olelog

A glacial lake is a lake formed by the melting of glacier ice. In a time like now with global warming most glaciers on earth are retreating, resulting in more and swelling glacial lakes - lakes that are often formed behind terminal/end moraines, also known as moraine dammed glacier lakes. A serious problem with such lakes is that when the water reaches a certain level the dam will burst and an extremely large amount of water will suddenly flow into lower valleys with potential catastrophic results.

Studies of the past 30 years show that the temperatures in the Himalayas are rising up to eight times faster than the global average. Nepal has more than 2,300 glacial lakes and experts say at least 20 are in danger of bursting. One of them is the Imja Glacier above Dengboche, which is retreating by about 70 metres a year, and the melting ice has formed a huge lake that could devastate villages downstream if it bursts. The Imja lake, that was nonexistent in 1960, is now the second largest glacial lake in Nepal and is considered the most dangerous. It covers almost one square kilometre, and is estimated to hold 36 million cubic metres of water.

Information about how many people would be affected by a glacial lake bursting remains limited, but experts say the floodwaters could reach as far as Nepal's southern planes and beyond. Environment secretary Uday Raj Sharma said last week the bursting of the Imja lake would be like a "Nepalese tsunami," comparing it with the 2004 Indian Ocean disaster in which around 220,000 people died.

Global Warming - Imja Glacier - on YouTube (of November 10, 2007):

• http://www.redorbit.com/news/science/1744838/swelling_glacial_lakes_threaten_nepalese_communities/index.html?source=r_science
  
• http://www.theuiaa.org/bursting_glacial_lakes_in_nepal.html
  
• http://news.yahoo.com/s/afp/20090830/wl_sthasia_afp/nepalclimatewarminghimalayasglaciers
  
• http://www.terradaily.com/reports/Melting_glaciers_threaten_Nepal_tsunami_999.html
  
• http://www.globalpolicy.org/component/content/article/212/45218.html (2003)
  
• http://www.youtube.com/watch?v=4OOfOY0zfcA (20070
  

A 6.8-magnitude quake occurred in the Banda Sea, Indonesia, on Friday 28 August at 09:51 local time. It caused no severe damage, and although it was under sea it triggered no tsunami.

If you wonder why? the answer is simple, it was far too deep. And by deep I mean really deep - at a depth of 633.2 km. It is about as deep as earthquakes go. The deepest earthquake ever recorded is 705 km deep, under the Fiji Islands in the Southwest Pacific, on 6 May 2007.

Such deep earthquakes only occur in subduction zones - and only in some old subduction zones.



Looking at a map of historic seismicity from USGS we can see that the quake occurred in a band of former deep earthquakes (marked in red) at a certain distance from the surface frontier of the subduction zone marked as a purple line. In this area it is in fact relatively easy (even though the plate tectonics in the area are rather complex) to follow the inclination of the Benioff zone from shallow earthquakes, 0 – 36 km deep, to the deepest earthquakes 500 – 800 km deep. The earthquake foci normally plot along a dipping plane at an angle of 33 to 60 degrees and such a plane is called a Benioff zone. Earthquakes along Benioff zones define a lithospheric plate that descends into the mantle beneath another, overlying plate. The zone is named after Hugo Benioff, a US seismologist who first described this feature.

• http://www.etaiwannews.com/etn/news_content.php?id=1043099&lang=eng_news
  
• http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009kwae.php#details
  
• http://my.opera.com/nielsol/blog/2007/05/09/deep-fiji-eartquake
  

In Danish:

• http://www.dr.dk/Nyheder/Udland/2009/08/28/061109.htm?rss=true
  

A team of a dozen scientists now report new in situ observations and laboratory studies of specimens of a small (diameter 2.4–7.5 cm) strikingly hexagonal form originally described from sedimented steps in a wall of the axial valley of the Mid-Atlantic Ridge (water depth 3430–3575 m) near 26°N, 45°W that appears to be identical to the iconic form Paleodictyon nodosum described as a trace fossil from Eocene flysch deposits at sites in Europe and Wales.


(This photo of Paleodictyon is from the Benkovac Stone Unit. The Late Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. The Eocene was an epoch from ca. 56 - 34 million years ago.)

The team has gathered enough evidence to prove that the organism represents one of the world’s oldest living fossils, perhaps the oldest. The ancestors of the creature, Paleodictyon nodosum, go back to the dawn of complex life. And the creature itself, known from fossils, was once thought to have gone extinct some 50 million years ago.

So far it has not been possible to capture one of the creatures alive. It thrives in restricted areas of Atlantic seabed. Its only visible feature consists of tiny holes arranged in six-sided pattern. Until the real creature has been caught the scientists still vigorously debate what it is. The main question is whether the hexagonal patterns are burrows or body parts, vacant residences or animal remains.

The new paper seeks no consensus on the question of whether the holes and subsurface networks represent burrows or body parts. Dr. Seilacher, who backs the burrow idea, sees the tunnels as a kind of farm where an unknown type of worm or other organism raises micro-organisms to eat, while Dr. Rona sees the holes as body parts, perhaps from a type of compressed sponge. The lack of biological clues, he said in an interview, may arise because microbial predators eat the remains after the creatures die.

Reference:
Rona et al.
Paleodictyon nodosum: A living fossil on the deep-sea floor
doi:10.1016/j.dsr2.2009.05.015
(Article in Press)

• http://www.nytimes.com/2009/08/25/science/25fossil.html
  
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGC-4WD1BWS-4&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=989443494&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=900183d12bc1802d8470f85e1b961b5b
  
• http://my.opera.com/nielsol/blog/2008/11/03/tracefossils-paleodictyon
  
  

I have just read a post that I would like to have written - but didn’t.

Nitish Priyadarshi at “Environment and Geology” did, and I am delighted to recommend his post, where he tells how economic deposits are associated with terrestrial impact structures.

Over to:

• http://nitishpriyadarshi.blogspot.com/2009/08/are-impact-craters-useful.html
  

Reading a thesis is not done in half an hour. Struggling my way through a new interesting thesis by Christin Eriksson at the Department of Earth Sciences, University of Gothenburg, on the "Characterizing and Reconstructing 500 years of Climate in the Baltic Sea Basin” I got stuck during the paragraph about the geologic history of the Baltic Sea (reminding me of some of the material I read 30-40 years ago. To refresh my memory I have dived into some of the articles on Wikipedia and a few of my old books to refresh my memory.

Before the Baltic sea there was the Eemian sea, a body of water located approximately where the Baltic sea is now during the last or Eemian Stage (of the Ice Age), roughly 130,000 to 115,000.

The not-so-long history of the Baltic Sea starts, however, about 15,000 years ago with the formation of the Baltic Ice Lake, 15,000–11,600 years ago - so The Baltic Sea is one of the youngest on the Earth. During each ice-sheet advance, the Baltic area was strongly eroded. It resulted in the formation of a vast depression, occupied today by the Baltic Sea.

Large ice sheets that had been dominating the region for several thousand years were now retreating rapidly, leaving behind suppressed land and discharging large amounts of freshwater. The map shows Late Baltic Ice Lake around 10,300 years ago, with a channel near Mount Billingen through what is now central Sweden. (Map of the Early Baltic Ice Lake, about 13,000 years ago is found here).

Clays, deposited in the Baltic Ice Lake, are conspicuous by alternating light-coloured coarser-grained layers and darker finer-grained layers. The former were deposited in summers, the latter – in winters. These deposits contain small amount of organic matter.

The Baltic Ice Lake was soon replaced by the Yoldia Sea, which lasted for approximately 900 years. At this stage, a connection with the outside ocean was established near Närke and Vänern, situated just south of the retreating ice sheet. The name of the sea is adapted from the obsolete name of the bivalve, Portlandia arctica (previously known as Yoldia arctica), found around Stockholm. This bivalve requires cold saline water. In the initial phase of the Yoldia Sea saline water poured into the Baltic, before the acceleration of glacial melting.

The connection with the ocean later closed as the Yoldia Sea was replaced by the Ancylus Lake, and a freshwater system now came into being. The map shows the Ancylus Lake around 8,700 years ago. The relic of Scandinavian Glacier in white. The river Svea älv formed an outlet to the Atlantic Sea. Salt water did not enter the lake, which became entirely fresh as the lake rose above sea level. The ancylus lake is named after the freshwater limpet Ancylus fluviatilis.

Deeper parts of the Yoldia Sea and Ancylus Sea were areas of fine-grained clay deposition with infrequent faunal fragments.

Towards the end of its history the level of the Ancylus Lake was falling following the formation of a new outlet at the Great Belt. The Ancylus Lake reached the level of the sea ca. 8500 years ago, marking the beginning of the Mastogloia Sea. Many researchers have been unwilling to recognize the Mastogloia Sea as a separate stage in the development of the Baltic Sea, favouring including it in either the Ancylus Lake stage or the Littorina Sea stage. The transitional Mastogloia Sea was so named because it was inhabited by characteristic diatoms of the genus Mastogloia.

The Littorina Sea (also Litorina Sea) later followed, when a connection with the outside ocean was reopened approximately 8500 years ago, due to the great sea level rise resulting from melting ice sheets. The wide and deep straits in the south (the so-called “Dana Elv” which as one of Europe’s water-richest rivers flew through the deep channel of the Great Belt) allowed for extensive water exchange with the North Atlantic, and the salinity of the Littorina Sea was higher than the Baltic Sea as we know it today. It existed around 7500–4000 years ago and followed the Mastogloia Sea. The Littorina Sea was a period of transgression and maximum salinity during the warmer Atlantic period of European climatology. At the optimum, approximately 4500 years ago, the sea contained twice the volume of water and covered 26.5% more surface area than it does today. The map shows the Littorina Sea around 7000 years ago.

Silt deposits, accumulated at that time in deeper waters, contain abundant fragments of marine microfauna and microflora. Shallow water sand deposits are abound in marine bivalves of Cardium sp. and Macoma balthica.


The transgression phase of the Littorina Sea continued for approximately 3000 years in its southern parts, caused by a rapid sea level change that dominated the isostatic uplift (following the Ice Age). When the sea level rise ended, the land uplift in Sweden and areas north of Lithuania caused regression of the Baltic Sea, resulting in shallower sills and thereby reduced Atlantic inflows. Even today, the land is still recovering from the last glaciation, and isostatic maps indicate that Sweden is experiencing isostatic uplift in the north and isostatic depression in the south.

Now if you want to know more about the latest 500 years of the Baltic Sea you may read the interesting thesis (I still haven’t got to the end of it!).

• http://www.sciencedaily.com/releases/2009/08/090812092817.htm
  
• http://www.pgi.gov.pl/pgi_en/index.php?option=news&task=viewarticle&sid=4&Itemid=2
  
  

In Swedish:

• http://www.science.gu.se/aktuellt/nyheter/Nyheter+Detalj/Snabba_forandringar_i_vinterklimatet.cid888189