Iceberg the size of Majorca calves from the western side of the Ronne Ice Shelf, Antarctica.

An enormous iceberg has calved from the western side of the Ronne Ice Shelf, Antarctica, according to a press release issued by the British Antarctic Survey on Friday 21 May 2021. The iceberg, newly named A-76, measures around 4320 km², and is floating in the Weddell Sea, currently making it the largest iceberg in the world. The calving is considered a natural event and not attributed to climate warming.

Iceberg A-76, which calved from the Ronne Ice Shelf, Antarctica, in May 2021. European Space Agency/Copernicus Sentinel 1.

The ‘megaberg’ was spotted by British Antarctic Survey researchers in recent images captured by the Copernicus Sentinel-1 mission on the Polar View portal. The iceberg is around 170 km in length and 25 km wide, and is slightly larger than the Spanish island of Majorca or the UK county of Somerset.

The enormity of the iceberg makes it the largest in the world, taking first place from the A-23A iceberg (approximately 3880 km² in size) which is also located in the Weddell Sea. In comparison, the A-74 iceberg that broke off the Brunt Ice Shelf, near Halley Reseach Station in February earlier this year, was only 1270 km².

The iceberg was confirmed by the US National Ice Center using Copernicus Sentinel-1 imagery. The Sentinel-1 mission consists of two polar-orbiting satellites that rely on C-band synthetic aperture radar imaging, returning data regardless of whether it is day or night, allowing year-round viewing of remote regions like Antarctica.

Icebergs are traditionally named from the Antarctic quadrant in which they were originally sighted, then a sequential number, then, if the iceberg breaks, a sequential letter.

Kaitlin Naughten, an ocean modeller at the British Antarctic Survey, explained 'Calving is an essential way for ice shelves to stay in balance. Large calving events only occur occasionally, and they can be very dramatic, but they are not necessarily a sign that the system is changing. There is currently no evidence that the Ronne Ice Shelf is calving more often as a result of climate change.'

According to Alex Brisbourne, a glaciologist at the British Antarctic Survey, who has worked on the Ronne Ice Shelf, 'Iceberg A76 is huge, about the size of the county of Somerset in the UK. It wouldn’t make the top 10 list of the biggest known icebergs of all time though. This calving is part of the natural cycle of the Ronne Ice Shelf. The ice shelf is constantly being fed ice from the Antarctic continent, and eventually chunks break off the ice shelf in this way, forming these big flat icebergs and maintaining a balance. Because they are already floating, as they melt, icebergs do not contribute to sea level rise in a significant way. They have been known to eventually get stuck in places like South Georgia in the South Atlantic, disrupting the feeding of Seals and Penguins.'

'We know that the ocean around Antarctica is warming as a result of global heating but the Weddell Sea, where iceberg A76 sits, is not currently experiencing this warming. Elsewhere around the Antarctic continent however, the warming ocean is melting other ice shelves and this is allowing the ice to drain more quickly off the continent, increasing the rate of sea level rise. Of course, this sea level rise isn’t restricted to Antarctica, it affects sea level around the world, including here in the UK, increasing the frequency and severity of storm surges and coastal flooding.'

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.

Large iceberg calves from the Brunt Ice Shelf, Antarctica.

A huge iceberg (1270 km² or the size of the county of Bedfordshire) has broken off the 150m thick Brunt Ice Shelf, according to a press release issued by the British Antarctic Survey on 26 February 2021, almost a decade after scientists first detected growth of vast cracks in the ice.

The Brunt Ice Shelf is the location of British Antarctic Survey’s Halley Research Station. British Antarctic Survey glaciologists, who have been expecting a big calving event for at least a decade, say that the research station is unlikely to be affected by the current calving.  The 12 person team working at the station left mid-February by British Antarctic Survey Twin Otter aircraft.  The station is now closed for the Antarctic winter.

 

North Rift crack photographed by Halley team in January 2021. British Antarctic Survey,

The first indication that a calving event was imminent came in November 2020 when a new chasm, called North Rift, headed towards another large chasm near the Stancomb-Wills Glacier Tongue 35 km away. North Rift is the third major crack through the ice shelf to become active in the last decade.

During January, this rift pushed northeast at up to 1 km per day, cutting through the 150 m thick floating ice shelf.  The iceberg was formed when the crack widened several hundred metres in a few hours on the morning of 26 February, releasing it from the rest of floating ice shelf.

 

Map of Brunt ice shelf and Halley Research Station. British Antarctic Survey.

The glaciological structure of this vast floating ice shelf is complex, and the impact of ‘calving’ events is unpredictable.  In 2016, the British Antarctic Survey took the precaution of relocating Halley Research Station 32 km inland to avoid the paths of ‘Chasm 1’ and ‘Halloween Crack’.

Since 2017, staff have been deployed to the station only during the Antarctic summer, because during the dark winter months evacuation would be difficult.  ‘Chasm 1’ and ‘Halloween Crack’ have not grown in the last 18 months.

Jane Francis, Director of the British Antarctic Survey said 'Our teams at the British Antarctic Survey have been prepared for the calving of an iceberg from Brunt Ice Shelf for years. We monitor the ice shelf daily using an automated network of high-precision GPS instruments that surround the station, these measure how the ice shelf is deforming and moving.  We also use satellite images from European Space Agency, NASA and the German satellite TerraSAR-X.  All the data are sent back to Cambridge for analysis, so we know what’s happening even in the Antarctic winter, when there are no staff on the station, it’s pitch black, and the temperature falls below minus 50 °C. Over coming weeks or months, the iceberg may move away; or it could run aground and remain close to Brunt Ice Shelf.  Halley Station is located inland of all the active chasms, on the part of the ice shelf that remains connected to the continent. Our network of GPS instruments will give us early warning if the calving of this iceberg causes changes in the ice around our station.'

Simon Garrod, Director of Operations at the British Antarctic Survey added 'This is a dynamic situation.  Four years ago we moved Halley Research Station inland to ensure that it would not be carried away when an iceberg eventually formed.  That was a wise decision.  Our job now is to keep a close eye on the situation and assess any potential impact of the present calving on the remaining ice shelf.  We continuously review our contingency plans to ensure the safety of our staff, protect our research station, and maintain the delivery of the science we undertake at Halley.'

Halley VI Research Station is an internationally important platform for, atmospheric and space weather observation in a climate-sensitive zone.  In 2013, the station attained the World Meteorological Organization Global Atmosphere Watch Global station status, becoming the 29th in the world and 3rd in Antarctica.  

Halley VI Research Station sits on Antarctica’s Brunt Ice Shelf, which is up to 150 m thick. This floating ice shelf flows at a rate of up to 2 km per year west towards the sea where, at irregular intervals, it calves off as icebergs.  

Long-term monitoring of the natural changes that occur in the ice shelf has revealed changes, including  growth of a recently-formed chasm, the North Rift. Halley VI Research Station has been unoccupied during the last four winters because of the complex and unpredictable glaciological situation. 

Change in the ice at Halley is a natural process and there is no connection to the calving events seen on Larsen C Ice Shelf, and no evidence that climate change has played a significant role.

During the 2016-17 Antarctic Summer season (Nov-March), in anticipation of calving, the eight station modules were uncoupled and transported by tractor to a safer location upstream of Chasm-1.

Over the summer 18/19, the British Antarctic Survey installed an autonomous power generation and management system, Halley Automation project, which provides a suite of scientific instruments with power even when we have no staff at the station. This system has proved effective in running through more than eight months of darkness, extreme cold, high winds and blowing snow and delivering important data back to UK.

There have been six Halley research stations on the Brunt Ice Shelf since 1956. 

See also...

 

 

 

 

 

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.

New crack spotted on the Brunt Ice Shelf, Antarctica.

In early 2019, all eyes were fixed on the Brunt Ice Shelf in Antarctica, where a massive iceberg, around the size of Greater London, appeared poised to break off. Almost two years later, the berg is desperately clinging on, although current data indicate calving is imminent. A new crack, spotted in images captured by the Copernicus Sentinel missions, now suggests the potential for calving of multiple bergs, according to a press release from the European Space Agency on 12 February 2021.

For years, glaciologists have been tracking a number of cracks in the Brunt Ice Shelf, which borders the Coats Land coast in the Weddell Sea sector of Antarctica. The lengthening of two main cracks in the ice shelf, separated only by a few kilometres, have been closely monitored by satellite imagery. Chasm 1, the large crack running northwards from the southernmost part of Brunt, has been set in place for more than 25 years, while the Halloween crack was first spotted on 31 October 2016.

A more recent, unnamed crack was first noticed in observations from the Copernicus Sentinel-1 mission in late-2019, recently extending by more than 20 km in length. Satellite data has also been used to track the movement and measure the resulting strain in the ice shelf. The map below shows the ice surface velocity on the Brunt and Stancomb-Wills Ice Shelf complex, derived by comparing two Sentinel-1 acquisitions captured on 5 January and 17 January 2021.

 

Ice velocity map of the Brunt and Stancomb-Wills Ice Shelf. European Space Agency.

The data indicate the region of the floating ice shelf, to the north of the new crack, to be the most unstable, with an approximate movement of almost 5 m per day. The central portion has an average velocity ranging from 2 to 2.5 m per day, while the lower area (visible in blue) suggests a more stable zone of the ice shelf.

'Though appearing poised to calve in 2019, the south westernmost region of the Brunt Ice Shelf tenaciously resisted separation,' noted European Space Agency’s Mark Drinkwater. 'Since then, Sentinel-1 data indicate the nose of the ice shelf to be pivoting clockwise around the McDonald Ice Rumples region in which point the shelf ice is grounded on shallow underwater topography.'

'Meanwhile, the strong gradient in ice velocity towards the faster moving Stancomb-Wills ice stream, and ice shelf in the north, has activated a new rift which now threatens the release of a second large iceberg.'

 

New crack in the Brunt Ice Shelf. European Space Agency.

Routine monitoring from satellites offer unprecedented views of events happening in remote regions, and show how ice shelves are responding to changes in ice dynamics, air and ocean temperatures. During the dark winter months in Antarctica, radar images are indispensable because, apart from the region being remote, radar continues to deliver images regardless of the dark weather.

Mark Drinkwater continued, 'With today’s Copernicus monitoring system, we are far better equipped not only to observe events in remote places like Antarctica in near real time, but more importantly, to turn this scientific data into theoretical understanding of complex ice fracture processes.'

History shows that the last major event took on the Brunt Ice Shelf took place in 1971, when a portion of ice calved north of the area known as the McDonald Ice Rumples in what appears to be replicated by today’s Halloween Crack.

With the ice shelf deemed unsafe due to the encroaching cracks in 2017, the British Antarctic Survey closed up their Halley VI Research Station, and re-positioned south of Halloween Crack to a more secure location. Operational since 2012, Halley VI is made up of eight interlinked pods built on skis. This allows the pods to be easily moved in case of unstable ice and cracks on the ice shelf.

 

Location of the Brunt Ice Shelf. European Space Agency.

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.

 

Greenland loses 12.5 billion tons of ice in a single day.

The Greenland Ice Sheet is calculated to have lost a total of 12.5 billion tons of water on Wednesday 31 July 2019, the highest ice loss ever recorded in Greenland in a single day; the last time a comparable loss was recorded was in 2012, when 10 billion tons was lost in a single day, something which was at the time thought to be a once in 250 year event at the time, and comes as part of a total calculated loss of about 197 billion tons of ice in the whole of July, roughly enough to raise global sea levels by about 0.5 mm.

A lake on top of floating ice in the Ilulissat Icefjord on 30 July 2019. Sean Gallup/Getty Images.

The Greenland Ice Sheet contains a total of about 2 850 000 cubic kilometres (about 2 850 000 gigatonnes) of ice, enough to raise global sealevels by about 7.2 m should it all melt. Sea level rise is only caused by the melting of ice on land, since sea-ice is already displacing water, nevertheless, should all the ice currently locked up in glaciers on land (most of which is in Antarctica) melt, then the sealevel would rise by about 70 m, which would have a severe impact on Human civilisation. 

Sea also...

Follow Sciency Thoughts on Facebook.

Evidence for a Carboniferous glaciation in the Ennedi-Bourkou Mountains of northern Chad.

During the Late Palaeozoic the supercontinent of Gondwana covered the Southern Polar Region, with the Pole itself moving across Africa and Australia. Evidence for an extensive Southern Polar Glaciation has been found in South Australia, Oman, Ethiopia, Brazil, Egypt, Niger, and Libya. The glaciation seen in Niger and Libya seems extremely likely to continue across the northern part of Chad, which separates the the two regions, however, the remote nature and political instability of this region has prevented exploration by geologists to date.

In a paper published in the journal Geology on 29 November 2017, Daniel Le Heron of the Department of Earth Sciences at Royal Holloway, University of London, describes the results of a study of the topography of the Ennedi-Bourkou Mountains of northern Chad, made using satellite data from Google Earth, which shows the presence of an extensive Carboniferous ice-stream system.

The Ennedi-Bourkou Mountains form the southern margin of the Al Kufrah Basin, which has striated surfaces interpreted as glacial in origin around Jabal Azbah on its eastern margin, in southern Libya. However no such structures have previously been described from the less well explored Chaddian portion of the basin. Le Heron found that the Ennedi-Bourkou Mountains show a series of sinuous belts cutting across a sandstone platform dated to the Carboniferous in the early 1960s (when nobody was looking for evidence of glaciation in the Central Sahara).

Lineament analysis of Google Earth imagery, Ennedi-Bourkou region, northern Chad, illustrating suite of curvilinear features interpreted as mega-scale glacial lineations traversing outcrop belts mapped as Devonian and Carboniferous. Sinuous belts of mega-scale glacial lineations are interpreted as paleo–ice stream pathways; neighbouring regions devoid of these are interpreted as inter-stream areas. The “Mousso” structure is a possible impact crater. Le Heron (2017).

Le Heron was able to detect five main sinuous belts, each 5-12 km in width, which, combined with the interstream areas, cover an area of about 6000 km². These belts can be traced for tens of kilometres, and run approximately north to south.

High-resolution view and interpretation of a paleo–ice stream track shown in Figure 2. Note deflection of mega-scale glacial lineations (MSGLs) around hill interpreted as a nunatak. Elevation of nunatak (1100 m) and of paleo–ice stream track to the west (850 m) allows maximum thickness of ice to be estimated (i.e. less than 250 m). La Heron (2017).<250 br="" m="">

The belts are cross-cut by more recent features, such as wadis and faults, supporting the interpretation of them as ancient structures, though it is impossible to tell whether they represent a single extended glacial event or a series of glacial cycles.

Series of snapshots from Google Earth imagery of the Ennedi-Bourkou plateaux (Chad) with accompanying interpretations. (A) Interaction of mega-scale glacial lineations (yellow lines) with dipping strata of presumed pre-glacial origin (orange lines), with interpreted glacial erosion surface indicated. Scale bar applies to immediate foreground only. (B) Low-angle perspective of interpreted palaeo–ice stream pathway shown in (A). Note interpreted inter-stream area which is devoid of mega-scale glacial lineations. (C) Mega-scale glacial lineations with evidence of fault offsets (faults in red), underscoring their antiquity (d—drumlins). (D) Development of mega-scale glacial lineations on two plateau levels. La Heron (2017).

The Chadian linear structures appear to cross cut layers of rock similar to those cross-cut by similar structures in Niger, which have been used to date the Niger structures to the Visean Stage, roughly 346.7 to 330.9 million years ago. This suggests an extensive Carboniferous ice sheet in the Sahara, draining to the north. This appears to correlate with an ancient palaeo-shoreline recorded in parts of northern Chad, and dated to about 350 million years ago. The absence of any known fluvial (river-generated) systems associated with this coastline suggests a significant ice-sheet covering the land and calving at the shore margin. 

Tentative paleogeographic reconstruction of Visean ice sheet in north-central Africa, incorporating ice flow directions in Aïr Massif of northern Niger with newly documented set of paleo–ice stream pathways in northern Chad. Speculated paleo–ice stream tracks are also shown. Coastline position for Tournasian at 350 Ma. Note close association of paleo–ice stream termini and palaeo-shoreline. La Heron (2017).

See also...

Follow Sciency Thoughts on Facebook.

Massive iceberg breaks away from Pine Island Glacier.

NASA's Aqua Satellite has recorded a massive iceberg breaking away from Pine Island Glacier, which flows along the south side of the Hudson Mountains into Pine Island Bay (named for the seaplane USS Pine Island which first explored the area, not for any local flora) drains about 10% of Antarctica's Western Ice Shelf. The iceberg, designated B-31, has an area of about 700 km², about the same size as Anglesey or Singapore, and broke away over the period 9-11 November 2013.

Images of Pine Island Glacier taken by Aqua on 3 November 2013 (top) and 10 November 2013 (bottom). Earth Observatory.

Pine Island Glacier has both accelerated and thinned notably since observations began, increasing in speed by about 73% and losing an average of 46 gigatonnes of mass per year between 1973 and 2007. The loss of icebergs from Pine Island Glacier into the sea is a natural process; all glaciers flow, and eventually either calve into the sea (or sometimes a big lake) or reach an area warm enough to melt, feeding streams and rivers. However the increase in the rate at which Pine Island Glacier is flowing and thinning is reason for concern. 

Glaciers are fed by precipitation, like rivers, but increased precipitation will not necessarily lead to increased flow as it will with a river, as the flow of a glacier is determined by its mass-balance ratio. Effectively this means a glacier's flow is driven by a combination of input and temperature. It the amount of precipitation increases and the temperature drops the glacier will slow and thicken. I the case of Pine Island Glacier it is thought that the increased flow is driven primarily by the warming of the Amundsen Sea, which removes more material at the calving front (warm a glacier and it calves more rapidly) causing the glacier to flow more rapidly, which in the absence of a notable increase in precipitation, has led the glacier to thin.

See also Huge iceberg calves from Pine Island Glacier, Huge iceberg breaks away from Peterman Glacier, Greenland, Possible volcanic activity on Mount Siple, Antarctica, Russian scientists prepare to break through into Lake Vostok and Drilling for Lake Ellsworth.

Follow Sciency Thoughts on Facebook.

Huge iceberg calves from Pine Island Glacier.

The DLR satellite TerraSAR-X observed a 720 km² iceberg calve away from the Pine Island Glacier in Antarctica and float free into the Amundsen Sea on Monday 8 July 2013. The glacier, which flows along the south side of the Hudson Mountains into Pine Island Bay (named for the seaplane USS Pine Island which first explored the area, not for any local flora) drains about 10% of Antarctica's Western Ice Shelf and has both accelerated and thinned notably since observations began, increasing in speed by about 73% and losing an average of 46 gigatonnes of mass per year between 1973 and 2007.

The newly formed iceberg (upper left) calving away from Pine Island Glacier. DLR.

The loss of icebergs from Pine Island Glacier into the sea is a natural process; all glaciers flow, and eventually either calve into the sea (or sometimes a big lake) or reach an area warm enough to melt, feeding streams and rivers. However the increase in the rate at which Pine Island Glacier is flowing and thinning is reason for concern. 

Glaciers are fed by precipitation, like rivers, but increased precipitation will not necessarily lead to increased flow as it will with a river, as the flow of a glacier is determined by its mass-balance ratio. Effectively this means a glacier's flow is driven by a combination of input and temperature. It the amount of precipitation increases and the temperature drops the glacier will slow and thicken. I the case of Pine Island Glacier it is thought that the increased flow is driven primarily by the warming of the Amundsen Sea, which removes more material at the calving front (warm a glacier and it calves more rapidly) causing the glacier to flow more rapidly, which in the absence of a notable increase in precipitation, has led the glacier to thin.

See also Hundreds feared dead after collapse of Chorabari Glacier,  Iceberg damage in an Antarctic Clam, Huge iceberg breaks away from Peterman Glacier, Greenland, Possible volcanic activity on Mount Siple, Antarctica and Russian scientists prepare to break through into Lake Vostok.

Follow Sciency Thoughts on Facebook.

Hundreds feared dead after collapse of Chorabari Glacier.

153 people are known to have died and thousands more are trapped after the Chorabari Glacier in Uttarkhand State, India, partially collapsed amid heavy rains associated with the onset of the Indian monsoon season. A wave of icy slush and mud described as two stories high hit the town of Kedarnath,  home of a Temple to the god Shiva, which is a popular pilgrimage site. The temple complex is said to be damaged but still standing, while much of the surrounding town has been destroyed. The Chorabari Glacier has retreated 326 m since records began in 1960, and may have been retreating since the mid eighteenth century. It is the source for the Mandakini River, a tributary of the Alaknanda River, and is itself an important site of Hindu pilgrimage.

Destruction in Kedarneth following the collapse of the Chorabari Glacier. STR/AFP.

The area has suffered extensive flooding with several rivers having burst their banks. At least 20 bridges and 365 houses have been destroyed, and hundreds of miles of roads have been washed away. In addition the area has suffered a large number of landslides, a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall, but the situation in Uttarkhand is thought to have been made much worse by extensive deforestation, sand extraction and quarrying (much of it illegal) and unregulated building construction across the affected area.

The Indian Government has begun a major rescue attempt in the area, where it is feared that thousands of trapped Hindu pilgrims from all over the world may become victims to disease and starvation. Lists of rescued pilgrims are being published on the websites http://uttarakhandpolice.uk.gov.in and www.uk.gov.in.

Buildings partially submerged by the swollen Alaknanda River in Govind Ghat, Uttarkhand State, India. AP.

A road partially destroyed by a landslide over a swollen river in Uttarkhand State. AFP/Getty Images.

The swollen River Ganges breaking over a statue of Shiva in Rishikesh, Uttarkhand State. State. AFP/Getty Images.

See also Three workers killed in landslide at Mumbai quarry, Seven killed in Nepal landslide, Three workers killed in rockfall at Thai limestone quarry, Fifteen-year-old boy killed in Kathmandu landslide and Huge iceberg breaks away from Peterman Glacier, Greenland.

Follow Sciency Thoughts on Facebook.

Huge iceberg breaks away from Peterman Glacier, Greenland.

On 16 July 2012 NASA's Aqua Satellite observed an iceberg measuring 120 km² (roughly 1.5 times the area of Manhattan Island or the Isle of Sheppey) the calving away from the Petermann Glacier in northern Greenland. This is not the largest iceberg ever seen calving away from Petermann, one twice this size was produced in 2010, but it is pretty large, and is part of an ongoing trend that has seen the size of the glacier greatly diminished. 

False-colour satellite image of the new iceberg. Washington Post/University of Delaware.

The Petermann Glacier is a 70 × 15 km³ floating ice tongue connecting the Greenland Ice-sheet to the Arctic Ocean, along the Petermann Fjord. Like all glaciers it ebbs and flows over time. The 2010 calving event reduced the glacier's area by about 25%, and the 2012 event shrinks it to its smallest for 150 years.

The location of the Petermann Glacier. BBC/NASA.

The exact relationship between glacial calving and global temperatures in complicated, and glaciologists are (rightly) reluctant to relate any particular event to global warming. A glacier shrinking to its smallest for 150 years is not evidence that the climate has changed notably from 150 years ago, particularly as the growth and shrinkage of glaciers appears to be a cyclical event. However if the overwhelming majority of the worlds glaciers appear to be retreating at the same time, as is currently the case, then this is cause for alarm.

Melting ice in the Arctic is often linked to global sea-level rise, however this only applies to the melting of ice on-land, such as the Greenland Ice-sheet. The melting of floating glaciers such as Petermann has no effect on sea-levels, as the floating sea-ice displaces an equivalent amount of water to that produced when it melts.

See also Bowhead Whales in the Northwest Passage, Greenpeace activists occupy drilling ship in New Zealand, Were a string of volcanic eruptions responsible for the Little Ice Age? Industrialization of the East Canadian Tundra blamed for 90% drop in Caribou numbers and Greenpeace activists occupy the offices of Cairn Energy in protest at Greenland drilling.

Follow Sciency Thoughts on Facebook.