Sciency Thoughts: Holland

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Tuesday, 12 September 2017

Hurricane Irma kills forty two in the Caribbean, causes widespread flooding in Florida.

Forty two people have now been confirmed dead in incidents relating to Hurricane Irma in the Caribbean. Eleven people have died in the French colonies of Saint Martin and Saint Barthélemy, ten on the island of Cuba, five in the state of Florida, four each on the Dutch colony of Sint Maartin and the US Virgin Islands, three each in Peurto Rico and Barbuda, and one each in Anguila and Barbados. The hurricane was a Catagory Five tropical storm when it hit the Leeward Islands, with sustained winds in excess of 250 km per hour and gusts considerably stronger. By the time it hit Florida it had dropped to Catagory Four storm,with winds in excess of 210 km per hour and larger gusts. However the majority of the damage has been done by storm surges, with waves in excess of five meters recorded on the Florida Keys, and in excess of three meters on the mainland.

Flooding in Havana, Florida, on 10 September 2017 following the passage of Hurricane Irma. Yamil Lage/AFP/Getty Images.

Hurricane Irma swept across Barbuda om 5-6 September, destroying 95% of the buildings on the island, including its only hosptital. Despite this only a single fatality has been reported on the island, with two more people missing and three more injured. The storm hit the island of Saint Martin, which is divided between the French colony of Saint Martin and the Dutch colony of Sint Maartin, the following morning, killing eleven people and injuring 40 more on the French part of the island, where about 90% of the buildings have been damaged and about 60% are unihabitable, and killing four and injuring 23 on the Dutch part, where about 70% of the buildings have been damaged.

Storm damage on Sint Maartin following the passage of Hurricane Irma. Gerban Van Es/Zuma Press.

The storm hit the British colony of Antigua later the same day, agian causing widespread damage and killing one person, though rmost of the island's buildings are relatively intact. The islands of Saint Lucia, Barbados, Guadeloupe, St Kitts, Nevis, Saba and Sint Eustatius were missed by the main hurricane, but were hit by storm surges, with one person killed on Barbados. The storm next swept across the Virgin Islands, passing directly over Tortola and Necker islands the British part of the group, where it caused extensive damage. The US islands of Saint Thomas, Saint Croix and Saint John were hit by storm surges, causing widespread damage and killing four people.

Damage in Road Town on the island of Tortola, in the British Virgin Islands, following the passage of Huricane Irma. Joel Rouse/MoD/PA.

The islands of Puerto Rico and Hispaniola were missed by the storm but hit by severe storm surges, with waves i excess of nine meters recorded on Puerto Rico. Both islands suffered severe damage, with three known casualties on Puerto Rico. The storn passed across Ambergis Cays in the Turks and Caicos Islands on the evening of 7 September, causing extensive damage throughout the island group, but no casualties. On the morning of 8 September it hit the Bahamas, passing directly over the Ragged Islands, Inagua and South Atkins, again causing widespread damage but no known casualties.

Flooding on Peurto Rico following the passage of Hurricane Irma. David Goldman/AP.

The hurricane made landfall in Cuba late on 8 September, brining with it winds in excess of 260 km per hour and waves over five meters high. The storm killed at least ten people on the island, with extensive damage to the towns of Caibarién, Havana and Santa Clara.

Flooding in Havana on 10 September 2017. Yamil Lage/AFP/Getty Images.

The storm hit Cudjoe Key, Florida at 9.10 am on 10 September, brining with it waves in excess of three meters. It hit the city of Marco Island, on the Florida mainland at 3.35 pm on the same day, brining winds in excess of 175 km per hour and causing widespread flooding across much of the state. Five people have died in Florida, a number probably much lower than it could have been due to the evacuation of around 6.5 million people from areas in the path of the storm.

Flooding in Miami during the passage of Hurricane Irma. Carlos Barria/Reuters.

Tropical storms are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm. They have different names in different parts of the world, with those in the northwest Atlantic being referred to as hurricanes.

The path and strength of Hurricane Irma. Thick line indicates the past path of the storm (till 9.00 pm GMT on Monday 11 September 2017), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at six and twelve hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

Thursday, 7 September 2017

Hurricane Irma leaves widespread devastation across the Caribbean and causes at least ten deaths.

Ten people have now been confirmed dead on Caribbean islands hit by Hurricane Irma this week, with it likely that many more deaths are yet to be reported due to the extensive damage the storm has caused. Eight people are known to have died on the French half of the Island of St Martin, where the storm is reported to have levelled 95 % of all buildings. On the island of Barbuda about 90% of buildings have been flattened and a two-year-old child has been reported dead, while one death has been confirmed on the British island of Anguilla.

Damage left by Hurricane Irma on the Dutch part of the island of St Martin. Gerben Van Es/AFP/Getty Images.

Hurricane Irma was a Category 5 storm when it passed over the islands, with sustained winds in excess of 250 km per hour and gusts considerably stronger. After passing over Barbuda, St Martin and Anguilla the storm swept across the British and US Virgin Islands, where it is likely to have caused further, as yet unreported, fatalities, then to the north of Peurto Rico, the Dominican Republic and Haiti, and is currently heading towards the Bahamas and Florida, where authorities have organised mass evacuations.

The path and strength of Hurricane Irma. Thick line indicates the past path of the storm (till 3.00 pm GMT on Thursday 7 September 2017), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at six and twelve hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.

Damage caused by Hurricane Irma on the French part of the island of St Martin. Rinsy Xing/AFP/Getty Images.

Sunday, 28 August 2016

Analysing the distribution of Pleistocene Terrestrial Vertebrate Fossils from the North Sea.

Today the UK is an island separated from the European mainland by the North Sea and English Channel, but for much of the Pleistocene the UK was attached to the rest of Europe, with large areas of land that were occupied by early Humans and other terrestrial animals. Over the past two centuries a very large number of Pleistocene Terrestrial Vertebrate Fossils have been recovered from the North Sea. Some of this has some from sites which have been the site of organised archaeological and palaeontological investigations, such as Bouldnor Cliff in the Solent (not strictly part of the North Sea), Area 240 off the north coast of Norfolk and Brown Bank and Eurogeul off the coast of the Netherlands, but the largest proportion of the material has been brought up by fishing trawlers and dredgers from areas never directly accessed by archaeologists or palaeontologists. In recent years some effort has been made to analyse North Sea material in Dutch collections in order to build up a picture of the age of the specimens, and understand the environments in which they were living.

In a paper published in the journal Antiquity on 28 June 2016, Rachel Bynoe of the Department of Archaeology at the University of Southampton, Justin Dix of the National Oceanography Centre Southampton, also at the University of Southampton, and Fraser Sturt, again of the Department of Archaeology at the University of Southampton describe the results of a study of 1120 specimens collected from the North Sea and currently in the collections of museums in the east of England.

Bynoe et al. identified three main areas targeted by large fishing fleets from the East of England in the nineteenth and twentieth centuries. The area from the Dogger Bank, northward to the Skagerrak and towards the Shetland Islands, Greenland and the Barents Sea was targeted by fleets from the ports of Grimsby and Hull, the area from Dogger Bank south to the Leman and Ower Banks was exploited by the Yarmouth Fleet and the area south of the Leman and Ower Banks, east to the Dutch coast and south to the Gabbards was utilised by the fleet from Lowestoft. In addition numerous smaller coastal fleets targeted inshore areas close to their home ports.

All locations and sites mentioned in the text, with contours showing current offshore bathymetry. Bynoe et al. (2016).

The accessible fossil record of the North Sea is known to be skewed; only the largest and most robust specimens are likely to have survived on the sea floor for thousands of years, become entangled in fishing nets then spotted by Human observers not specifically looking for fossil remains. Nevertheless even with such a bias towards large specimens some biostratigraphical and environmental reconstruction is possible; in particular considerable faunal turnover is associated with the Anglian Glaciation (roughly 478 000–424 000 years ago), when the glaciers reached as far south as London, and most specimens can be confidently described as belonging to pre- or post-Anglian Glaciation species. Likewise some species present were clearly not adapted to colder conditions (such as the Straight-tusked Elephant, Palaeoloxodon antiquus, or Narrow-nosed Rhinoceros, Stephanorhinus hemitoechus) and therefore must have lived during warm, interglacial periods.

Of the examined specimens 71% were found to have sufficient information to tie them to an approximate location. The information recorded at the time when the fossils were collected is often somewhat vague, such as 'East Coast' or 'Suffolk'; however this can be further refines, for example a specimen labelled 'Suffolk' is likely to have been collected by a fishing vessel from Lowestoft, and therefore can be assigned to the area targeted by the Lowestoft fleet. The identity of the collectors that amassed the material and donated it to the museums was also useful, for example the antiquarian John Owles is known to have collected material brought ashore by the Great Yarmouth fleet in the mid nineteenth century, so fossils collected by him and labelled 'East Coast' can be assigned to the area targeted by the Great Yarmouth fleet.

Cervus sp. skull showing Owles’s Great Yarmouth stamp. Bynoe et al. (2016).

Of the Great Yarmouth specimens 85% are considered to be post-Anglian species, with 9% pre-Anglican and 6% species present both before and after the Anglian glaciation. 68% of the post-Anglian specimens are assigned to a single species, the Woolly Mammoth, Mammuthus primigenius, with the Woolly Rhinoceros, Coelodonta antiquitatis, and the Aurochs, Bos primigenius, each making up 6% of the specimens, Reindeer, Rangifer tarandus, made up 3% of these specimens, and Walrus, Trichechus rosmarus, and Giant Deer, Megaloceros giganteus, each making up less than one percent of the specimens. The warm-climate Straight-tusked Elephant, Palaeoloxodon antiquus, was also present, albeit at a very low level.

Post-Anglian species also dominated the Lowestoft specimens, comprising 72% of the total, though here pre-Anglican specimens made up 19% of the total and species present both before and after the Anglian glaciation made up 9% of the total. Again the most abundant species in the post-Anglican set was the Woolly Mammoth, Mammuthus primigenius, though here it only made up 51% of the total, with the Aurochs, Bos primigenius, making up 9% of the specimens, and the Woolly Rhinoceros, Coelodonta antiquitatis, making up 8%.

The inshore specimens shore a more detailed picture, with the northern coast of East Anglia having an assemblage dominated by pre-Anglian specimens, with the proportion of post-Anglian specimens rising further south along the coast, with a distinct pocket of warm-climate species including Straight-tusked Elephant, Palaeoloxodon antiquus, or Narrow-nosed Rhinoceros, Stephanorhinus hemitoechus and Hippopotamus sp. found around the Tendring Peninsula, interpreted as having been deposited late in the last interglacial period; a hypothesis supported by a sediment core taken from nearby deposits that yielded an optically stimulated luminescence date of about 116 000 years ago.

(a) Changing proportions along the coastal locations; (b) changing proportions from Great Yarmouth and Lowestoft fleets, plus inset chart showing the coastal species from locations with larger sample sizes. Bynoe et al. (2016).

This data ties in well from that from the Dutch coastal sites, which are likely to overlap with the Lowestoft data, which yielded radiocarbon dates of 60 000–15 000 years ago and an environmental reconstruction that suggests the area was dominated be Mammoth Steppe; a cold grassland environment most associated with the last glaciation, appearing slightly over 100 000 years ago and disappearing about 12 000 years ago. These Dutch deposits have also produced the only known Pleistocene Human remains from the North Sea, a Neanderthal brow ridge from the Zeeland Ridges.

Thursday, 10 January 2013

Earthquake off the coast of Holland.

On Saturday 5 January 2013, at 11.15 pm GMT, the British Geological Survey recorded a Magnitude 2.7 Earthquake at a depth of 5 km, roughly 20 km off the coast of Den Helder, Holland. This is too small and too far offshore to present a risk of damage or injuries, and may not have been noticed at all.

The location of the 5 January Earthquake. Google Maps.

The Netherlands is not a country always associated with Earthquakes, but it is bounded to the south by the Lower Rhine Graben, an area of tectonic expansion beneath the Rhine Valley, and to the north by the North Sea Central Graben, the Terschelling Graben and The Horn Graben, two similar areas of expansion beneath the North Sea. These areas do not generate new ocean floor or expand on the same scale as the Mid Atlantic Ridge or similar structures, but they do exert pressure on the rocks around the North Sea Basin, and can lead to Earthquakes in any of the countries surrounding the Basin.

Map showing the location of the North Sea Central and Terschelling Grabens. Numbered locations are oil rigs. Abbink et al. (2001).

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