Водно-ледниковые ресурсы бессточных районов Западной Монголии: современная оценка и тенденции изменения

Azerbaijan: Land of Fire and Flood Ancient Mariners and a Deluged Landscape

Два или три года назад я получил первое электронное письмо от американского естествоиспытателя Ронни Галлахера. Письмо и приложенные фотографии древних береговых линий. В течение многих лет Ронни посвятил себя изучению позднечетвертичных трансгрессий Каспийского моря. В последние годы мы много переписывались, и вот сейчас я републикую один из первых обобщающих итогов его исследований. Всё это очень интересно не только мне, но, думается, и многим другим посетителям сайта. Разумеется, что как и всякая научная проблема, предлагаемая в статье версия достойна обсуждения. Это можно делать здесь в комментариях, можно и на форуме. - Алексей Рудой

4 апреля 2013 г. Вот, нашёл я и статью Ронни в бумажном варианте. Можно ссылаться, она чуть отличает от представленной здесь.

Azerbaijan: Land of Fire and Flood Ancient Mariners and a Deluged Landscape

By Ronnie Gallagher

Background.

Azerbaijan has long been known as the Land of Fire, but few realize that it has actually been subjected to massive floods in the past so creating a geography that was very different from what we see today. With the Caspian Sea level at 28m below average sea level, (b.s.l.) it is almost impossible to imagine an upper elevation of around 225m above sea level (a.s.l.) and a massive inland sea. And yet this is what strandline evidence reveals. This great flood most likely happened some 18ka to 16ka BP at the end of the Ice Age during deglaciation and cannot be explained by glacial melt water alone.

Geologists are aware of raised terraces in excess of 100m, though these have been attributed to tectonic or mountain building uplift of the Caucasus. Personal investigation however suggests that this is incorrect, and that several flooding factors had to be involved in the creation of the drowned landscape features.

Understanding Azerbaijan’s flood events has been a fascinating and complex study and may even provide explanations for legendary prehistoric flood stories in the Ponto Caspian region. A huge inland sea and associated waterways may also provide clues to the solution of other enigmas such as the large language diversity across the Caucasus. There would also be many more implications as a large body of water would have greatly affected regional climates, regional biogeography and human demographics. It also suggests that intercontinental navigation from the Aral Sea to the Marmara Sea / (almost the Aegean Sea) was possible for millennia in the late Pleistocene. If so, flooding and the eventual disappearance of the waterways will have influenced ancient human life and helped shape prehistory. Intriguingly, the flooded landscape may even be recorded, both directly and indirectly in the rock art of Gobustan.

Interest in Caspian Sea levels began with a visit to Gobustan in April 2000 and viewing the fascinating Stone Age rock art which accurately details the life and times of these ancient inhabitants. Amongst the petroglyphs were a number of boats dating back some 8000 to 9000 years BP showing multiple oarsmen. These hinted at higher sea levels and the possibility of long distance navigation. Indeed, the boat petroglyphs attracted the attention of Thor Heyerdahl, who had a lifelong passion for exploring mankind’s ancient migrations. Unfortunately like other archaeologists and scientists he was at a loss to understand the importance of the vessels particularly as the Caspian Sea is understood to be last connected to the Black Sea some 11,000 years ago. With the Caspian Sea some 4.5 km distant from Gobustan rock art reserve and textbooks informing that over the past 10,000 years the Caspian did not reach any higher than minus 20 m b.s.l., something was not right: there had to be missing pieces to the puzzle. Indeed trying to work out must have happened is like finding bits of a jigsaw puzzle (evidence) and trying to assemble a picture with no clear idea of what the big picture might have looked like. The story is far from complete but an image has emerged that in my mind begins to challenge current understanding of events during and at the end of the Ice Ages.

For example, the presence of mysterious carved channels called ‘cart ruts’, near Baku which are very similar to those found in Malta and indeed throughout the Mediterranean region. Cart ruts are a feature of a Neolithic maritime culture. This raises the question of possible connections between the Mediterranean and the Caspian Sea. (Gallagher, 2002)

These enigmas called out for investigation and became an absorbing and wide ranging study. Looking into geomorphological, biological, archaeological aspects has revealed a story of epic proportions. In order to make sense of the terraces and strandlines it has been necessary to consider factors in additon to glacial meltwater, such as diverted Russian rivers, glacial dam collapses in the Altai region and even the influx of water from the Arctic Ocean. From geomorphological evidence (terraces and strandlines) it is clear that momentous events took place and need to be explained. This article aims to present a range of information that considers different events from current scientific understanding. The interpretations may turn out to be wrong, but the ideas are amenable to scientific and academic investigation.

Introduction

Fluctuations in the level of the Caspian Sea have greatly influenced coastal communities for millennia. This is due to the dynamic balance between regional climate, temperature, rainfall in the catchment areas of the rivers feeding the basin (principally the Volga), and evaporation from the surface of the sea. As an endorheic basin (i.e., having no outflow), water level will either rise or fall depending on climate and rainfall.

In the present era, fluctuations are only of the order of a few meters, and while significant to those living near the coastline, variations are minor when compared to the dramatic regressions and transgressions associated with the Ice Ages (Mamedov. 1997). A Caspian Sea high stand of 50 m above average sea level some 15,000 years ago is considered be the highest elevation over the past 100,000 years (Baker. 2007). Scientific understanding is that, during ice ages, the Caspian Sea greatly shrinks due to a cooler, drier climate. But at the end of an ice age, meltwater inundates the northern watershed areas and drains via river systems into low-lying basins of the Aral, Caspian, and Black Seas. Additional ice cap melting from the Caucasus, Himalayas and Hindu Kush supplements the inflow. Azerbaijan’s terraces, strandlines demonstrate that this is not a completely accurate picture as other factors seem to be involved.

Ice Dammed Lakes.

It is recognized that during Ice Ages Arctic Ocean ice fronts advanced onto mainland Russia and blocked the north-flowing rivers (Yenissei, Ob, Pechora, Dvina, and others) that supply most of the freshwater to the Arctic Ocean (Baker, 2007), (Grosswald, 1998), (Mangerud et al., 2001 and 2004), (Rudoy, 1998). As a result, large ice-dammed lakes formed between the ice sheet in the north and the continental water divides to the south. Lakes overflowed toward the south and, thus, the drainage of much of the Eurasian continent was reversed. The result was a major change in the water balance on the continent, decreased freshwater supply to the Arctic Ocean, and hugely increased fresh water flow to the Aral, Caspian, Black, and Baltic seas. (Figure 1). A consequence of this is that the world’s longest river was created from Siberia to the Mediterranean with the Aral and Caspian Seas becoming sediment traps for the diverted rivers.

Figure 1. Diagram showing the Eurasian ice sheets, pro-glacial lakes and diverted river route from Siberia to the Ponto Caspian region.

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25.03.2013 20:01 169 0 Комментарии

Ключевые слова:

• azerbaijan land of fire and flood ancient mariners and a deluged landscape caspian lake

В. Р. Алексеев. КРИОВУЛКАНИЗМ И ЗАГАДКА ПАТОМСКОГО КОНУСА 2012

Early Holocene (8.6 ka) rock avalanche deposits, Obernberg valley (Eastern Alps): Landform interpretation and kinematics of rapid mass movement

Early Holocene (8.6 ka) rock avalanche deposits, Obernberg valley (Eastern Alps): Landform interpretation and kinematics of rapid mass movement

• Marc Ostermann^{a, ,} Этот e-mail адрес защищен от спам-ботов, для его просмотра у Вас должен быть включен Javascript ,
• Diethard Sanders^a,
• Susan Ivy-Ochs^{b, c},
• Vasily Alfimov^c,
• Manfred Rockenschaub^d,
• Alexander Römer^d

• ^a Institute for Geology and Palaeontology, University of Innsbruck, A-6020 Innsbruck, Austria
• ^b Department of Geography, University of Zurich, CH-8057 Zurich, Switzerland
• ^c Laboratory of Ion Beam Physics, ETH Zurich, CH-8093 Zurich, Switzerland
• ^d Geological Survey of Austria, A-1030 Vienna, Austria

1. Introduction

Rockslides and rock avalanches include gravity-driven, rapid slope failures that are larger than about 10⁵ to 10⁶ m³ in volume (Evans et al., 2006). Most rock avalanches post-dating the Last Glacial Maximum (LGM) in the Alps are readily recognized by their shape and size as well as by an extremely poorly sorted composition ranging from cataclastic gouge to megablocks ( [Pollet and Schneider, 2004] and [Crosta et al., 2007]). At a few locations, however, the interpretation of landforms composed of very poorly sorted deposits remains controversial. For instance, transverse and lateral ridges of rock avalanches may appear similar to terminal and lateral moraines of glaciers. Diamicts of fine-grained matrix hosting polished and striated rock fragments may, either, represent basal till, or may form in rock avalanches. In addition, rock avalanches can flow out over long distances, which may promote confusion with glacial sediments (cf. Hewitt, 1999).

In the Obernberg valley, Austria, the character of a rock avalanche deposit led to diverse interpretations for more than a hundred years. In its distal part, which is about 2 km in length, the avalanche mass shows a regular arrangement of ridges and hillocks that are roughly transversal to valley axis. Frech (1903), who first investigated these deposits, interpreted their entirety as a rock avalanche. Paschinger (1953) agreed, but interpreted the ridges as a result of decay of underlying glacial ice. Later, based solely on the morphology of ridges and hillocks, the landforms were thought to be terminal moraines and kames ( [Magiera, 2000], [Ebner et al., 2003] and [Wastl, 2007]). Herein, we present a survey based on field investigations, volume estimation using airborne laser scanning image, a digital elevation model and electrical tomography, and proxy event ages produced by radiocarbon and cosmic ray-exposure dating. Our results indicate that the purported glacial landforms accumulated from a rock avalanche 8.6 ± 0.6 ka ago. We discuss: (a) a potential relation of rock avalanching with the 8.2-ka climatic phase in the Alps, and (b) the significance of transversal ridges with respect to rock avalanche kinematics.

2. The study area

The SW–NE trending Obernberg valley is a 9-km-long tributary of the Wipp valley, about 25 km south of Innsbruck (Fig. 1). Over most of its extent, the Wipp valley follows the Brenner extensional fault. The hangingwall of the Brenner fault consists of the Oetztal–Stubai basement complex with an overlying, parautochthonous Mesozoic succession and two superposed thrust nappes (Blaser and Steinach nappes); the footwall is comprised of variegated metamorphic successions of a different tectonostratigraphic unit (Fig. 1) (Fügenschuh et al., 1997). Neogene fission-track cooling ages in the footwall adjacent to the Brenner fault, and fault plane solutions of historical earthquakes suggest that the Brenner fault may still be active at a low rate (cf. [Fügenschuh et al., 1997], [Fügenschuh et al., 2000], [Fügenschuh and Mancktelow, 2003] and [Reiter et al., 2003]). The Obernberg rock avalanche detached from an isoclinally folded, Mesozoic series of calcitic to dolomitic marbles, calcitic phyllites and, subordinately, phyllites and quartzites (Fig. 2) (Rockenschaub et al., 2003). The dip/dip azimuth of schistosity in the isoclinally-folded series ranges from horizontal to 270–320°/10–20° (Reiser et al., 2010). The detachment scarp of the rock avalanche is located about 500 m west, and in the footwall of, an N–S striking normal fault (Portjoch fault) with a vertical throw of at least a few hundred meters. East of the Portjoch fault, the right flank of the See valley and that of the upper Obernberg valley consist mainly of quartz phyllite and mica schist of the Steinach nappe (Fig. 2 and Fig. 3). Whereas the mentioned Mesozoic series is deeply incised by many gullies, and the toes of slopes are covered with talus aprons, there is nearly no fluvial incision and talus formation within the Steinach nappe. The quartz phyllites there tend to form numerous slow moving, shallow to deep, mass movements (Fig. 3).