The greatest show on earth

No excuses more, because now you mustn´t even read: "The greatest show on earth: the Evidence for Evolution" by Dr. R. Dawkins as audiobook.

Picture by Darius Whiteplume's Tumblr.

The Permafrost Menace

The term permafrost is primarily associated with regions such as Alaska and Siberia, with a vegetation-free tundra, rock-hard frozen ground, and with the famous finds of well preserved carcasses of ice age mammals. But permafrost occurs in much wider geographic range, at least 23% of the Earth surface is influenced by permafrost.

Permanently frozen ground or permafrost is by definition material (bedrock or loose material), which remains at least for one year or two winters frozen, with temperatures below 0 ° C. Water, and so ice, is not necessary "needed" in permafrost, therefore called dry permafrost, but this kind of frozen ground plays geomorphological a minor role.

Climatic change has important effects on the distribution and the energy balance of permafrost , so influencing the amount of ice conservated in it. Permafrost occurence depends of various climatic (like temperature, insolation, precipitation and snowcover) and also from geomorphological (like exposition) and biological (like vegetation cover) factors - the role and interplaying between this factors is still poorly understand.
Permafrost in the middle latutudes lays only some degress under the melting point of water of 0°C, even a sligthly warming of the mean air temperature - and surface temperature, can heavily affect permafrost. The distribution diminuishes, and the depth of the active layer - the layer of permafrost that defrost´s during summer, increases.

How exactly permafrost reacts to the observed warming of 0,5°C during the last century in the Alps is still poorly known, and the exact mechanisms not understand. The strong retreat of glaciers is obvious, but permafrost was though to react much slower, because of the insolation effect of the covering debris layer. But observations of temperature profiles in drillholes showed that percoliating water, resulting from melting of more superficial ice, can "tranport" heat much faster in the underground.

Studying permafrost is a hard job, especially if it hides inside compact rock. PermaNet drill site in the valley of Schnals.

Morains and talus cones not only are habitats for specific, sometimes endemic animals and plants, but consists of loose debris hold together most time only by ice in the cavities between the boulders. Loosing permafrost can destabilise rock walls and debris, causing rockfalls and debris flows, and so putting infrastructures and humans life in danger. In the last 10 years the greatest rockfalls in the Swiss Alps occured in permafrost affected areas, one of the most spectacular in summer 2006 felt from the east-wall of the Eiger.

The rockfall of the Thurwieser mountain (3.652m, 46° 29` 45`` N, 10° 31` 28`` E) occurred on 19.09.2004 (first image befor, second after). 4,5 million cubic meters material felt on the underlying glacier and boulders up to 50 cubic meters slipped on it until 2000m a.s.l. The rockfall was caused probable by ice degradation.

The melting permafrost can influence the percolation and the paths that groundwater can take, so influencing springs. Observations in the european Alps and the Colorado Front Range showed also a change in the water chemistry in lakes and springs where permafrost features, like rock glaciers, occur in the catchement area. The change in water balance and presence can also effect the distribution of vegetation and the species richness of a habitat.

Hochjochferner 1891

The Hintereis -glacier (in the center of the picture), Hochjoch - glacier (left) and the Kesselwand - glacier, drawing by Schmetzer 1891. Position: 46°49`34``N, 10°50`20``E
"Aus den tiroler Alpen: Der Abschluß des Oetzthales mit dem Hochjochgletscher (links), dem Hintereisferner (in der Mitte) und dem Kesselwandferner (rechts oben). Nach der Natur grezeichnet von K. Schmetzer (1891)."

Accretionary Wedge #20: Why?

Asked for the ultimate answer to the Ultimate Question of Life, the Universe, and Everything, Deep thought, the supercomputer created by the imagination of the science-writer Douglas Adams, asked the far more important question: What is the ultimate question itself?

An wise man once said, a fool can ask more then ten men of science can possibly answer, but a problem and a good question is the first step of scientific research.
Geologist and earth scientists in the past centuries where observing rocks, relationships between them, superposition, unconformities and many other features, and came to ask themselves the apparent simple question: how came this marine limestone on the top of the mountain, why the coasts of the continents resembles the conjunctions of a gigantic jigsaw, where all rocks deposited by volcanic eruptions or sedimented in a quiet ocean basin? Today a part of these questions seems trivial, but still some of them are not conclusively answered. And even if we assume a question is answered, changing also slightly the problem can open the ways to a bunch of new issues.

In a survey carried out on 753 scientist from different nations around the globe , the german magazine "Spiegel" asked for the greatest - still unresolved problems in geosciences, and not so surprisingly the results fit quite well with the ultimate questions that trouble the Geoblogosphere:


Lockwood asks directly from Outside The Interzone one of the most important question from a slightly different perspective, not why earth enabled the existence of life, but why life enabled the existence of earth? Without life, this planet wouldn't be "Earth." Or we can ask ourselves, would nonexistings men be concerned about nonexisting earth?


Today Humans were concerned about Earth, especially when geological phenomena threaten their lives and their property - like volcanoes. It seems today elusive, that once volcanoes and their products where considered by earth scientists only as local features, with no significance for the geological evolution of earth - living in quiet central Europe they underestimated the power of this fire mountains - or asked they simply the wrong questions?

Not so Tuff Cookie, introducing us in the burning question how Magma reaches the surface of Earth, and how to study it´s path without X-ray powers and invulnerability. To understand the mechanism of volcanic eruptions may helps to predict and mitigate the impact on our society - a very important question with even more important answers.


And Hypo-theses proposes the ultimate hypothesis: With ongoing research we realized that earth is a complex systems, with factors like the interior structure, the outer crust, the liquid and the frozen hydro- and atmosphere and the biosphere (and humans) interacting among themselves, so ... what would be, if we really understand earth?


Many thanks to all participants for the content and the questions of this edition of the Accretionary Wedge. But don´t panic - at least one important question can be answered now - who is hosting the next Accretionary Wedge?

Lac du Bouchet

How Florian correctly answered, the WoGE was the maar lake of Bouchet and it´s very long stratigraphic sequence.

Located in the south eastern part of the French Massif Central, the volcanic region of Velay contains numerous maar craters. Pollen analysis has been carried out on lake sediment sequences obtained from three of these craters - Lac du Bouchet, Ribains and Praclaux. The presence of thick trachytic tephra layer has enabled correlations between the sequences. This has led to the reconstruction of a long continental sequence from 450ka ago to the present.

The attribution of the sequence to the last five climatic cycles is based on an apparently continuous succession of warm and cold phases, which correlates with the marine oxygen isotopic record. Tephra layers in the organic deposits of Lac du Bouchet provided Ar40/Ar39 dates with an average of 275ka - after this considerations the Lac du Bouchet temperate phase is correlated to the Marine Isotopic Stadium 7.


Lac du Bouchet (44°55´N, 3°47`E, 1.200m altitude) is a 28m deep lake, and has been the subject of numerous geological and biological studies. It yielded a sediment sequence extending from about 325ka to the present.


The Bouchet sequence can be subdivided by the amount of pollen taxa in three interstadials, which shows a classical succession of tree species, from cold tolerant at the beginning, to warm climate species, to again cold tolerant trees.


The proposed chronostratigraphy for the Velay maar sites (after REILLE et al. 2000, modified).

The Bouchet I interstadial is characterised by the presence of great quantities of Carpinus pollen, other thermophile taxa like Abies and Fagus are rare, or like Taxus complete missing. The Carpinus forest was probably the dominant vegetation everywhere in Velay at that time.
The Carpinus forest was then replaced directly by a Pinus forest, the latter marking the end of the interstadial and maybe a sudden cooling.
The Bouchet II interstadial shows similarities with the fist: again a Carpinus forest develops, but this time other trees like Ulmus, Corylus, Abies, Fagus and Picea must be also been present with significant numbers. As usual, the intestadial ends with a Pinus forest.
The third interstadial - Bouchet III, differs in significant taxa appearance and significance from the earlier two interstadials. Alnus viridis, today absent in the Massif Central region, but found as pioneer species in the timberline of the Alps, plays a mayor role in the first phase of the interstadial. This tree is then replaced by Ulmus, Quercus and Corylus, an Oak forest occasionally coexisting with a Picea forest develops. Carpinus this time doesn't form a forest of its own.

The establishment of tree taxa depends not only by the climatic conditions, but also from the distance of an investigated site from the glacial refugia of the species, and the capability of this species to spread. This maybe can explain the differences between the forest developments in the three interstadials.

The site of the ancient (with sediments filled) maar of Praclaux, in the vicinity of the Lac du Bouchet, today a quiet pasture.

References:

REILLE, M.; BEAULIEU DE J.L.; SVOBODA, H.; ANDRIEU-PONEL, V. & GOEURY, C. (2000): Pollen analytical biostratigraphy of the last five climatic cycles from a long continental sequence from the Velay region (Massif Central, France). Journal of Quaternary Science (7): 665-685

Where on Google Earth #173

The last excursion of WoGE (pronounced WvoGoEe) showed us some important type localities - locations where for the first time a mineral was found and described, or where it is found in accessible and well recognizable specimens - so the last round for example was the mineral "Tyrolensis" - no wait, was it "Saussurite", or should we name it "Arduinoite" ?

No - even if a first chemical observations of a strange Mg-rich limestone was published in 1779 by the Italian geologist Giovanni Arduino, the honour to became named a mineral in 1792, and then a mountain range after him, pertains to a restless "voyageur".
With 26 years - after some troubles with justice- he decided to travel and visited different geological localities of the European continent (a early Woge-Player?), so in 1784 he came to the Italian province of Calabria, after the great earthquake. And being there, he visited another well known geological phenomenon of the region on the great island nearby - even when then you couldn't go skiing on the top of this geological feature.

Remaining at home in his country he could also have visited Mg-bearing black rocks (this time not related to his name) and so the geological feature that he discovered active in Italy - even when these features today are filled with a complete opposite element to the strange things in Italy. And there finally it is , the WoGE 173, with 500m in diameter:


But that's good so, because if something fells in this hole, it remains there, and when after 325ka climatologist cam to drill, they sometimes discover another warm "climate" - and name it after the locality they found it - so at end, it's just another type locality.

I think from the first clues you can quickly deduce what country ´s geology you have to study to find the geological "spot" - it would be sufficient to name the general context of this point, maybe the specific content of the "holes" is known better to quaternary geologist - but if you really good (and I expect nothing lesser) you can also explain why the keyword here is "climate".

"For any new players to Where on (Google) Earth, simply post a comment with latitude and longitude (or a description of the location) and write something about what the features in the picture are, or how they have developed. Also you need to explain how the keyword fits in there. If you win, you get to host the next one - with the new twist to the game: the location should be connected to the previous one by some common concept, or “keyword”."

Schott's Rule could be applied: former winners have to wait 1 hour for each WoGE they got right.

Good luck !

debris flow calendar

The past weekend strong rainfalls caused various debris flows in my near surrounding area, with significant damages and one roadmen missing after a debris flow hit the street he was clearing from detritus.

To understand where and when these events hit is vital for appropriate response tactics and risk evaluation for urban areas. Thereby, the frequency and magnitude of debris flow events are of especial interest, also in view of climate change and human impact.
Information for past debris flow events in historic time can be obtained by studying archives or contemporaneous eyewitness reports/images. Prehistoric events can be reconstructed by 14C-dating of buried soils, dendrochronolgy or lichenometry. The disadvantage of these approaches is their limited time span and coarse resolution.

In the bottom sediments of the lake of Braies, in the Dolomite Alps, another possible long term record was, and still is, studied (IRMLER 2003; IRMLER et al. 2006). The lake Braies is an alpine lake on 1.492m a.s.l. with a maximum area of nearly 36ha and a catchment area of 30 square kilometres. It is surrounded by mountains up to 2.800m, dominated by dolo- and limestone formations. Several debris flow cones extend from the slopes of the mountains to the southern and eastern shores of lake Braies.

View to south with the main debris flow cones entering the lake Braies.

Simplified geological map of the lake and surrounding area (after IRMLER 2003).

In thin sections recovered from cores taken from the bottom lake sediments between annual laminations several "event layers", representing debris flows, were recognised.
Entering the lake, the debris flow brought more fine sediments in the lake then the average sedimentation rate of some millimetres per year. Under the microscope graduated layers, with progressive fining upward sequence, from well-sorted fine to middle sand at the base to silt and clay on the top could be recognized. Load casts and flame like structures support reconstructed rapid deposition. These structures indicate that the sediment moved as underflow (hyperpycnal flow - density current) into the lake basin.
A second category of layers lacked the above mentionetd characteristics, nevertheless these layers show a graduation and are much thicker than the surrounding lamination - up to seven times. These sediments are interpreted as deposits of overflow currents (hypopycnal or homopycnal flow).

Example of the studied core with recognizable annual lamination (from IRMLER 2003).

Erosive contact between annual lamination and a debris flow layer. The base of a debris flow layer is usually very coarse and the single grains more or less the same size.
Photo C) and D) shows so-called "flame structures" and small grooves - caused by the erosion of a debris flow event (Picture size ca 3.9 mm), from IRMLER 2003.

With this approach a debris flow calendar for the last 2250 years could be reconstructed. (IRMLER et al. 2006). During this time the recurrence interval of debris flows varies between 1 and 127 years. At an average of every 16 years a debris flow was deposited. The comparison with climatic phases, from the "Medieval Warm Period" to the "Little Ice Age" showed no significant correlation of events in the catchment area of lake Braies with climatic phases.
The study shows that lake sediments represent a good archive for reconstructing debris flows. In doing so, the record provides the possibility of estimation from the past the threat posed by natural hazards and gives important data for future hazard prediction assessment.

References:

IRMLER, R.; DAUT, G. & MÄUSBACHER, R. (2006): A debris flow calendar derived from sediments of lake Lago di Braies (N. Italy). Geomorphology 77:69-78
IRMLER (2003): Seesedimente als natürliches Archiv zur Erstellung eines Murkalenders am Beispiel des Pragser Wildsees (Norditalien). Ph.D. Thesis, University of Jena, Germany.

Glacier Erosion

Forms of glacial erosion represent some of the most widely distributed and recognizable indicators for past glacier extent. The discovery that polished rock surfaces were formed trough glacier abrasion, and the subsequent mapping of this feature on valley floors very distant from recent glaciers, was vital for the support of the "glacial theory" in the mid-1800s by the geological community.

The glacial striations of Le Landeron on Lake Biel, visited by the participants of the excursion of the Société Géologique in 1838, in a representation of Agassiz's work Etudes sur les glaciers of 1840.

Abrasion is the process of (frictional) wear, produced by surface rubbing against each other, and is achieved in the subglacial environment by sliding of debris-charged ice across the rock-bed.
Roches moutonées are the classical example of subglacial bedrock erosion, with abrasion dominating on the upstream (stoss) side and plucking (material pull off) on the lee side. This results in a highly unsymmetrical form, with a plain, upward side and a step to vertical termination.


To be continued...

Geologists Who Say "Nye"

Roches moutonnées of the last glacial maximum seen by the "Geotope Fischbach" (Bavaria) with Nye channels (after a British physicist) - subglacial channels eroded by meltwater under high pressure in the limestone formation of the "Wettersteinkalk".

In warm-based glaciers, also called temperate glaciers - with the bottom near or slightly above the freezing temperature, water flows in or on the bottom of the glacier forming subglacial streams in channels, that finally join at the snout, forming a glacier outlet.

There are three types of subglacial channels, depending on such factors like glacier movement, bedrock topography and lithology:

N-channel or Nye-channel: incised in the underlying bedrock.

R-channel or Röthlisberger-channel: incised in the ice (and so not found in "fossil" form).

C-channel or Clarke-channel: partly incised in the bedrock and ice, a combination of the formerly mentioned types.