Historic earthquakes in Japan

Japan is situated in the collision area of four great lithospheric plates: the Eurasian/Chinese Plate, the North American Plate, the Philippine Plate and the Pacific Plate. The continuous movements of these plates generate a lot of energy released from time to time in earthquakes of varying magnitude and effects and so unfortunately catastrophic earthquakes are nothing new for this region.

Destructive earthquakes occured in Japan for several times in the last centuries. From 1930 until today 10 stronger earthquakes have killed more than 18.000 people and destroyed hundreds of thousands of buildings. Many earthquake were associated also with devastating tsunamis.

Written Japanese records of strong earthquakes and their aftermath date back at least 1.600 years. Until 1860 however Japanese naturalists were less interested in exploring the cause of earthquakes than their effects, and mythical explanations and divine intervention prevailed.

Fig.1. This wood print of the year 1855 shows the god Kashima overlooking the sentence of the giant catfish Namazu, accused to have caused the devastating Edo-earthquake in 1855. A helper of the god - a daimyojin - uses a big hammer to beat the magic capstone into the head of the catfish and immobilize him. The scene is observed by an assembly of small catfishes, representing earthquakes of the past (from BOLT 1995).

In the year 1600 the Japanese nobleman Tokugawa Ieyasu chose the village of Edo (modern Tokyo) as his new residence, three years later it was the capital of the unified Japan. The city rapidly grew and soon reached hundreds of thousands of inhabitants - one of the largest cities at the time. Unfortunately this strategic position at the bay of Tokyo was and is also a highly seismic area.

Fig.2. Copper engraving published in 1669 by an anonymous European artist possibly illustrating an earthquake in Edo (modern Tokyo) in the year 1650. It is not clear if the artist experienced the earthquake himself or based this figure on eyewitnesses' accounts of unspecified earthquakes, nevertheless it presents one of the oldest known illustrations of a Japanese earthquake (after KOZAK & CERMAK 2010).

December 31, 1703 Japan was hit by a strong earthquake (with an estimated intensity of 8 after the Mercalli-scale), in Edo most of the buildings constructed of wood collapsed. More than 6.500 people were killed by a flood wave, which caused havoc in the bay of Sagami and on the peninsula of Boso. This earthquake and its aftermath effects, like flood and fire, killed estimated 150.000 people.

One of the most remembered earthquakes hit Tokyo on November 11, 1855 (the Ansei-Edo earthquake). It was one of the most destructive quakes (with a magnitude of 7.3), killing estimated 16.000 - 20.000 people. From this event many woodblock art prints still exist, displaying the destruction and telling of the despair of the survivors.
Fig.3. and 4. Anonymous contemporary woodcuts of Edo before and after the great 11 November 1855 magnitude 7.3 Ansei-Edo earthquake, from KITAHARA et al. 2003.
 
October 28, 1891, the agricultural Nobi region, north of the city of Nagoya, experienced an earthquake of magnitude 8. Modern buildings made of bricks as wooden traditional houses were heavily damaged or collapsed, hundreds of thousands became homeless and 7.000 people were killed.
The English geologists John Milne (1849-1913), who in 1880 founded the Seismologists Society of Japan, studied the effects of the earthquake and published an important monographic work "The great earthquake in Japan, 1891". The Japanese geologist Bunjiro Koto observed a superficial dislocation of the landscape by 4 meter as the origin of the earthquake and recognized a fundamental principle in seismology: that faults are not the result of an earthquake, but its cause.

During the second half of the 19th and early 20th century scientific research on earthquakes became rapidly established in Japan.
 
Fusakichi Omori (1868-1923), director of the Seismological Institute of Japan, studied the occurrence of earthquakes around Tokyo and wrote in 1922:

"Currently the immediate area of Tokyo is seismically quiet while in the mountains around Tokyo in a distance of about 60 kilometres there are often triggered earthquakes, which - although they are may felt in the capital - are in fact harmless, because the affected areas are not part of a larger destructive seismic zone.
Over time, the seismic activity in these areas will gradually diminish, meanwhile it will increase as compensation in the bay of Tokyo and will possibly cause a strong earthquake. An earthquake with an epicentre at some distance from Tokyo would be have a half-destructive, local impact."

One year later, September 1, 1923, the city of Yokohama and Tokyo were hit again by an earthquake, today remembered as the Great Kanto- earthquake with a magnitude of 7.9 on the Richter-scale and the epicentre situated in the bay of Sagami.
More than 99.000 people were killed by the collapse of buildings, a 10 to 12 meter high tsunami and a fire that raged for 2 days in the city. The bodies of possibly more than 40.000 people were never found. The first day of September is today a national day of remembrance for the dangers of earthquakes.

June 28, 1948 the American photographer Carl Mydans visited the city of Fukui to document the post-war development of this important industrial city. At 17.14 Mydans was surprised by a strong earthquake in the American military base, he remembers:

"The cement of the floor crashed. Dishes and tables were spun into our faces and we all found us in a mad dance…[]… when I found myself near the entrance, I moved into it's direction. But the floor slipped away under my feet and I rushed against a crumbling wall."

Mydans turned back to get his camera and in the next 15 hours documented the desperation and destruction of the 7.3 magnitude that destroyed Fukui and killed 5.131 people.

Fig.5. A woman tries to escape, avoiding large fissures opening in the ground. The photographs by Carl Mydans are unique documents of the terrible aftermath of the Fukui-earthquake of 28. June 1948.

According to Mydans, most of the victims perished entrapped under the debris or in the fire after the earthquake. Shocked by the lack of tools to remove the debris, Mydans promoted the distribution of emergency-boxes, equipped with an axe and other heavy tools.

In January 1995 the industrial city of Kobe was heavily damaged by an earthquake with a magnitude of 7.2 after Richter, the strongest earthquake in Japan since 1923. More than 6.000 people were killed and more than 300.000 people lost their homes.

The recent tragic earthquake of March 2011 with a magnitude of 8.9 (possibly 9.1, there is also a map showing the intensity after Mercalli) is covered by various geobloggers.

Fig.6. Map of Japan showing a selection of earthquakes with a magnitude greater than 7 after Richter in the last 100 years and major historic events (data from U.S.G.S. 2005, file download from Exploring Africa's Physical and Cultural Geography using GIS), see also Seismicity of the Earth 1900—2007, Japan and Vicinity.

Bibliography:

BOLT, B.A. (1995): Erdbeben - Schlüssel zur Geodynamik. Spektrum Akademischer Verlag, Berlin: 219
GUNN, A.M. (2008): Encyclopedia of Disasters - Environmental Catastrophes and Human Tragedies. Vol.1. Greenwood Press, London: 733
KITAHARAK, I. et al. (2003): Documenting Disaster, Natural Disasters in Japanese History, 1703-2003. Nat. Museum of Japanese History, Chiba.
KOZAK, J. & CERMAK, V. (2010): The Illustrated History of Natural Disasters. Springer-Verlag: 203

Mediterranean desiccation and giant evaporates

Outcrops of salt-bearing and gypsum-bearing sediments in the Mediterranean region were already noted by geologists in the late 19th century. In 1849 the Italian chemist J. Usiglio conducted evaporation experiments with seawater along the French Riviera and established the order in which evaporate minerals precipitate. It seemed clear that the salt deposits cold be explained by changes in the distribution of sea and land, but the extent and thickness was impressive.
Karl Mayer-Eymar (1826-1907) a Swiss geologist and palaeontologist, dated the sediments by fossils in the Miocene Epoch and in 1867 named the period the Messinian, for the Italian region of Messina. The formation of these deposits however remained a riddle.

In 1961, seismic surveying of the Mediterranean basin revealed a geological feature some 100-200 metres below the seafloor. This feature, dubbed the M-reflector by its strong property to reflect the seismic signals, closely followed the contours of the present seafloor, suggesting that this presumably compact layer was laid down evenly and consistently at some point in the past. New and high quality seismic data on the M-reflector were acquired in the Mediterranean Basin in 1970, at the same time the M-layer was cored during the Leg 13 (Site 124) of the Deep Sea Drilling Program conducted from the Glomar Challenger under the supervision of co-chief scientists William B.F. Ryan (specialized in geophysics) and Kenneth J. Hsü (specialized in sedimentology). One of the goals of the two young scientists (criticised by some older colleagues as "student and amateur") was to reach the mysterious M-layer.
Only the second attempt in the Balearic Basin off the Spanish coast was (sort of) successful, the drill string begun to vibrate and finally got jammed. Recuperated the drill bit only some loose debris could be collected from the deep underground. Ryan and Hsü along with palaeontologist Maria Bianca Cita begun to study the apparently disappointing sample, but soon they discovered some strange properties.
The debris consisted of basaltic rocks, white limestone, transparent crystals of gypsum and microfossils. Especially the microfossils were interesting; shoal-water foraminifers, but also tiny mollusc shells. According to Cita the organisms were small and underdeveloped, maybe as response to an extreme environmental stress.
Ryan and Hsü soon recognized that the basalt clasts were cobbles and pebbles formed by fluviatile transport, the limestone and gypsum the remains of a sabkha and the micofossils inhabitants of a hypersaline lake.

To form such a succession of lithological facies in situ only one explanation was possible: the entire Mediterranean Sea disappeared some 7 million years ago. This desiccation hypothesis caused mixed reactions by the scientific community, and is still under scrutiny today, especially because this relatively recent event could maybe represent a model to explain large evaporate deposits in the geological past.

Even today the Mediterranean Sea is characterized by a semiarid climate with low precipitation and high evaporation. The amount of fresh water flowing into the sea by rivers is not sufficient to compensate the loss; however the inflow of 2.000 square kilometres per year from the Atlantic Ocean trough the strait of Gibraltar holds the Mediterranean Sea level constant. If this connection would be sealed, in only some thousand of years the Mediterranean Sea would almost evaporate completely.
During the late Miocene - the Messinian Stage (7,2-5,3Ma) - tectonic forces between the European and African plate pushed up the Spanish Sierra Nevada and closed the strait of Gibraltar. By the evaporation of the seawater various evaporitic minerals became deposited like halite, anhydrite, gypsum and others, forming finally a succession of sediments incredible 2.500 meters thick.
Most of these evaporates still lie hidden underground or under the bottom of the sea, however in Italy these sediments became uplifted by tectonic forces during the orogenesis of the Apennines. On the southern coast of Sicily, near the village of Eraclea Minoa, in the Messinian sediments at least six cycles can be observed, from beds of gypsum crystals to fine laminated marls and claystones to crystalline layers of selenite, capped again by sandstone.

Fig.1.

Fig.2.Fig.3.

Fig.1-3. Outcrop of Messinian evaporitic sediments at the Eraclea Minoa site in Sicily. The resistant gypsum beds are less eroded by weathering processes than under- and overlying marls. The upper crystalline selenite domes (in Italian called Gessoso-Solfifera, fig.2.) of cycle 4 were formed in shallow lagoon conditions and are cropped by fine laminated marls and gypsum beds (Balatino, fig.3.) at the base of cycle 5. In the background of the photo cycle 6, characterized by much thicker marls and claystone deposits than the previous cycles, is recognizable, covered by the Pliocene.

The base of the Pliocene (GSSP Messinian-Zanclean 5,332Ma) is formed by the sandstone of the Arenazzolo-Formation, followed by grey marls of the Trubi-Formation.

The base of the succession is formed by reworked debris of basaltic rocks, followed by conglomerates, sandstone, laminated marls and evapoitic layers. In the sediments various cycles of marls and gypsum beds are recognizable, it is not completely clear if this succession is the result of repeated flooding and desiccation of the entire Mediterranean Sea (if so, at least 24 such cycles are recognized) or local events in tectonic active basins.
Fig.4. Example of the Messinian succession of facies from the section North-West of Alba (Tertiary Piedmontese Basin) as drawn by the Italian geologist Sturani in a Seminar in October 1975 (LOZAR et al. 2008). The section starts with silty clays and marls of a normal marine environment, truncated by sand, silts and clays followed by silty clays with stromatolithic limestones. Here we observe a decrease of depth from a intermediate depth facies to a shallow lagoon with first evaporitic phases. In a restricted lagoon clays with lenses of early diagenetic selenite form, changes in water circulation occur as indicated by the fossils and a succession of silts, silty marls and sand beds. Then in an alluvial plain or marsh evenly bedded, massive clays were deposited. The entire section is cropped again by normal marine, Pliocene clays and marls.
 
More than 5 million years ago the sea finally returned to stay. The entire evaporate succession is cropped by marine sediments, first the Arenazzolo-Sandstone of the brackish Lago-Mare-Unit and then deep sea turbiditic marls of the Trubi-Formation.

The following video from the TV-documentation "Europe: A Natural History/Wild Europe" (2005) oversimplifies the story and presents uncritically some inaccuracies, like the reconstruction of a surprisingly narrow dam at Gibraltar and the infill of the Mediterranean Sea directly by the modern strait (there was probably an episodic connection to the Atlantic more to the north), but it gives a graphic and overall idea of the event.

Bibliography:

FISCHER, A.G. & GARRISON, R.E. (2009): The role of the Mediterranean region in the development of sedimentary geology: a historical overview. Sedimentology 56: 3-41
LOZAR, F.; MARTINETTO, E; DELA PIERRE, F., TRENKWALDER, S. & VIOLANTI, D. (ed.) (2008): Messinian Palaeontology - Papers in honour of Carlo Sturani´s outstanding contributions in geology and palaeontology. Bollettino della Societá Paleontologica Italiana Vol. 47(2): 202MORRISON, P. & MORRISON, P. (1988): Das Geheimnis unserer Wahrnehmung - Warum wir wissen, was wir wissen. Droemer Knaur Verlag, München: 320
USIGLIO, J. (1849): Analyse de l´eau de la Mediterranée sur le Cotes de France. Ann. Des Chem.Phys., Third Ser. 27 :92-107

A geologist riddle #7

An "impossible" outcrop - the rocks where already recognized in 1867, but only a discovery in 1970 revealed an incredible environmental change - what is the significance of this site?

Accretionary Wedge #32: A favourite image

The Accretionary Wedge of March is asking for your "favourite geologic picture" and is hosted by Ann's Musings.

In a first moment I couldn't decide what image to take, the classic outcrop or the marvellous landscape? - but there is an elder picture of 2007 I really like, at a first glimpse it's geological context is not obvious, but this is also a reason that I like this particular picture.

The photo shows a species of club moss emerging from a pile of rubble. The club moss Huperzia selago is one of the two species of this genus present in the Alps; this species in particular can be found in high altitude and in glacier forelands, acting as pioneer species.
This specimen was emerging from gneiss and schist debris covering an active rock glacier; I like the contrast of the green plant to the cold grey of the rocks forming a sort of picture frame, the impression that the club moss overcomes every obstacle, even "breaks" the rocks apart to emerge from the underground.
For plants creeping debris and permafrost represent an ulterior challenge for colonization and growth in an already nasty environment, with long snow cover, low temperatures and deadly UV-radiation. I think the picture depicts well the struggle of existence in a harsh environment - but as the the rocks act as obstacle they at the same time also provide shelter, moisture and nutrients.

For the geologist also the recognition of even the smallest clue can be helpful, I find it fascinating how many different methods can be adopted to understand the development of a geomorphologic feature or a landscape - in combination with classic geological methods for example the vegetation cover or diversity can give indications of the recent activity of rock glaciers, or help to reconstruct the temporal development when other indicators are absent.

And finally the image remembers me as a sort of metaphor what the German geoscientist Gerd Lüttig argued in 1971:

"Earth history can be described as a permanent interaction between the geosphere (lithos) and life processes (bios). To investigate these processes is the mission of Lithobiontics, a new research discipline between Geology and Biology."

Tasman Glacier

The magnitude 6.3 earthquake that hit the last February 22 New Zealand not only caused havoc in city of Christchurch but also affected the Tasman Glacier, nearly 200 kilometres to the west of Christchurch.
Ice with the overall mass of 30 million tons broke off from the glacier tongue, a fragment nearly 1.200 meters long and 75 meters broad. Eyewitnesses report that the break-off caused a three meter high wave.
The glacier tongue was already instable and closed for tourists due to heavy rain in the last months. The water from above, in combination with the water of the lake, melted large quantities of ice and destabilized the glacier.
Like many glaciers worldwide also the Tasman Glacier is retreating since 1976, in the free space between the actual glacier and the moraines a ice-contact lake developed. The contact between ice and water accelerates melting and iceberg calving from the glacier.

Fig.1. Tasman Glacier with the Tasman Lake, the icebergs at the southern border of the lake are the remains of the collapse caused by the earthquake February 22 (ASTER-image by NASA, 02 March 2011). The comparison with older images show that mostly a part on the western lakeshore disappeared.

The Anthropocene and the sixth Extinction

"I see the destructive side of humankind, the blind spider; she fiddles in the poisonous gloominess, dreaming dreams full of mushroom clouds. All is explained by death, she whispers."

"The Martian chronicles", Ray Bradbury (1950)

In 2002 the chemist Paul Crutzen suggested that the effects of human population and culture on the environments of earth are so pronounced, that they will leave a permanent geological marker in the stratigraphic record of the planet. Most geological epochs were defined in historic times by observed geological changes in lithology, petrology and especially paleontological content -the extinction and replacement of species in the fossil record.

Fig.1. The "Appearance of Man", by L. FIGUIER 1872.

Humans artefacts where recorded in the stratigraphic column since our first ancestors developed lithic industry, but only in the Holocene human activity and influence on environment is observable in the deposited sediments.
The use of fire to clear land and hunt animals maybe has forced the extinction of the Pleistocene Megafauna. With the development of agriculture and pasture the pollen spectrum of plants recorded in bog sediments shifts significantly, tree species diminish, grass and cultivated plants increase.
With the first civilisations, geochemical changes as results of environmental pollution by mining and handling of metals are observed in lake sediments and in the ice records of Greenland.
The impacts of humans increase during the second half of the Holocene as a result of increasing population and development of large civilisations, with many humans working together to realize projects that single individuals couldn't possible achieve by itself.

In the last 200 years humankind has surpassed all efforts of previous generations. Humans use the majority of natural resources, like soil and water. Water is stored of redirected, and soil and sediments are cultivated, excavated, transported and deposited, influencing sedimentation patterns and causing a lithological change in the geological record.
The burning of fossil fuels has altered the chemistry of the atmosphere, that on its own will influence temperature and precipitation, again influencing erosion (for example improved chemical weathering) and deposition.
The arguments were considered by some geologists and a term coined for a possible new geological period - the Anthropocene, used informally in literature to refer to the actual period since the Industrial Revolution, when our technology enabled us to previous unthinkable efforts to shape earth and nature.

The mentioned Pleistocene extinction proceeds with increasing speed on land and in the seas, active hunt, destruction of habitats, relocation of animals and plant species, spread of pathogens, climate change have all catastrophic effects of the native fauna and flora.
The results are permanent in the fossil record, extinct species are no longer available to evolve, and future evolution will take place on surviving (and frequently anthropogenic relocated) stocks.

Is the modern loss of species already comparable to the geological past?

99% of all species ever lived on this planet in the last three and a half billion years went extinct - extinction is the rule, not the exception, however the constant rate of extinction and speciation was interrupted by phases of increased velocity in the loss of species.
In all cases the exact mechanism is still poorly understand, possible factors contributing to the disappearance of species are geological catastrophes like volcanism, impacts or climate change, but also biological factors like competition, diseases or depletion of resources. Mass extinctions are characterized by the increase in both extinction rate (loss of species per time) and extinction magnitude (amount of lost species) compared to the normal geological background. It is notable that during mass extinction all kind of organisms group, if worldwide distributed or local, if generalists or specialized, if numerous or rare, if large or small can be affected.
In the record of earth five large, natural occurring mass extinctions (the big five), characterized by the loss of at least three-quarters of species in a geologically short interval (typically less than 2 million years), are recognized: near the end of the Ordovician, Devonian, Permian, Triassic and of the Cretaceous Periods.

To compare these past mass extinctions to the assumed modern one is complicated by the incomplete record of both fossil as living species. Fossilization is a rare event, many organisms without hard parts like bones or shells are presumably lost forever and many fossils maybe still slumber undetected in remote parts of the globe. If a species is described based on the recovered remains this concept of species can be in conflict with the modern definition of species, many species described on fragments were subsequently discovered to belong to a single species.
Also our knowledge of the modern biodiversity is far to be complete, especially small critters, like bugs or other invertebrates, are much underrepresented when compared to mammals or other vertebrates in the studied and described species. In addition from most of the described species the conservation status is unknown.

Considering these problems, a published study by BARNOSKY et al. 2011 tried to compare the mass extinctions with the actual loss of species. Today from 48.000 species in the Red List compiled by the International Union for Conservation of Nature (IUCN) 3.325 are at risk of extinction and 17.300 threatened.
By considering the extinct species of birds, reptiles, amphibians and mammals in the last 500 year period, it was possible to determinate the actual extinction rate and to extrapolate it to match the past mass extinctions.
According to the calculation the extinction rate today is already significantly higher then the background rate and depending on the scenario (assuming that the today threatened species will be extinct in the next 100 years) an extinction rate comparable to the past mass extinction can be reached in the next centuries to millennia.

Despite these gloomy predictions there is still a glimpse of hope, in historic times we have actually lost only a few per cent of described species, still from a paleontological view the modern extinction rate is lower than the past big five, but there remains little time and much to do to avoid the human induced sixth mass extinction.

Bibliography:

BARNOSKY, D.A.; MATZKE, N.; TOMIYA, S.; WOGAN, G.O.U.; SWARTZ, B.; QUENTAL, T.B.; MARSHALL, C.; McGUIRE, J.L.; LINDSEY, E.L.; MAGUIRE, K.C.; MERSEY, B. & FERRER, E.A. (2011): Has the Earth's sixth mass extinction already arrived? Nature Vol. 471: 51-57
FIGUIER, L. (1872): The World before the deluge. Cassel, Petter, Galpin & Co.: 518
ZALASIEWICZ, J. & WILLIAMS, M. (2008): Are we now living in the Anthropocene? GSA Today Vol.18 (2): 4-8

The Iceman story

"I remembered the effect that the view of the tremendous and ever-moving glacier had produced upon my mind when I first saw it. It had then filled me with a sublime ecstasy that gave wings to the soul, and allowed it to soar from the obscure world to light and joy. The sight of the awful and majestic in nature had indeed always the effect of solemnising my mind, and causing me to forget the passing cares of life. I determined to go without a guide, for I was well acquainted with the path, and the presence of another would destroy the solitary grandeur of the scene."

Mary W. Shelley "Frankenstein" (1813)

It was a fast and lonesome death, wounded by an arrow in the back, the man bleed to death within minutes. The body was left on the site of the murder, maybe the aggressors assumed that scavengers and time would erase all of the evidences, but in the cold and dry climate the body begun to desiccate and large scavengers didn't venture in this desolate realm, only some flies were able to deposits their eggs on the body but they weren't able to destroy it.
During the next winter snow accumulated in the gully where the body laid and in the next decades and centuries the snow transformed slowly into ice, protecting and preserving the mortal remains.

Fig.1. The small snowfield on the middle of this photography is covering again the gully in which the body of "Ötzi" was discovered.

Time passed, then in the late summer of 1991 - exact 20 years ago- two German tourists, Helmut and Erika Simon, accidentally discovered the body emerging from the ice, the marked ablation during the summer (helped by sunny weather and the deposition of Saharan dust on the glacier ice, that absorbed much solar radiation) of the small glacier near the Similaun Hut, in the Ötztaler Tyrolean Alps, brought the corpse back to the surface.
The prehistoric mummified corpse - soon known worldwide as "Ötzi" the Iceman - together with its unique set of artefacts, provided a unique opportunity for the research of the cultural development of a bronze-age culture, this corpse is the highest prehistoric find (ca. 3.280m a.s.l.) in the Alps.

But the body and artefacts provided also insights on the glacier dimensions during the little known phases of the warmest parts of the Holocene in Europe. This phase is practically undocumented by glacial sediments, eroded by later glacial advances, and is only recognizable by proxy data like changes in pollen diagrams or dating organic materials, over- or underlying glacial or proglacial deposits.

During the last glacial maximum some 18.000 years ago the entire area was completely ice-covered, only narrow and steep arêtes and horns protruded from the ice. In the area of the Similaun Hut sharp trim lines in a height varying from 3.060m to 3.400m divide the uppermost frost-shattered crests from the lower slopes, smoothed by glacial erosion. The trim line can also recognized locally as marked weathering line that separates different oxidized surfaces (the bed rock consists of Fe-rich gneiss and schist).
A second trim line is marked by an abrupt change in lichen diameter (from 100mm above to 40mm below) and density. The dating by lichenometry attributes this glaciers to the Little Ice Age (LIA, ca. 1.600-1.850), which generally corresponds to the maximum Holocene glacier expansion.
The mummy itself was dated by radiocarbon dating to 4.500+-30 and 4.580+-30 yr B.P., which corresponds to a calibrated age of 5.300-5.050 yr B.P. The relatively sudden burial of the corpse in a more or less permanent snow and ice cover indicates a significant climatic change that induced glacier expansion at the beginning of the Neoglaciation in the second half of the Holocene.
This supposed change of the glaciers was supported also by some soil horizons found in depression between 3.000 and 3.215m a.s.l. and dated to 5.615+-55 yr B.P. (6.450-6.300 cal yr B.P.) and 3.885+-60 yr B.P. (4.416-4.158 cal yr B.P.). Similar recent soils needed at least 5 to 12 centuries for its development, suggesting that the climatic conditions on the site were for a long time relative favourable for biological and chemical activity.

The Iceman and his site so reveal that between 9.000 and 5.000 yr B.P. the mountain glaciers were smaller than in the second half of the Holocene. About 6.400 cal yr B.P. and for several centuries after, an ice-free peripheral belt allowed the accumulation of organic matter and developments of relatively thick soils. Between 5.300 to 5.050 cal yr B.P. ago a rapid climatic change took place, producing a persistent snow cover and the expansion of glaciers, which conserved the body until again the glaciers begun to retreat.
And the recent retreat of the glaciers still continues, in 1970 the glacier that revealed the mummy was part of the much greater Niederjoch Glacier, a composite alpine glacier that descends northward in the Nieder-Valley, but only in the last 5 years the Niederjoch-glacier lost 60-100m length.

Fig.2. The "Similaun" as highest peak (3.597m a.s.l.) with his two main glaciers, the "Similaun" in foreground, and the "Niederjoch" in background. Until ca. 1970 the glaciers flowed together, but the glacier retreat in the last years was notable.

Fig.3. Location (black circle) of the site of the bronze-age mummy in the Ötztaler Alps. Blue areas represents the glacier extends in 2003, the red line the glacier extends during the Little Ice Age (ca. 1600-1850), blue, green and yellow the main glacier-stages during the Pleistocene-Holocene transition.

The environment in which the Iceman lived was characterised by a rich biodiversity, he could use and in fact used an astonishing variety of plants found in his living space.
Both the axe shaft and the long bow were found in the vicinity of the corpse and were made of yew (Taxus baccata), a resistant and elastic wood typ. The quiver for the arrows was made of caprine skin and was stiffened with the elastic wood of the hazel tree (Corylus avellana). The 14 arrows were made of the hard wood of the wayfaring tree (Viburnum lantana). One is repaired, the front end being restored with dogwood (Cornus). The dagger handle is also made by hard wood from a piece of ash (Fraxinus excelsior). Its sheath was knotted from the bark of basswood (Tilia). He carried also two containers made of birch (Betula) bark, in one were found charcoal pieces wrapped in Norway maple (Acer platanoides) leaves.
Several wood species could be identified from the charcoal remains, probably spruce (Picea/Larix-type), pine (Pinus mugo-type), green alder (Alnus viridis), some Pomoideae which were probably Juneberry (cf. Amelanchier ovalis), dwarf willow (Salix reticulata-type) and elm (Ulmus).
A sort of backpack was constructed from a thick branch of hazel (Corylus avellana) bent into a U-shape, together with two coarsely-worked laths of larch (Larix decidua).

The majority of wood species found with the Iceman grow in the montane regions (valley bottoms to 1.800 m), although some subalpine (1.800-2.500 m) and alpine (above 2.500 m) conifer species are also represented. Their ecological requirements point to the transition zone between thermophilic mixed-oak forest communities (Quercetalia pubescenti-petreae) and the montane spruce forest (Piceetum montanum). Norwegian maple (A. platanoides), European yew (T. baccata), ash (Fraxinus sp.), lime (Tilia sp.) and elm (Ulmus sp.) allow to infer a humid habitat with a mineral rich, free-draining soil and a mild winter climate.
All that is similar to the present-day conditions in the woodlands found on the slopes and in gorges in the lower Schnalstal and Vinschgau in South Tyrol, where it is assumed he lived.

So the botanical evidence seems to confirm a climate comparable to modern conditions, and implies a glacial extent similar, if not slightly minor to the present. This has very important influence on the reconstruction of past, and modern climatic and glacial development, and at last the actual discussion about climatic change.

Bibliography:

BARONI, C. & OROMBELLI, G. (1996): Short paper - the alpine "Iceman" and Holocene Climatic Change. Quaternary Research 46: 78-83
MAGNY, M. & HAAS, J.N. (2004): Rapid Communication - A major widespread climatic change around 5300 cal. yr BP at the time of the Alpine Iceman. Journal of Quaternary Science 19(5): 423-430
OEGGL, K. (2009): The significance of the Tyrolean Iceman for the archaeobotany of Central Europe. Veget. Hist. Archaeobot. 18:1-11