located at the border of Ruanda and Congo.
On August 15 1984 an explosion, probably caused by the release of gases, at Lake Manoun killed 37 people.

At Kivu, with his densely populated shores, the concentration of lethal gases, in part of volcanic, in part of bacterial origin, in a depth of 500m is extraordinarily. If an event like at Nyos happened, the live of hundred of thousands of people would be threatened. To prevent a natural and presumably catastrophic degassing of the lakes, in the last years the lakes are intensively monitored and the bottom water is brought to the surface under controlled conditions by tubes, where it can degas.

References:

DECKER, R. & DECKER, B. (1991): Mountains of Fire: The Nature of Volcanoes. Cambridge University Press. Cambridge: 243

Online Ressources:

LOCKWOOD, J. (1986): Oku Volcanic Field (Accessed 19.08.2010)

August 20, 1890: 120 years Lovecraftian Geology

“I am forced into speech because men of science have refused to follow my advice without knowing why. It is altogether against my will that I tell my reasons for opposing this contemplated invasion of the antarctic - with its vast fossil hunt and its wholesale boring and melting of the ancient ice caps. And I am the more reluctant because my warning may be in vain.”

The short extract is the introduction of "At the Mountains of Madness", a horror story by the American writer H. P. Lovecraft (born on 20. August 1890 in Providence) written in February/March 1931 and originally serialized in the February, March and April 1936 issues of Astounding Stories (one of the first pulp- and horror fiction magazines).

The story follows the tradition of the Cthulu-mythos - anyways presenting a more science (-fiction) approach to explain the rise and fall of the ancient god, and especially the elder ones. The story is written in first-person perspective by the geologist William Dyer, a professor from Miskatonic University (one of the institutions that possess a copy of the forbidden Necronomicon).

A geological Antarctica-expedition discovers first strange fossils, eons of years older then all other signs of life on our planet, and finally a mountain range, much higher and darker then the Himalaya in the remotest corner of this frozen world. But after a carefully investigation at the borders of the mountain range of more strange fossils, contact get lost with the team, and the narrator makes his way to discover what happened at the Mountains of Madness.

Lovecraft had a lifelong interest in the exploration of the Antarctic continent. The biographer S. T. Joshi notes, that "Lovecraft had been fascinated with the Antarctic continent since he was at least 12 years old, when he had written several small treatises on early Antarctic explorers.”

By the 1920s Antarctica was one of the last unexplored regions of the earth, where large stretches of territory had never seen the tread of human feet. Contemporary maps of the continent show a number of provocative blanks, and Lovecraft – as a writer- could exercise his imagination in filling them in. In fact the first expedition of Richard Evelyn Byrd took place in 1928-1930, the period just before the novella was written, and Lovecraft mentioned the explorer repeatedly in his letters, remarking at one point on "geologists of the Byrd expedition having found many fossils indicating a tropical past".

Lovecraft's was not only a passionate autodidact in geology, but also in American classic literature. Most obvious literary source for At the Mountains of Madness is Edgar Allan Poe's lone novel, The Narrative of Arthur Gordon Pym of Nantucket, whose concluding section is set in Antarctica. Lovecraft twice cites Poe's "disturbing and enigmatic" story in his text, and explicitly borrows the mysterious phrase "Tekeli-li" from Poe's work. Also, a graduate student, seeing at the arrival of the expedition on the McMurdo-Sund the active volcano Mt. Erebus, cites poetry by E.A. Poe to describe the scenery.

Many of the first Lovecraft's stories involve features that appear to be supernatural, such as monsters, demons and the occult, without clear explanation from where they come, or what they are. However, Mountains appears to explain the origins of such elements like the occult symbols or to "gods" such as Cthulhu in rational terms, by terrifying scientific facts - like the fossils, or inscriptions found on cyclopic walls of a sunken city. Mountains explains many elements of the "Cthulhu Mythos" and the origin of the crinoid-like very, very old elder ones .

Lovecraft with this story not only presents a weird tale, but also insights of the geological conceptions nearby 120 years ago - worth to be known by ever geologist to dare to approach the outer limits of geomadness.

Indonesia's Last Glacier

One of the strangest regions with glaciers can be found on the equatorial island of Indonesia, here on the mountain range of Pegunungan Maoke, emerging from the tropical jungle and with peaks reaching heights of 4.884m (Carstensz-Peak, conquered only in 1962 in the Puncak Jaya massif) still ice fields persists, but they are continuous shrinking.

Fig.1. Index map of Irian Jaya showing the location of the highest mountains, figure from ALLISON & PETERSON 2000.

A research team under the auspice of Dr. Lonnie Thompson, specialized on glaciers of the equatorial region, is actually trying to take as much ice cores as possible from the last persisting ice fields of the Carstensz-Peak.
All the “glaciers”, a terminus to be adopted only if the ice shows an active movement, otherwise the correct term is “ice fields”, have experienced a pronounced retreat in the last century, and the predominant rainy weather of the last years on the mountains is melting rapidly the remaining ice and warming the bedrock. So in 2003 the ice field of the 4.760m high Puncak-Mandala and the ice field of Puncak Trikora (4.730m) disappeared, and the last remaining glaciers of the oceanic realm, the North Wall Firn, the Meren Glacier, and Carstensz Glacier surrounding the Carstensz-Peak, experienced massive volume and surface loss (less then one square kilometre persists) and got fragmented in various inactive parts.

Fig.2. Oblique aerial photograph looking east at several of the glaciers on Puncak Jaya in 1936. Left to right: Northwall Firn, Meren Glacier, and Carstensz Glacier. Photograph from ALLISON & PETERSON 2000.

Fig.3. Oblique aerial photograph looking east at the glaciers in 1972. Photograph acquired during the Carstensz Glaciers Expeditions (CGE). Compare with figure 2. Photograph from ALLISON & PETERSON 2000.

The researchers were able to recuperate two 30m long ice cores which show an annual layering and will be studied to determinate the climatic variability of the region.

The ice-archive on the mountains of Indonesia's Papua Province are an important stratigraphic record for the climate at the border of the Pacific Ocean, one of the largest basins were thermic energy is stored in the sea or released to the atmosphere, influencing the climate on the whole planet.

Online Resources:

ALLISON, I & PETERSON, J.A. (28.04.2000): Satellite Image Atlas of glaciers of the World - GLACIERS OF IRIAN JAYA, INDONESIA. (Accessed 19.08.2010)
Ice Core Paleoclimatology Research Group (Accessed 19.08.2010)

Geology history in caricatures: A Coprolitic Vision

Approach, approach, ingenuous youth,

And learn this fundamental truth:
The noble science of Geology
is founded firmly in Coprology
P.B. Dunacn quoted in BUCKLAND, F. 1883

Cartoon drawn and published in the EARTH magazine by Callan Bentley, used here with kindly permission (thanks)

This post is a tentative submission to "The Carnal Carnival!"

Coprolites, from the Greek "kopros" and "litos", roughly translated into dung stone, can be regarded as a variety of ichnofossils (trace fossils), defined more precisely as fossilized, large biodepositional structures, documenting the presence, behaviour and physiology of an animal (PEMBERTON& FREY 1991).

The scientific term was introduced by the notorious eccentric, but also ingenious British Reverend William Buckland (1784-1856).
Buckland's interest in animal faeces arose from his studies on cave deposits and intermixed organic remains. In various caves that he visited, he noted scattered bones and white deposits, which he interpreted to be hyenas’ droppings preserved on the cave floor. To verify this hypothesis, he actually fed a spotted hyena from a travelling menagerie with ox bones, and on the next day compared the gnawed bones and the new available droppings with the old coprolites, concluding that there was "no difference between them, except in point of age" (BUCKLAND 1823).

Despite the modern approach and the astounding result - Buckland could demonstrate that the bone accumulations of caves where not caused by a biblical flood, the still proposed explanation of the time - his friend the chemist William Wollaston, who accepted to analyse the droppings (resulting of phosphatic composition, similar to the fossil ones) confessed to Buckland:

"though such matters may be instructive and therefore to a certain degree interesting, it may as well for you and me not to have the reputation of too frequently and to minutely examining faecal products."

In May 1829 Buckland began to write down the research on coprolites in some preliminary papers, in his final draft of the work published in 1835 he included his cave experiences and the research on the fossil faeces of Ichthyosaurus from the Lyme Regis area in Dorset, region he visited guided by the famous amateur fossil collector Mary Anning. Curious to note that until the study of Buckland the faeces fossils found at Lyme Regis were regarded as fossil fir cones.

“It has long been known to the collectors of fossils at Lyme Regis, that among the many curious remains in the lias of that shore, there are numerous bodies which have been called Bezoar stones, from their external resemblance to the concretions in the gall-bladder of the Bezoar goat, once so celebrated in medicine: I used to imagine them to be recent concretions of clay, such as are continually formed by the waves from clay on the present beach; but I have now before me sufficient evidence to show that they are coeval with the lias, and afford another example of the same curious and unexpected class of fossils with the album graecum which I first discovered in 1822 in the cave of Kirkdale, being the petrified faeces of Saurian animals, whose bones are so numerous in the same strata with themselves.” (BUCKLAND 1835)

Buckland, observing the narrow spatial context between the bones of the Ichthyosaurs, hyenas and the excrements coins even one of the first Ichnogenera, letting no doubt what he is referring at:

“I propose to assign the name Ichthyosauro-coprus to the fossil faeces which are thus evidently derived from ichthyosauri.” (BUCKLAND 1835)

“I need only refer to the account given in my Reliquiae Diluvianae, of the faeces of hyaenas in the Cave of Kirkdale, and to the large quantities of the same substance that have subsequently been discovered at Torquay and Maidstone, an din the Cave of Lunel, to show how frequent is the occurrence of Hyaeno-coprus in diluvial mud and gravel.” (BUCKLAND 1835)

Buckland adopted also in the liassic case his actualistic - comparative method to infer a possible behaviour of the extinct animals:

"Dispersed irregularly and abundantly throughout these petrified faeces are the scales, and occasionally the teeth and bones, of fishes, that seem to have passed undigested trough the bodies of the Saurians, just as the enamel of teeth and sometimes fragments of bone are found undigested both in recent and fossil album graecum of hyenas..[]..The bones are chiefly vertebrae of fishes and of small Ichthyosauri;...[]..still are sufficiently numerous to show that these monsters of the ancient deep, like many of their successors in our modern oceans, may have devoured the small and weaker individuals of their own species." (BUCKLAND 1835).

"The author concludes that he has established generally the curious fact, that, in formations of all ages, from the carboniferous limestone to the diluvium, the faeces of terrestrial and aquatic carnivorous animals have been preserved; and proposes to include them all under the generic name of Coprolite." (BUCKLAND 1835).

Fig.1. Copy of the plate illustrating coprolites of Tertiary Strata, from BUCKLAND 1835. Buckland fashioned a large collection of coprolites from the Lias of Lyme Regis, but also from Carboniferous and Tertiary strata. Some examples in this plate however are artificial ones, fabricated by Buckland to prove his argument. The ingenious Buckland filled the intestine of sharks and dog-fishes with cement, and later sectioned the animals to recover the resulting cast and compare them to the fossil ones.

Despite his scientific approach to the matter, Buckland (like in many other subjects) never take it and his research to serious. His Son, Frank Buckland, remembers:

"Some of these coprolites have been turned to purpose of art, under the name of "Beetle-stones". Dr. Buckland had a table in his drawing-room that was made entirely with these coprolites; . . and which was often much admired by persons who had not the least idea of what they were looking at." (BUCKLAND, F.T. 1883)

It’s seems obvious that contemporaries would make fun of this dedication to the art of coprology - and one of the most fitting cartoons regarding Bucklands’ passion comes from the geologist, and good friend of Buckland, Henry De la Beche.

Fig.2. De la Beche caricature "A Coprolitic Vision", lithograph print ca. 1829, image from here.

"Although he appreciated the value of his friend's scientific insights, De la Beche could not resist the temptation to caricature this "Coprolitic Vision". he produced a lithograph (ca. 1829) showing the "Reverend Professor of Mineralogy and the Geology in the University of Oxford", dressed in gown and mortar-board, and standing on a flat rock at the opening of a long cavern shaped like the nave of a cathedral. The columns supporting the roof where bloated spiral-shaped bezoars, and Buckland, with a geological hammer in his right hand, as it were conducts a service attended by animals - a deer, a bear, hyenas, a leopard, crocodiles, ichthyosaurs and pterodactyls. Every member of the choir and congregation are shown in the act of defecating. There are even large cylindrical shapes on the rock in the foreground, and one beneath Buckland's own legs." (McCartney 1977)

References:

BUCKLAND, F.T. (1883): Curiosities of Natural history. Second Series. Richard Bentley and Sons. London: 360
BUCKLAND, W. (1823): Reliquiae Diluvianae; or Observations on the Organic Remains Contained in caves, Fissures, and Diluvial Gravel, and on Other geological Phenomena, Attesting the Action of an Universal Deluge. John Murray. London: 303
BUCKLAND, W. (1829): Additional remarks on coprolites and fossil sepia. Proceedings of the Geological Society of London 11: 142-143
BUCKLAND, W. (1835): On the discovery of coprolites, or fossil faeces, in the Lias at Lyme Regis, and in other formations. Transactions of the Geological Society of London, second series 3: 223-236
McCARTNEY, P.J. (1977): Henry De la Beche: Observations on an Observer. Friends of the National Museum of Wales. Cardiff: 77
PEMBERTON, S.G. & FREY, R.W. (1991): History of Ichnology: William Buckland and his "Coprolitic Vision". Ichnos 1: 317-325