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Sunday, 15. February 2009, 19:04:13
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Solonker Suture Zone
Monday, 14. December 2009, 20:36:57
A “suture zone” is the area where two continental plates have joined together through continental collision.
The Solonker suture zone marks the final closure of the Paleo-Asian ocean during the convergence of the North China and the Siberian Plate, that I mentioned in a post last week.
Several authors acknowledge, however, that the tectonic development of the Solonker suture is poorly understood. The term "Solonker” was defined by Sengör and colleagues in 1993 and further in 1996. It is Named after Solonker in Mongolia and it extends roughly from Solonker, via Sonidzuoqi and Xilinhot of Inner Mongolia, further east to Northeast China. Two belts are recognized along the suture zone: an older, deformed subduction-related magmatic belt, represented by the Baiyinbaolidao arc complex, and a younger, collision-related granite belt, represented by the Halatu granitic plutons.
Plate reconstructions do not fully agree on this part of the world, made difficult by all sorts of terranes accreted in the zone, during continental collision. One of the reconstructions has made it to wikipedia under the Paleo-Tethys Ocean - with an image from the PhD thesis of Pierre Dèzes (1999; Institut de Mineralogie et Petrographie, Université de Lausanne). This image shows a reconstruction of the tectonic plate about 290 million years ago. Here I am showing a part of the image:
Solonker is here shown between the Siberia plate and the North China plate (also known as North China Block or North China Craton). In this reconstruction the Paleo-Asian ocean is clearly not shown to be a part of the Paleothytus. In the reconstruction I showed you a few days ago from the late Devonian the two oceans seemed to be connected:
The Paleo-Tethys Ocean closed off about 290 - 180 million years ago.
The Solonker Suture zone is treated in several papers. Here i shall only mention two relatively recent paper freely available as pdf files on the internet:
Boris A. Natal’in
Istanbul Technical University, Istanbul, Turkey
Tectonic evolution of Mongolia, Northeastern China, and Southeastern Russia in the Paleozoic and early Mesozoic
from The Third International Workshop and Field Excursion For IGCP-480, Beijing (China), 6-15, Aug. 2007
(http://www.igcp.itu.edu.tr/Publications/China07/Natalin_07.pdf)
and more recent
Chen et al.
Evolution of the Solonker suture zone: Constraints from zircon U–Pb ages, Hf isotopic ratios and whole-rock Nd–Sr isotope compositions of subduction-and collision-related magmas and forearc sediments
Journal of Asian Earth Sciences 34 (2009) 245–257
(http://www.earth.sinica.edu.tw/papers/JahnBM/Chen%20et%20al%202009%20JAES%20Solonker%20suture.pdf)
Other suture zones, which I have posted posted about:
South-Anyui suture (with map).
Tornqvist zone (with maps).
The Solonker suture zone marks the final closure of the Paleo-Asian ocean during the convergence of the North China and the Siberian Plate, that I mentioned in a post last week.
Several authors acknowledge, however, that the tectonic development of the Solonker suture is poorly understood. The term "Solonker” was defined by Sengör and colleagues in 1993 and further in 1996. It is Named after Solonker in Mongolia and it extends roughly from Solonker, via Sonidzuoqi and Xilinhot of Inner Mongolia, further east to Northeast China. Two belts are recognized along the suture zone: an older, deformed subduction-related magmatic belt, represented by the Baiyinbaolidao arc complex, and a younger, collision-related granite belt, represented by the Halatu granitic plutons.Plate reconstructions do not fully agree on this part of the world, made difficult by all sorts of terranes accreted in the zone, during continental collision. One of the reconstructions has made it to wikipedia under the Paleo-Tethys Ocean - with an image from the PhD thesis of Pierre Dèzes (1999; Institut de Mineralogie et Petrographie, Université de Lausanne). This image shows a reconstruction of the tectonic plate about 290 million years ago. Here I am showing a part of the image:
Solonker is here shown between the Siberia plate and the North China plate (also known as North China Block or North China Craton). In this reconstruction the Paleo-Asian ocean is clearly not shown to be a part of the Paleothytus. In the reconstruction I showed you a few days ago from the late Devonian the two oceans seemed to be connected:The Paleo-Tethys Ocean closed off about 290 - 180 million years ago.
The Solonker Suture zone is treated in several papers. Here i shall only mention two relatively recent paper freely available as pdf files on the internet:
Boris A. Natal’in
Istanbul Technical University, Istanbul, Turkey
Tectonic evolution of Mongolia, Northeastern China, and Southeastern Russia in the Paleozoic and early Mesozoic
from The Third International Workshop and Field Excursion For IGCP-480, Beijing (China), 6-15, Aug. 2007
(http://www.igcp.itu.edu.tr/Publications/China07/Natalin_07.pdf)
and more recent
Chen et al.
Evolution of the Solonker suture zone: Constraints from zircon U–Pb ages, Hf isotopic ratios and whole-rock Nd–Sr isotope compositions of subduction-and collision-related magmas and forearc sediments
Journal of Asian Earth Sciences 34 (2009) 245–257
(http://www.earth.sinica.edu.tw/papers/JahnBM/Chen%20et%20al%202009%20JAES%20Solonker%20suture.pdf)
Other suture zones, which I have posted posted about:
South-Anyui suture (with map).
Tornqvist zone (with maps).
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Closure of Paleoasian Ocean 251 Million Years Ago
Wednesday, 9. December 2009, 16:50:13
Oceans come and go. Long ago an ocean existed between Siberia and North China, known by geologists as the Paleoasian Ocean. It probably opened about 900 million years ago - according to Dobretsov et al. (2003) the opening occurred 970-850 million years ago.
Here is a very rough global plate tectonic reconstruction from late Devonian - that would be towards 360 million years ago (after Wikipedia).
But when did this ocean close? - or in other words, when did the Siberian Plate and the North China Plate finally collide to form the Eurasian continent. Deng Shenghui and colleagues present what they take to be the answer in a paper newly published in Science in China (2009, vol.52).
During the Carboniferous and Early Permian (about 360-270 million year ago), the North China plate was located near the equator, where subtropic-tropic type of flora grew, named as "the Cathaysia Flora". In contrast, the Siberian plate was located at high latitude, where temperate flora was distributed, known as "the Angara Flora". These two types of floras are very distinctive and did not mix with each other because of the geological barrier and their separate niches in different climatic zones.
Based on their study of land plant fossils Deng et al. concluded that the Paleoasian Ocean disappeared at the end of the Permian, about 251 million years ago. They argue that the Paleoasian Ocean, once a barrier of plant immigration, must have disappeared in the Late Permian, because at that time plants that previously grew in North Chin now immigrated to Siberia.
Unfortunately I have not been able to put my hands on the paper - it is NOT open access! - But here is the reference for the fortunate ones:
Reference:
Deng S H, Wan C B, Yang J G. 2009.
Discovery of a Late Permian Angara-Cathaysia mixed flora from Acheng of Heilongjiang, China, with discussions on the closure of the Paleoasian Ocean.
Science in China, Series D：Earth Science, vol. 52, no.11: 1746-1755.
Here is a very rough global plate tectonic reconstruction from late Devonian - that would be towards 360 million years ago (after Wikipedia).
But when did this ocean close? - or in other words, when did the Siberian Plate and the North China Plate finally collide to form the Eurasian continent. Deng Shenghui and colleagues present what they take to be the answer in a paper newly published in Science in China (2009, vol.52).
During the Carboniferous and Early Permian (about 360-270 million year ago), the North China plate was located near the equator, where subtropic-tropic type of flora grew, named as "the Cathaysia Flora". In contrast, the Siberian plate was located at high latitude, where temperate flora was distributed, known as "the Angara Flora". These two types of floras are very distinctive and did not mix with each other because of the geological barrier and their separate niches in different climatic zones.
Based on their study of land plant fossils Deng et al. concluded that the Paleoasian Ocean disappeared at the end of the Permian, about 251 million years ago. They argue that the Paleoasian Ocean, once a barrier of plant immigration, must have disappeared in the Late Permian, because at that time plants that previously grew in North Chin now immigrated to Siberia.
Unfortunately I have not been able to put my hands on the paper - it is NOT open access! - But here is the reference for the fortunate ones:
Reference:
Deng S H, Wan C B, Yang J G. 2009.
Discovery of a Late Permian Angara-Cathaysia mixed flora from Acheng of Heilongjiang, China, with discussions on the closure of the Paleoasian Ocean.
Science in China, Series D：Earth Science, vol. 52, no.11: 1746-1755.
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http://www.terradaily.com/reports/Paleoasian_Ocean_Disappeared_About_251_Million_Years_Ago_999.html
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http://www.physorg.com/news179497040.html
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http://www.eurekalert.org/pub_releases/2009-12/sicp-sol120709.php
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Polar Deserts - Dry Valleys, Antarctica
Tuesday, 8. December 2009, 16:42:23
Deserts are dry and arid - but not necessarily hot, or situated in the tropics or subtropics. Lack of precipitation (often combined with excess evaporation) is what makes them, well, deserts. Deserts take up about one third (33%) of the Earth's land surface. It may also surprise you that sand covers only about 20% of Earth's deserts.
Polar deserts are areas with annual precipitation less than 250 millimeters and a mean temperature during the warmest month of less than 10°C. Polar deserts on the Earth cover nearly 5 million km2 and are mostly bedrock or gravel plains. Sand dunes are not prominent features in these deserts, but snow dunes occur commonly in areas where precipitation is locally more abundant. Temperature changes in polar deserts frequently cross the freezing point of water. This "freeze-thaw" alternation forms patterned textures on the ground, as much as 5 meters in diameter.
(Image courtesy of USGS Image Processing Facility. Flagstaff. Arizona)
The Dry Valleys of Antarctica have been ice-free for thousands of years. The Dry Valleys are swept free of snow by nearly relentless katabatic winds—cold, dry air that rolls downhill toward the sea from the high altitudes of the ice sheet.
Examples of katabatic winds: the Santa Ana in southern California, and the Bora in the Adriatic. Katabatic is derived from the Greek word katabatikos meaning "going downhill".
The Dry valleys is one of the world's most extreme deserts. They are a series of parallel valleys situated between the Ross Sea and the East Antarctic Ice Sheet. The valleys cut through the Beacon sandstone. The gravel appears to be derived from two sources. The first is terminal moraines which have formed at the end of glaciers which descend into the Dry Valleys. These glaciers sublime directly to air, for the most part, adding very little liquid water to the valleys. The second potential source of gravel is a rather unusual source. It is believed that during some glacial periods, the quantity of ice in the nearby Ross Sea was so great that it forced its way inland into some of the Dry Valleys, in a kind of reverse glacier and deposited its own terminal moraine.
Polar deserts are areas with annual precipitation less than 250 millimeters and a mean temperature during the warmest month of less than 10°C. Polar deserts on the Earth cover nearly 5 million km2 and are mostly bedrock or gravel plains. Sand dunes are not prominent features in these deserts, but snow dunes occur commonly in areas where precipitation is locally more abundant. Temperature changes in polar deserts frequently cross the freezing point of water. This "freeze-thaw" alternation forms patterned textures on the ground, as much as 5 meters in diameter.
(Image courtesy of USGS Image Processing Facility. Flagstaff. Arizona)
The Dry Valleys of Antarctica have been ice-free for thousands of years. The Dry Valleys are swept free of snow by nearly relentless katabatic winds—cold, dry air that rolls downhill toward the sea from the high altitudes of the ice sheet.
Examples of katabatic winds: the Santa Ana in southern California, and the Bora in the Adriatic. Katabatic is derived from the Greek word katabatikos meaning "going downhill".
The Dry valleys is one of the world's most extreme deserts. They are a series of parallel valleys situated between the Ross Sea and the East Antarctic Ice Sheet. The valleys cut through the Beacon sandstone. The gravel appears to be derived from two sources. The first is terminal moraines which have formed at the end of glaciers which descend into the Dry Valleys. These glaciers sublime directly to air, for the most part, adding very little liquid water to the valleys. The second potential source of gravel is a rather unusual source. It is believed that during some glacial periods, the quantity of ice in the nearby Ross Sea was so great that it forced its way inland into some of the Dry Valleys, in a kind of reverse glacier and deposited its own terminal moraine.
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http://www.redorbit.com/images/images-of-the-day/img/27356/dry_valleys_antarctica/index.html?source=r_earthiod
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http://www.nasa.gov/multimedia/imagegallery/image_feature_1536.html
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http://www.antarcticconnection.com/antarctic/science/dryvalleys.shtml
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http://en.wikipedia.org/wiki/McMurdo_Dry_Valleys
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http://www.gdargaud.net/Antarctica/DryValleys.html
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http://earthobservatory.nasa.gov/IOTD/view.php?id=35535
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Malawi Earthquake
Monday, 7. December 2009, 16:11:55
Malawi is within the most seismically active belt of the East African Rift System. The area is characterised by moderate magnitude earthquakes (M ≤ 6.0). Historical records show strongly felt earthquakes reported in various parts of the country, but no damage to property or loss of life had been recorded until the occurrence of the 1989 Salima Earthquake which claimed at least 9 lives, injured 100 people, another 50,000 homeless, and damaged some property.
The U.S. Geological Survey reported four earthquakes measuring between 5.1 and 5.8 on in the hour to 1829 GMT on Sunday 6 December 2009 in the Karonga district north of Malawi.
A few people were injured.
Lake Nyasa, also known as Lake Malawi, lies in the rift valley with escarpments formed by fault lines on both the west and east sides. If you compare the Google map, where I have marked the earthquake, with my sketch map, you will see that the earthquake occurred at one of the major faults in the area.
PS:
Earth tremors hit Malawi for a second day on Monday 7 December 2009 and police said at least six people had been injured, two seriously, and buildings damaged in the uranium-rich northern Karonga district.
PS of Tuesday 8 November 2009:
For a third day the same area was hit, this time by a shallow (10 km) magnitude 5.9 earthquake (at 05:08:57 AM at epicenter).
The U.S. Geological Survey reported four earthquakes measuring between 5.1 and 5.8 on in the hour to 1829 GMT on Sunday 6 December 2009 in the Karonga district north of Malawi.
A few people were injured.
Lake Nyasa, also known as Lake Malawi, lies in the rift valley with escarpments formed by fault lines on both the west and east sides. If you compare the Google map, where I have marked the earthquake, with my sketch map, you will see that the earthquake occurred at one of the major faults in the area.-
http://www.alertnet.org/thenews/newsdesk/GEE5B50IA.htm
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http://www.gdacs.org/reports.asp?eventType=EQ&ID=70558&system=asgard&location=MWI&alertlevel=Orange&glide_no=
PS:
Earth tremors hit Malawi for a second day on Monday 7 December 2009 and police said at least six people had been injured, two seriously, and buildings damaged in the uranium-rich northern Karonga district.
PS of Tuesday 8 November 2009:
For a third day the same area was hit, this time by a shallow (10 km) magnitude 5.9 earthquake (at 05:08:57 AM at epicenter).
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Linear Dunes
Monday, 7. December 2009, 09:04:57
No, I am not talking COP15 today - everybody else is. Let me stick to anything else, like linear dunes. Linear dunes may be more than 160 kilometers long. Linear dunes may occur as isolated ridges, but they generally form sets of parallel ridges separated by miles of sand, gravel, or rocky interdune corridors.
scale = 5 km
Vast, windswept plains of sand dunes (ergs), occasionally interrupted by rocky outcrops, stretch across much of Algeria. Except for exceedingly rare oases, these seas of sand are usually as good as empty of life, including humans (well I have seen snakes out there, so there must be something to eat - now and then.
This natural-color image from the Landsat 5 satellite shows the emptiness of the Erg Iabès in western Algeria’s Adrar province (with Adrar as capital). Adrar, a Berber word meaning "mountain", is by the way the name of several areas in Northwest Africa. This rather small erg (compared to the country’s Grand Ergs) occupies the wide gap between the El Eglab Massif to the west and the Tademaït Plateau to the northeast.
Long, linear dunes such as the ones pictured here align in the direction of the prevailing winds, and they usually form under the influence of strong winds. However, linear dunes are not the only types of dunes that are found in ergs. For example, weaker winds blowing over a linear dune in the non-prevailing wind direction may create star dunes. Barchan dunes are shaped like a crescent, with a more gradual slope on the windward side, and a steeper slope on the downwind side.
scale = 5 km
Vast, windswept plains of sand dunes (ergs), occasionally interrupted by rocky outcrops, stretch across much of Algeria. Except for exceedingly rare oases, these seas of sand are usually as good as empty of life, including humans (well I have seen snakes out there, so there must be something to eat - now and then.
This natural-color image from the Landsat 5 satellite shows the emptiness of the Erg Iabès in western Algeria’s Adrar province (with Adrar as capital). Adrar, a Berber word meaning "mountain", is by the way the name of several areas in Northwest Africa. This rather small erg (compared to the country’s Grand Ergs) occupies the wide gap between the El Eglab Massif to the west and the Tademaït Plateau to the northeast.
Long, linear dunes such as the ones pictured here align in the direction of the prevailing winds, and they usually form under the influence of strong winds. However, linear dunes are not the only types of dunes that are found in ergs. For example, weaker winds blowing over a linear dune in the non-prevailing wind direction may create star dunes. Barchan dunes are shaped like a crescent, with a more gradual slope on the windward side, and a steeper slope on the downwind side.
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Phoenix Tectonic Plate
Sunday, 6. December 2009, 14:16:48
It is of great help that Google Maps is now covering the bottom of the oceans as well. A quick look at the area in the Drake Passage between the southern tip of South America and the northern tip of Antarctica may make you suspicious. Do we see a tectonic plate bordered by two fracture zones, a subduction zone and a spreading ridge? It looks like it.
Drake Passage between the South America and Antarctic Peninsular opened during the development of the Scotia Arc from about 41 million years ago. In Drake Passage, the Phoenix Ridge has three extinct spreading ridge segments (P1, P2 and P3 in the figure below). These segments separated the Phoenix plate from the Antarctic plate. Previous magnetic studies suggested that the seafloor spreading in each of the ridge segments stopped at the same time about 3.3 million years ago. The figure below is taken from a study published as U.S.Geological Survey and The National Academies; USGS OF-2007-1047, Extended Abstract 110, and available for download as PDF file: http://pubs.usgs.gov/of/2007/1047/ea/of2007-1047ea110.pdf
The figure cover approximately the same area, and I hope you can recognise the same features as seen in the Google map above. There are plenty of parallel fracture zones in the area. Of importance here are the Shackleton Fracture Zone (SFZ) and the Hero Fracture Zone (HFZ) (bordering two sides of the Phoenix Plate). SST finally is The South Shetland Trench northwest of the South Shetland Islands. It is the only trench along the Pacific margin of the Antarctic Peninsula. Subduction here almost stopped after the cessation of spreading in Drake Passage about 3.3 million years ago. The red lines are survey lines from the mentioned study (so just ignore them).
The Phoenix Plate is also known as the Aluk Plate. It was an ancient tectonic plate that existed during the mid-Cretaceous through early Tertiary time. The Phoenix Plate began subducting under the Antarctic Plate. The Phoenix Ridge is a mid-oceanic ridge between the Pacific and the Phoenix Plates which had a spreading rate of 18-20 cm per year until around 84 million years ago. A major decrease in spreading rate, and the convergence rate with the Antarctic Plate occurred around 52.3 million years ago. Today the Phoenix Plate is part of the Pacific Plate, as the spreading ridge, the Hero Fracture Zone and the South Shetland subduction zone are no longer active. The only movement now is along the Shackleton fracture Zone (active boundary).
The book Antarctica has a lot more to tell about this area. Here is an illustration from page 272.
Unfortunately it is rather expensive! ($199 at Amazon.com).
This post may be seen as a continuation on my post on the Scotia Plate.
Talking about Antarctica - Alessia Maggi of Sismordia is ready for her third Antarctic summer campaign. I and a lot of other fans will certainly follow her via her blog.
PS:
The Phoenix Plate is also known as the Drake Plate.
Drake Passage between the South America and Antarctic Peninsular opened during the development of the Scotia Arc from about 41 million years ago. In Drake Passage, the Phoenix Ridge has three extinct spreading ridge segments (P1, P2 and P3 in the figure below). These segments separated the Phoenix plate from the Antarctic plate. Previous magnetic studies suggested that the seafloor spreading in each of the ridge segments stopped at the same time about 3.3 million years ago. The figure below is taken from a study published as U.S.Geological Survey and The National Academies; USGS OF-2007-1047, Extended Abstract 110, and available for download as PDF file: http://pubs.usgs.gov/of/2007/1047/ea/of2007-1047ea110.pdf
The figure cover approximately the same area, and I hope you can recognise the same features as seen in the Google map above. There are plenty of parallel fracture zones in the area. Of importance here are the Shackleton Fracture Zone (SFZ) and the Hero Fracture Zone (HFZ) (bordering two sides of the Phoenix Plate). SST finally is The South Shetland Trench northwest of the South Shetland Islands. It is the only trench along the Pacific margin of the Antarctic Peninsula. Subduction here almost stopped after the cessation of spreading in Drake Passage about 3.3 million years ago. The red lines are survey lines from the mentioned study (so just ignore them).
The Phoenix Plate is also known as the Aluk Plate. It was an ancient tectonic plate that existed during the mid-Cretaceous through early Tertiary time. The Phoenix Plate began subducting under the Antarctic Plate. The Phoenix Ridge is a mid-oceanic ridge between the Pacific and the Phoenix Plates which had a spreading rate of 18-20 cm per year until around 84 million years ago. A major decrease in spreading rate, and the convergence rate with the Antarctic Plate occurred around 52.3 million years ago. Today the Phoenix Plate is part of the Pacific Plate, as the spreading ridge, the Hero Fracture Zone and the South Shetland subduction zone are no longer active. The only movement now is along the Shackleton fracture Zone (active boundary).
The book Antarctica has a lot more to tell about this area. Here is an illustration from page 272.
Unfortunately it is rather expensive! ($199 at Amazon.com).
This post may be seen as a continuation on my post on the Scotia Plate.
Talking about Antarctica - Alessia Maggi of Sismordia is ready for her third Antarctic summer campaign. I and a lot of other fans will certainly follow her via her blog.
PS:
The Phoenix Plate is also known as the Drake Plate.
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Lake Atitlan Follow-up
Saturday, 5. December 2009, 15:11:02
A few days ago I published a post on Lake Atitlan based on an image from Earth Observatory (NASA)
They have just published another image of Lake Atitlan.
Harmful blue-green algae rose to the surface of Guatemala’s Lake Atitlán in October and November 2009. The green scum swirls across the surface of the lake in filaments in this photo-like image taken by NASA’s EO-1 satellite on November 27. The straight dark lines that cut through the bloom are probably the wakes of boats leaving or traveling to the city of Panajachel. A few boats are visible as tiny white dots on the surface of the lake.
Blue-green algae, or cyanobacteria, are single-celled organisms that rely on photosynthesis to turn sunlight into food. The bacteria grow swiftly when nutrients like phosphorus and nitrogen concentrate in still water. According to local news reports, the nutrients feeding the bloom in Lake Atitlán come from sewage, agricultural run off, and increased run off as a result of deforestation around the lake basin.
Something must urgently be done to limit or eliminate the run-off and sewage that enters the lake so future blooms can’t develop.
There is a website dedicated to Lake Atitlan, Guatemala: http://www.atitlan.net/ , and a related Twitter account: https://twitter.com/lakeatitlan
I have visited a few of their tweeted URL’s, including:
Time - http://www.time.com/time/world/article/0,8599,1942501,00.html
Vista el Mar - http://www.vistaalmar.es/content/view/875/205/
Carpe Diem Blog - http://luisfi61.blogspot.com/2009/11/la-tragedia-de-atitlan.html
La tragedia de Atitlan - also in Spanish
http://globalgeopolitics.net/wordpress/2009/11/25/environment-guatemala-sos-from-lake-atitln/
and
http://www.ipsnews.net/news.asp?idnews=49392
With a good summary of the Atitlan pollution problem
ENVIRONMENT-GUATEMALA: SOS from Lake Atitlán
A thick, chocolate-coloured scum floats on the normally clear blue waters of Lake Atitlán, in the southwestern Guatemalan province of Sololá, caused by agricultural fertilisers and untreated sewage from surrounding villages and farms.
....
If you are interested follow them on Twitter, or just have a peek.
....
Furthermore this blog http://savelakeatitlan.blogspot.com/ is dedicated to links about the lake (Save Lake Atitlan! in both English and Spanish)
They have just published another image of Lake Atitlan.
Harmful blue-green algae rose to the surface of Guatemala’s Lake Atitlán in October and November 2009. The green scum swirls across the surface of the lake in filaments in this photo-like image taken by NASA’s EO-1 satellite on November 27. The straight dark lines that cut through the bloom are probably the wakes of boats leaving or traveling to the city of Panajachel. A few boats are visible as tiny white dots on the surface of the lake.
Blue-green algae, or cyanobacteria, are single-celled organisms that rely on photosynthesis to turn sunlight into food. The bacteria grow swiftly when nutrients like phosphorus and nitrogen concentrate in still water. According to local news reports, the nutrients feeding the bloom in Lake Atitlán come from sewage, agricultural run off, and increased run off as a result of deforestation around the lake basin.
Something must urgently be done to limit or eliminate the run-off and sewage that enters the lake so future blooms can’t develop.
There is a website dedicated to Lake Atitlan, Guatemala: http://www.atitlan.net/ , and a related Twitter account: https://twitter.com/lakeatitlan
I have visited a few of their tweeted URL’s, including:
Time - http://www.time.com/time/world/article/0,8599,1942501,00.html
In his 1934 travel book “Beyond the Mexique Bay”, Aldous Huxley ... wrote, ... Atitlan, ... "is Como with the additional embellishment of several immense volcanoes. It is really too much of a good thing." ...
Atitlan is indeed breathtaking, but nowadays it is leaving many visitors gasping for breath. A thick brown sludge is tarnishing its once blue waters. It is the result of decades of ecological imbalance, brought on by economic and demographic pressures. The unsightly and smelly layer, more than 100 feet deep in some areas, is chasing tourists away from Mayan towns in the area and posing huge cleanup expenses to a government already strapped for cash.
Vista el Mar - http://www.vistaalmar.es/content/view/875/205/
Atitlán, SOS por el lago más bello del mundo (my translation: SOS for the most beautiful lake in the world) - also with photos for those who do not read Spanish.
Carpe Diem Blog - http://luisfi61.blogspot.com/2009/11/la-tragedia-de-atitlan.html
La tragedia de Atitlan - also in Spanish
http://globalgeopolitics.net/wordpress/2009/11/25/environment-guatemala-sos-from-lake-atitln/
and
http://www.ipsnews.net/news.asp?idnews=49392
With a good summary of the Atitlan pollution problem
ENVIRONMENT-GUATEMALA: SOS from Lake Atitlán
A thick, chocolate-coloured scum floats on the normally clear blue waters of Lake Atitlán, in the southwestern Guatemalan province of Sololá, caused by agricultural fertilisers and untreated sewage from surrounding villages and farms.
....
If you are interested follow them on Twitter, or just have a peek.
....
Furthermore this blog http://savelakeatitlan.blogspot.com/ is dedicated to links about the lake (Save Lake Atitlan! in both English and Spanish)
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Help to the Gulf Stream
Friday, 4. December 2009, 16:13:00
There has been some worry that the Gulf Stream might be hindered in doing its good work for north western Europe as a consequence of global warming, but now it seems that another consequence of the same global warming in another corner of the world might save its life. Unexpected help may come from the Agulhas Current.
The Agulhas Current flows down the east coast of Africa from 27°S to 40°S. It is narrow, swift, and one of the strongest ocean currents in the world. Southwest of Cape Town it abruptly turns back into the Indian Ocean. In this process huge rings of water with diameters of hundreds of kilometres are cut off at intervals of 3 to 4 months. These so-called "Agulhas Rings" carry warm and saline waters from the Indian Ocean into the Atlantic. It is known for quite some time that the Agulhas region is one of the key regions for the supply of salty waters into the Atlantic. By analyzing observational data and computers models it has been shown that this process is strengthening due to climate change in the Southern Ocean.
Westerlies in the Southern Ocean are blocking the water exchange between the Indian Ocean and the Atlantic. In the past decades, a southward shift of these westerlies has widened the corridor south of Africa for the inflow of water into the Atlantic. This trend could further intensify in the future as part of climate change.
In the Atlantic this extra amount of salty water is transported northward by the prevailing currents and could finally help to stabilize the Gulf Stream system in the northern North Atlantic. There it could act against the freshening process due to enhanced precipitation and the ice melting. Further studies are however required to prove the hypothesis.
Reference:
Biastoch et al., 2009:
Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies.
Nature, 462 (7272), doi:10.1038/nature08519.
In German:
PS: Copy and paste full German link into browser to make it work!
The Agulhas Current flows down the east coast of Africa from 27°S to 40°S. It is narrow, swift, and one of the strongest ocean currents in the world. Southwest of Cape Town it abruptly turns back into the Indian Ocean. In this process huge rings of water with diameters of hundreds of kilometres are cut off at intervals of 3 to 4 months. These so-called "Agulhas Rings" carry warm and saline waters from the Indian Ocean into the Atlantic. It is known for quite some time that the Agulhas region is one of the key regions for the supply of salty waters into the Atlantic. By analyzing observational data and computers models it has been shown that this process is strengthening due to climate change in the Southern Ocean. Westerlies in the Southern Ocean are blocking the water exchange between the Indian Ocean and the Atlantic. In the past decades, a southward shift of these westerlies has widened the corridor south of Africa for the inflow of water into the Atlantic. This trend could further intensify in the future as part of climate change.
In the Atlantic this extra amount of salty water is transported northward by the prevailing currents and could finally help to stabilize the Gulf Stream system in the northern North Atlantic. There it could act against the freshening process due to enhanced precipitation and the ice melting. Further studies are however required to prove the hypothesis.
Reference:
Biastoch et al., 2009:
Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies.
Nature, 462 (7272), doi:10.1038/nature08519.
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http://www.nature.com/nature/journal/v462/n7272/full/nature08519.html
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http://www.sciencedaily.com/releases/2009/11/091127134037.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily+%28ScienceDaily%3A+Latest+Science+News%29
In German:
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http://www.ifm-geomar.de/index.php?id=537&tx_ttnews[tt_news]=487&tx_ttnews[backPid]=1&cHash=4acf52e877
PS: Copy and paste full German link into browser to make it work!
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Scotia Tectonic Plate
Thursday, 3. December 2009, 13:29:22
A reader drew my attention to Redalyc. Redalyc is a Network that makes Scientific Journals from Latin America and the Caribbean, Spain and Portugal available for public consultation.
I dived into Geologica Acta an open access journal from Spain, where I found a paper on “Antarctic/Scotia plate convergence off southernmost Chile” in Vol .5, Nº 4, 2007, 295-306.
The paper by Polonia and Torelli is concentrated on the triple junction (black spot on map below) where relative movements between three main plates: the Antarctic, South America, and Scotia plates drive the overall tectonic setting of the southernmost Chilean margin.
There are other interesting tectonic features around the Scotia Plate, some of which i have marked in red on the map. but they are for later posts.
Reference:
Polonia and Torelli
Antarctic/Scotia plate convergence off southernmost Chile
Geologica Acta, Vol .5, Nº 4, 2007, 295-306
I dived into Geologica Acta an open access journal from Spain, where I found a paper on “Antarctic/Scotia plate convergence off southernmost Chile” in Vol .5, Nº 4, 2007, 295-306.
The paper by Polonia and Torelli is concentrated on the triple junction (black spot on map below) where relative movements between three main plates: the Antarctic, South America, and Scotia plates drive the overall tectonic setting of the southernmost Chilean margin.
There are other interesting tectonic features around the Scotia Plate, some of which i have marked in red on the map. but they are for later posts.
Reference:
Polonia and Torelli
Antarctic/Scotia plate convergence off southernmost Chile
Geologica Acta, Vol .5, Nº 4, 2007, 295-306
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http://www.geologica-acta.com/MostrarArticlesAC.do?article=gav0504
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http://earthquake.usgs.gov/earthquakes/eqarchives/poster/2006/20060820.php
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