Helen's Reef is a series of

skerries A skerry is a small rocky island, usually defined to be too small for habitation. Skerry, skerries, or The Skerries may also refer to: Geography Northern Ireland *Skerries, County Armagh, a List of townlands in County Armagh#S, townland in Coun ...

in the

North Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...

, northeast of the larger

islet An islet ( ) is generally a small island. Definitions vary, and are not precise, but some suggest that an islet is a very small, often unnamed, island with little or no vegetation to support human habitation. It may be made of rock, sand and/ ...

Rockall Rockall () is a high, uninhabitable granite islet in the North Atlantic Ocean. It is west of Soay, St Kilda, Scotland; northwest of Tory Island, Ireland; and south of Iceland. The nearest permanently inhabited place is North Uist, east in ...

and outcrop of

Hasselwood Rock Hasselwood Rock is a skerry 200 metres North of Rockall in the North Atlantic. Location and characteristics Hasselwood Rock is some north of the larger outcrop of Rockall.G. S. Holland and R. A.GardinerThe First Map of Rockall. The Geographica ...

, within the United Kingdom's

exclusive economic zone An exclusive economic zone (EEZ), as prescribed by the 1982 United Nations Convention on the Law of the Sea, is an area of the sea in which a sovereign state has exclusive rights regarding the exploration and use of marine natural resource, reso ...

. The skerries are covered at high tide or in rough seas, and are often only visible as breaking waves. It is within the territorial waters of Rockall, which is claimed by the UK as of 1955 and incorporated into the UK by the

Island of Rockall Act 1972 The Island of Rockall Act 1972 (c. 2) is a British act of Parliament formally incorporating the island of Rockall into the United Kingdom to protect it from Irish and Icelandic claims. The act as originally passed declared that the Island of R ...

. This claim was previously long disputed by Ireland, but the dispute is resolved as of 31 March 2014.

History

Helen's Reef was named after the

brigantine A brigantine is a two-masted sailing vessel with a fully square-rigged foremast and at least two sails on the main mast: a square topsail and a gaff sail mainsail (behind the mast). The main mast is the second and taller of the two masts. Ol ...

''Helen'' of

Dundee Dundee (; ; or , ) is the List of towns and cities in Scotland by population, fourth-largest city in Scotland. The mid-year population estimate for the locality was . It lies within the eastern central Lowlands on the north bank of the Firt ...

, bound for

Quebec Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...

, which foundered at Hasselwood Rock in 1824. The vessel struck between nine and ten o'clock on the morning of 17 April. After some twelve hours struggling to keep her afloat and make for safety, water had almost filled the hold. The captain ordered the passengers onto the deck with warm clothing. Difficulty was experienced launching the boats, and one had to be repaired after being holed on the stock of the kedge anchor; On 28 June 1904 the 3,318-ton

DFDS DFDS is a Danish international shipping and logistics company. The company's name is an abbreviation of Det Forenede Dampskibs-Selskab (literally ''The United Steamship Company''). DFDS was founded in 1866, when Carl Frederik Tietgen, C.F. Tiet ...

steamer , with 795 people including 240 children on board bound for

New York New York most commonly refers to: * New York (state), a state in the northeastern United States * New York City, the most populous city in the United States, located in the state of New York New York may also refer to: Places United Kingdom * ...

, foundered on the reef. 635 lives were lost with most of the 163 survivors being taken to

Stornoway Stornoway (; ) is the main town, and by far the largest, of the Outer Hebrides (or Western Isles), and the capital of Lewis and Harris in Scotland. The town's population is around 6,953, making it the third-largest island town in Scotlan ...

. The wreck was found a century later in of water.

Geology

Helen's Reef is the tip of a narrow curvilinear

shoal In oceanography, geomorphology, and Earth science, geoscience, a shoal is a natural submerged ridge, bank (geography), bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body ...

rising from depth, located approximately east of Rockall Island. The reef coincides with a large negative

magnetic anomaly In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

encircling Rockall Island. Echo-sounder traverses and observations by divers have shown that the reef forms a narrow

pinnacle A pinnacle is an architectural element originally forming the cap or crown of a buttress or small turret, but afterwards used on parapets at the corners of towers and in many other situations. The pinnacle looks like a small spire. It was main ...

that breaches the surface and rises from a plateau at depth. That plateau comprises spurs and

buttress A buttress is an architectural structure built against or projecting from a wall which serves to support or reinforce the wall. Buttresses are fairly common on more ancient (typically Gothic) buildings, as a means of providing support to act ...

es with steep or vertical, joint-controlled or columnar-jointed faces descending to and depth. The south-eastern face is similarly steep and joint controlled, as on Rockall Island. Both Rockall and Helen's Reef may represent resistant stacks formed during a period of lower sea level.

Composition

Rock samples obtained by divers in the 1970s show that Helen's Reef is predominantly composed of

microgabbro Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained ...

with an equigranular (2–3 mm), holocrystalline, subophitic texture. These dark grey samples bear very light grey speckles in the coarser-grained facies. Mineral constituents include unaltered, colourless

forsterite Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich Endmember, end-member of the olivine solid solution series. It is Isomorphism (crystallography), isomorphous with the iron-rich end-member, fayalit ...

, pale green to pale brown

pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...

(endiopside) and

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

(

bytownite Bytownite is a calcium rich member of the plagioclase solid solution series of feldspar minerals with composition between anorthite and labradorite. It is usually defined as having between 70 and 90% An (formula: ). Like others of the series, byt ...

) laths. Chromian

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

occurs as dispersed cubes and octahedra; although it is a minor phase, its high

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

content (up to 13.5 % Cr₂O₃) may account for the prominent

. In the southern reef, a finer-grained, microporphyritic

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grain ...

—a rock with small olivine crystals set in a fine-grained matrix—forms a sharp chilled contact against the microgabbro. In the northern reef, local

cumulates Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group ...

and

with subordinate

indicate that heavier crystals sank under gravity as the magma cooled. These layered cumulate textures hint at further stratification in the unexplored deeper base of the reef. Chemical analyses indicate that Helen's Reef rocks differ markedly from

tholeiites The tholeiitic magma series () is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic ...

s of the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a Divergent boundary, divergent or constructive Plate tectonics, plate boundary) located along the floor of the Atlantic Ocean, and part of the List of longest mountain chains on Earth, longest mountai ...

but resemble Tertiary gabbroic intrusions, especially olivine-gabbro sills on

Skye The Isle of Skye, or simply Skye, is the largest and northernmost of the major islands in the Inner Hebrides of Scotland. The island's peninsulas radiate from a mountainous hub dominated by the Cuillin, the rocky slopes of which provide some o ...

that belong to the Porphyritic Central Magma Series of

Mull Mull may refer to: Places *Isle of Mull, a Scottish island in the Inner Hebrides ** Sound of Mull, between the Isle of Mull and the rest of Scotland * Mount Mull, Antarctica * Mull Hill, Isle of Man * Mull, Arkansas, a place along Arkansas Highwa ...

and

Ardnamurchan Ardnamurchan (, ) is a peninsula in the ward management area of Lochaber, Highland, Scotland, noted for being very unspoiled and undisturbed. Its remoteness is accentuated by the main access route being a single track road for much of its l ...

Age and significance

Potassium–argon dating of the microgabbro samples yielded a

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

age of 81 ± 3 Ma, which predates the 52 ± 9 Ma

aegirine Aegirine is a member of the clinopyroxene group of inosilicate minerals. It is the sodium endmember of the aegirine– augite series. It has the chemical formula NaFeSi2O6, in which the iron is present as the ion Fe3+. In the aegirine–augite se ...

granite of Rockall Island and reveals an earlier, previously unsuspected phase of igneous activity in the region. The Cretaceous

magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...

at Helen's Reef may relate to one of two spreading events that isolated the

Rockall Plateau The Rockall Trough () is a deep-water bathymetric feature to the northwest of Scotland and Ireland, running roughly from southwest to northeast, flanked on the north by the Rockall Plateau and to the south by the Porcupine Seabight. At the ...

microcontinent: the opening of the

Rockall Trough The Rockall Trough () is a deep-water bathymetric feature to the northwest of Scotland and Ireland, running roughly from southwest to northeast, flanked on the north by the Rockall Plateau and to the south by the Porcupine Seabight. At the n ...

in the Middle–Early Cretaceous or the opening of the

Labrador Sea The Labrador Sea (; ) is an arm of the North Atlantic Ocean between the Labrador Peninsula and Greenland. The sea is flanked by continental shelf, continental shelves to the southwest, northwest, and northeast. It connects to the north with Baffi ...

beginning around 80 Ma. The positioning of the microgabbros along the western margin of the Rockall Trough favours their

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

during the trough's formation. This activity may be linked to the early opening of the

North Atlantic Ocean The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

, including the contemporaneous formation of the Rockall Trough and the

Bay of Biscay The Bay of Biscay ( ) is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Point Penmarc'h to the Spanish border, and along the northern coast of Spain, extending westward ...

References

{{Reflist, refs= Written Answers - Rockall Island
{{Webarchive, url=https://web.archive.org/web/20140312000924/http://debates.oireachtas.ie/dail/2011/03/24/00043.asp , date=12 March 2014 . ''debates.oireachtas.ie'' 24 March 2011. Retrieved 6 April 2014.
''www.irishstatutebook.ie.'' Retrieved 20 July 2014. Clive Symmons "Ireland and the Rockall Dispute: An Analysis of Recent Developments" Durham University
''www.dur.ac.uk'' {{cite web , last=Follett , first=Christopher , title=Watch out for the big rock: Remembering Denmark's greatest maritime disaster , url=https://cphpost.dk/?p=74931 , publisher=Copenhagen Post , access-date=25 January 2022 , date=28 November 2016 "The Exclusive Economic Zone Order 2013"
''www.legislation.gov.uk'' Retrieved 20 July 2014. {{cite journal , last1=Roberts , first1=D.G. , last2=Flemming , first2=N.C. , last3=Harrison , first3=R.K. , last4=Binns , first4=P.E. , last5=Snelling , first5=N.J. , title=Helen's Reef: a microgabbroic intrusion in the Rockall intrusive centre, Rockall Bank , journal=Marine Geology , volume=16 , issue=1 , year=1974 , doi=10.1016/0025-3227(74)90021-8 , pages=M21–M30 , url=https://www.researchgate.net/publication/229164610 Rockall Reefs of the Atlantic Ocean Skerries of Scotland Landforms of the Outer Hebrides Reefs of Scotland