Sonntag, 29. März 2009

Beaver Basins

Geologists normally doesn´t consider animals as a mayor factor in sculpturing earth surface and landscape – yes, there are exceptions, like corals that build up large reefs, but there what counts is number and time, not the single organism.

Single or periodically operating events causing geomorphological features and distinct sedimentary patterns are much more rappresented by a vulanic eruption or a landslide, yet even a storm or a flood, ... but mammals? But in fact, some animals can produce geomorphological response in a sedimentary or erosional system, not directly , but for example by damming up rivers.

The potential of beaver (Castor canadensis) damming to have a significant geomorphic impact on postglacial fluvial landscapes has long been suggested and used to explain observed broad, flat valley floors in the Colorado Front Range.

Sediment deposition measured in modern beaver ponds shows that aggradation of up to ~1 m is common within several years after damming, up to a maximum account of 2m, considered the medium high for a beaver dam, that can last up to 46 years.

Drained beaver pond in Allegany State Park (from Wikipedia)

Larger depositions are therefore considered representing various beaver-dam generations, but until now very few studies were focused on this possibility. Beaver dam abandonment often results in collapse of the dam, and new channel incision through accumulated pond sediments and upstream alluvium by the new formed river.

Beaver dams can exist only where there are beavers, so for example habitat preferences, food resources and competition control where beaver dams are built, and should thus influence the long-term geomorphic impact of beavers.
Geomorphic factors also strongly influence beaver dam distribution along mountain streams, to large or to steep river channels, or to strong curent limits the ability of the animals to maintain dams.

In a study conducted by PERSICO & MEYER in Yellowstone National Park, beaver dam deposits were mapped and dated to understand the impact of beavers on the geomorphology of rivers and wetlands.
Dated subfossil remains give direct evidence of beaver in the park since at least the middle Holocene, and a hughe population rise in the years before park establishment in 1872 and a decline until 1920 (maybe because of competition with elks).

Diagnostic characteristics for deposits of beaver ponds mapped were determined by detailed field analysis of texture, sedimentary structures, Munsell soil color chart, and organic content, emphasizing features that distinguish beaver-pond deposits from other fluvial sediments. The sediments are characteristic fine-grained, deeperwater pond sediments, ranging from clay loam to loam, with minor sandy units. Pebbles and cobbles are sometimes scattered within deposits. Organic content in pond deposits is typically high, because of the habits of the beaver to introduce abundant organic debris in the pond, also some larger wood pieces showed beaver-gnawed ends. Beaver pond deposits were identified on parts of all streams examined, and individual pond deposits, i.e., those with no break in vertical sequence, ranged from 0.2 to 1.2 m thickness.

Incised-channel exposure on middle Elk Creek (Yellowstone National Park) showing 14C-dated beaver-pond deposits separated by oxidized gravel (~1.1–1.5 m depth).
Note stratigraphic position and age of ~1120 cal yr BP age from a beaver-gnawed Douglas-fir (Pseudotsuga) stump in growth position. The beaver-pond sediment shows lamination and contain organic-rich layers, pebbles, coarse to fine sand, and silt (from PERSICO, L. & MEYER, G. -2009, copyrigth 2008 University of Washington).

The chronological data, ranging between 7000 and 50 years seems to show a weak correlation of beaver dam sediments with cooler, and effectively wetter, climate phases, like the little Ice Age (~650–100 cal yr).The concentration of dated pond deposits in the last 4000 yr, essentially Neoglacial time, may also partly reflect a generally cooler climate and more reliable streamflows.
Historical climate records in the Yellowstone area show a trend toward a warmer and generally drier climate from 1895–1990 that has continued to the present, so some authors inferred that drought and reduced streamflows, especially in the 1930s, were partly responsible for the marked post-1920s decline in the beaver populations.

The amount of stream aggradation that can be attributed to beaver ponds is small, 2m for a single beaver pond, up to 2,5m for depositions with intervals between (with ages of deposition ranging between ~7000, 2600, 900, 400, and 50 yr mean ages).
Also, glacial erratic boulders along several rivers have not been buried by beaver-pond or fluvial deposits, indicating little net postglacial aggradation.

This results relative the importance of beavers as geomorphologic factor, that contribute only small amounts of sediment aggradation in river systems, nevertheless they play a role in a local context. The presence and the extent of the population of beavers is also influenced by ecological factors, like food ressources and competition, that themselves depend of the overall climate.

PERSICO, L. & MEYER, G. (2009): Holocene beaver damming, fluvial geomorphology, and climate in Yellowstone National Park, Wyoming. Quaternary Research. IN PRESS

Freitag, 27. März 2009

Science Spiderweb

How are scientific disciplines (inter)connected, and how can we visualize the resulting web? Now a reserach team has developed such a map - showing the interactions between various fields ranging from human to natural sciences by using the search path and traces of more then 1 billion users in the Internet.

A galaxy of science with various clusters...and guess where "geology" can be found?

Freitag, 20. März 2009

Rockslide Days !

01. - 04. 10. 2009

Rockslide Days!

Institute of Geology, University of Innsbruck

Three-day expert field workshop in selected rockslide deposits of the Alps

The aim of the workshop is to bring together experts in the phenomena of mass-wasting for discussions of problems and strategies, right at the outcrops.

Donnerstag, 19. März 2009

Re: Fluvioglacial sediments from Baumkirchen (Austria)

Johannes has a very interesting post about his memorys on a visit to the (or at least one of the) key sites for the quaternary history of the eastern Alps - Baumkirchen, and his fluvioglacial clays (even if they in reality are fine sands, with "true" clay-minerals missing).
C14 dates have given an age of 31.000 to 27.000 years, a dated wood of
Pinus sylvestris - but found in a slumped area- gave a date of 11.000 years B.P (FLIRI 1973).
There were even some fossils, mostly pollen grains and parts of arthropods (ostracods and insects), but also some mysterious ichno-fossils:

FLIRI (1973): Beiträge zur Geschichte der alpinen Würmvereisung: Forschungen an den Bändertonen von Baumkirchen (Inntal, Nordtirol). N.F. Z. Geomorph. Bd. 16: 1-14
RESCH (1972): Mikropaläontologische Untersuchungen im Bänderton von Baumkirchen (Inntal, Tirol). Zeitschrift für Gletscherkunde und Glazialgeologie. Bd. 8: 215-230

Mittwoch, 18. März 2009

Mysterious boulder ?

The term „Geschiebe“ in german is unfortunately ambiguous, or at least used so. It can indicate sediment transported by a river, or by a glacier too. Geologists use the name traditionally for glacially transported sediments, limnologist and water engineers use it in the second meaning of the word, confusion – even indicating if the term is used in the glacial or fluvial sense, is secured.
But what´s now the mysterious boulder? It was found in an outcrop that at first looks seems a diamict with no apparent internal structure, single larger polimict clasts in a loamy to sandy matrix. A morain?

But a more precise observations of the larger clasts shows a distribution in single clusters, and an suggested imbrication (note granite-clasts, ca. in the middle and extreme right of the picture).

Also the landscape is very flat, or has only a gentle dip, not so typical for morain deposits, but commonly found in fluvial or limnic deposits deposited in large braided river systems.

So I tend to attribute this deposits to a fluvial system of high energy, with sporadic floods capable to transport even large boulders. The granite was first transported surely by glaciers (the actual catchment area don´t possess outcrops of this kind of lithology), but the final deposition occured by a river.
The disaggradation of the rocks must be happened after this second deposition – the boulder couldn´t possibly survive a transport in this conditions. The lack of color alteration of the feldspat, and the „freshness“ of the mica, let´s assume mechanical weathering, maybe in a colder climate with strong thaw and freeze cycles.

So a proglacial sediment of a glacier feed braided river system still seems possible to explain this sediment..

Dienstag, 17. März 2009

Breaking Boulders with Bare hands

Granite is sure one of the toughest rocks on earth, but sometimes even this rocks get literally chrushed in a million pieces. The picture shows the same boulder before and after I gently touched it. Have I underevaluated my strength ?
Even the name given with the german term „Geschiebeleiche – bedload carcass“ decribes perfect the status in with this rock can be found.

Sonntag, 15. März 2009

Mummy Zoo

One classic movie-monster is without doubt the „mummy“, mostly of egyptian provenience and also of human shape (despite the fact that thousend of egyptian animal mummies are known). This intact corpses and the effort behind their conservation is fascinating even for us today. But there are not only artificial mummies, nature knows a lot of ways to „make mummies“. Corpses can be conservated in bog deposits- to acid for decomposing organism, or tar pits – to poorly oxiginated, or permafrost- to cold for an effective decomposition of organic matter.

Replication of the "Starunia Woolly rhinoceros" - mummy.

Mummies of extinct mammals of the ice age provide a variety of reserach – taxonomic relations and dispersal history can be studied trough the ancient DNA, the structure of soft tissue can be observed in detail, paleodiet can be inferred by the gut contents and feces, some animals shows pathological deformations or tissue changes and/or parasites, on some carcasses even the circumstances of the death can be observed and finally the surrounding findings can give clues for reconstructing the paleohabitat and the climate.

At least 16 species of ice age mammals have been found mummified complete or partially: woolly mammoth, Shasta, Jefferson´s and Patagonian ground sloth, woolly rhinoceros, Yukon horse, steppe bison, helmeted muskox, Harrington´s mountain goat, caribou, giant moose, black-footed ferret, collared pika, snowshoe hare, arctic ground squirrel and vole. From this species the best preserved and known examples are the 40.000 year old mammoth calf „Dima“, the 10.000 years old Shasta ground sloth from New Mexico, the 36.000 year old „Blue Babe“ bison, a 40.000 year old subadult helmeted muskox, a woolly rhinoceros from the Ukraine and a 40.000 year old black-footed ferret from the Yukon territory.
Most of this cited animals are preserved by freeze-drying in permafrost of Siberia, Alaska and Kanada. The ground sloths and mountain goats despite are preserved in cave deposits – perhaps the dry conditions of their habitats were mainly responsible for the good preservation. The mummies of Starunia, in the Ukraine (woolly rhinoceros and mammoth) are an exception, here the bodys were „pickled“ in salty groundwater and coated by natural occurring mineral waxes. It´s clear that the preservation and the taphonomy of this different faunal assemblages show some affinities, but also great differences.

The mummies of siberian woolly mammoths were the first discoveries of this kind, with the famous expedition that recovered the Berezovka mammoth in 1901, but local legends of „elephant like moles“ found in the high arctic are much older. The Berezovka mammoth was preserved very well, unfortunately between the discovery (1900) and the recovery (1901) some parts were scavenged and some bones broken.

The expedition was lead by Dr. Otto Herz and Eugen Pfizenmayer – zoologist of the Russian Academy of Science. The 29.000-33.000 years old mammoth – described by the two researches „stinking like a horse barn, mixed with the smell of a rotting carcass“ was a 35-40 old male, „sitting“ on the ground. Herz and Pfizenmayer deduced from different broken bones (rips, bladebone and pelvis) that the animal broke trough thin ice and was entrapped in a fissure. Then a mudslide engulfed the poor animal, causing death by suffocation, showed by the presence of plants still in the mouth and the erigated penis. Today the broken bones are interpreted to be a postmortem taphonomic event, caused by a landslide or crep of the material around the body.

The preserved penis of the mammoth.

To be continued...

Donnerstag, 12. März 2009

The Quaternary is dead, long live the Quaternary

The status of the Quaternary is still uncertain, and debated between the different geological associations.

Current status and some possible options for formalizing the “Quaternary” interval of Earth history. Durations of stages, epochs and “Quaternary” on the geologic time scale are according to their span in millions of years. The Neogene Period begins at ~23 Ma (after OGG 2004).

The INQUA (International Union for Quaternary Research), representing more than 50.000 Quaternary scientist, now has reconfirmed the proposal of 2005 in an open letter by the chairmen’s Prof. J.J. Clague and Prof. Brad Pillans (28.02.2009). During the “International Commission on Stratigraphy” Workshop (Leuven, Belgium, 1–5 September 2005) 12 votes of the members of the executive officers of ICS (International Comission on Stratigraphy) were favourable to maintain the Quaternary as Sub-Era, but to shift the beginning (option B).

IUGS (International Union of Geological Sciences) ratified the Quaternary as a Period/System on May 28, 2007 –legitimizing the recent and future use of this term - so now the actual discussion has to set the exact position of the base of the Quaternary and the base of the Pleistocene Epoch/Series and Gelasian Age/Stage. The INQUA supports the proposal to lower the base of the Quaternary from its present IUGS-sanctioned position at the base of the Pleistocene Vrica GSSP (1,8Ma) to the base of the Gelasian Stage GSSP (at 2.588Ma). The current boundery is inappropriate because there are no important global changes at 1,8Ma, without events that can be recognized and correlated globally.

To be continued...

Pliocene-Pleistocene section of marls at Lido Rossello (Sicily). The GSSP for the Gelasian is definied in the same formation (Trubi-Formation and Monte Narbone-Formation).

OGG, J. (2004): Introduction to concepts and proposed standardization of the term “Quaternary”. Episodes, Vol. 27, no. 2

Sonntag, 1. März 2009

Hydrogeology and Bugs

An actual issue of the “Hydrogeology Journal” is dedicated to an interesting approach for hydrogeological research and exploration – the possibility and the use of animal and plants for evaluating and prospecting springs and aquifers. Here I present a summary of this interdisciplinary research, with some personal experiences and considerations.

Maybe one simple definition of a spring is that it is a point(s) in which the groundwater table intersects with the Earth’s surface, so that the water spills over and become an open water body. Groundwater represents an important source of potable water – and so to understand the hydrogeology of springs is an important challenge for geologist.
Research on and the classification of spring in hydrogeology is traditionally done by physical parameters, like temperature, electric conductivity and discharge. These are important parameters that can provide clues of the catchment’s area, conductivity of the underground and connections to the surface, and capacity of the aquifer. But geologist are still searching for even more clues to understand the hidden paths of water in the underground, and use geophysical methods, geochemistry, prospecting by drilling, prospecting by satellites and maybe in future bugs…

A droplet of drinkwater from London (UK) as habitat, in a satirical caricature of the journal “Punch” from 1850. London got his first canalisation system in the first half of the 19th century – consisting simple of a collecting system discharging in the rivers of the city, where then again the drinkwater was won. The hygienic conditions were disastrous, causing epidemics spread trough the consumption of infected water, like typhus and cholera.

Springs are not only source for drink water for our daily use – but in first place they are places that can provide sustain and microhabitats for a large array of aquatic, wetland and terrestrials plant and animal species. This can be common species, not strictly bound to a spring habitat, but also species, bound strictly to the ecological conditions that provide springs – but because the habitat “spring” is often changed by human activity, in form of depleting the aquifer that feeds the spring, or using the spring itself for his uses, most of this life forms are seriously endangered.

Springs as habitats are still underevaluated and poorly understand – they represent ecotones – a connecting habitat between two different ecosystems, the groundwater and the surface(-water). Hydrogeologists have traditionally dealt with the point of emergence, paying little attention to springs after the point of discharge, where they are more interesting to biologists. Classification systems of surface waters or groundwater ecosystems have more incidentally included springs – in fact, there exist a lots of classifications systems, but no integrated system considering the mayor physical, biological and socio-cultural variables of springs.
The consideration of these variables can help to understand the hydrology of an aquifer, and unify the language between hydrogeologist and biologists, so that they can exchange information’s and ideas.

Step 1. – Unifying theory

The presence of a spring is constricted by some parameters. The proposed classification of SPRINGER 2008 include 12 spheres of discharge, controlled by geomorphic considerations (hydrostratigraphic units, emergence environment, orifice geomorphology, sphere of discharge, channel dynamics), forces bringing water to the surface (confined aquifer and artesian springs), flow properties (persistence, consistency, rate, variability), water quality (temperature and geochemistry), habitats (climate, surrounding ecosystems, habitat size and microhabitat variability), springs biota (species composition and diversity, vegetation) and spring management and use.

- Cave: Emergence in a cave (for example carst)
- Exposure springs: Cave, rock shelter fractures or sinkholes where uncounfined aquifer is exposed near the land surface
- Fountain: Artesian fountain or gas propelling the water column
- Geyser: Explosive flow of hot water from confined aquifer
- Gushet: Discrete source flow gushes from a cliff wall of a perched, unconfined aquifer
- Hanging garden: dripping flow emerges usually horizontally along a geologic contact along a cliff wall
- Helocrene: Emerges from low gradient wetlands; often indistinct or multiple sources seeping from shallow, unconfined aquifers
- Hillslope: Emerging of a un-/confined aquifers by indistinct or multiple sources seeping out on a hillslope
- Hypocrene: A buried spring where flow does not reach the surface, typically due the very low discharge and high evaporation or transpiration (“wetland”)
- Limnocrene: Emergence of un-/confined aquifers in pool(s)
- (Carbonate) mound-form Rheocrene: Flowing spring, emerges into one or more stream channels


SPRINGER, A.E. & STEVENS, L.E. (2009): Spheres of discharge of springs. Hydrogeology Journal 17: 83-93