Shag Rock is a small rocky island in the

Wallabi Group The Wallabi Group is the northernmost group of islands in the Houtman Abrolhos off the western coast of Western Australia. it is from the Australian mainland, and about from the Easter Group. The group consists of a numbe ...

of the

Houtman Abrolhos The Houtman Abrolhos (often called the Abrolhos Islands) is a chain of 122 islands and associated coral reefs, in the Indian Ocean off the west coast of Australia, about west of Geraldton, Western Australia. It is the southernmost true coral ...

Geography

It is located at ,

Gazetteer of Australia The Gazetteer of Australia is an index or dictionary of the location and spelling of geographical names across Australia. Geographic names include towns, suburbs and roads, plus geographical features such as hills, rivers, and lakes. The index is ...

(1996). Belconnen, ACT: Australian Surveying and Land Information Group. about east of

West Wallabi Island West Wallabi Island is an island in the Wallabi Group of the Houtman Abrolhos, in the Indian Ocean off the west coast of mainland Australia. History West Wallabi Island was important in the story of the ''Batavia'' shipwreck and massacre. Foll ...

.Australia 1:100000 Topographic Survey, Map sheet 1641 (Edition 1): Wallabi Its nearest neighbour is Plover Island, about away. The island has an area of about , and a maximum elevation of . It is uninhabited, and devoid of human infrastructure. This island should not be confused with the rocky island that lies to the west of

North Island The North Island, also officially named Te Ika-a-Māui, is one of the two main islands of New Zealand, separated from the larger but much less populous South Island by the Cook Strait. The island's area is , making it the world's 14th-largest ...

. The latter has no gazetted name, but is informally known as "Shag Rock".

Geology and physiography

Shag Rock is essentially an outcrop of

Wallabi Limestone Wallabi Limestone is the name given to the dense calcretised, limestone platform that underlies the Wallabi Group of the Houtman Abrolhos, an archipelago off the coast of Western Australia. This platform, which arises abruptly from a flat shelf, i ...

, a dense calcretised,

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

platform that underlies the entire Wallabi Group. This platform, which arises abruptly from a flat shelf, is about thick, and is of

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

origin. Reef that formed during the

Eemian Stage The Eemian (also called the last interglacial, Sangamonian Stage, Ipswichian, Mikulin, Kaydaky, penultimate,NOAA - Penultimate Interglacial Period http://www.ncdc.noaa.gov/global-warming/penultimate-interglacial-period Valdivia or Riss-Würm) wa ...

(about 125,000 years ago), when sea levels were higher than at present, are now emergent in places, and constitute the basement of the group's "central platform" islands, of which Shag Island is one.

Flora

About half of the island, including most of its centre, is rock with no vegetation cover. A very small area just south of the centre is vegetated by ''

Tecticornia halocnemoides ''Tecticornia halocnemoides'', commonly known as shrubby samphire or grey glasswort,* is a species of succulent plant, succulent, halophyte, salt tolerant plant endemic to Australia. It grows as a spreading or erect shrub up to fifty centimetre ...

'' (Shrubby Samphire). The remainder of the island, predominantly the northern third and a patch in the south west, is vegetated by ''

Atriplex cinerea ''Atriplex cinerea'', commonly known as grey saltbush, coast saltbush, barilla or ''truganini'', is a plant species in the family Amaranthaceae. It occurs in sheltered coastal areas and around salt lakes in the Australian states of Western Aust ...

'' (Grey Saltbush), ''

Nitraria billardierei ''Nitraria billardierei'', commonly known as nitre bush or dillon bush, is a perennial shrub native to Australia. It is often found in saline areas or other areas which have been disturbed. This species produces flowers predominantly in spring, ...

'' (Nitre Bush) and ''

Pittosporum phillyreoides ''Pittosporum phillyreoides'', with the common names weeping pittosporum and willow pittosporum, is a shrub or small columnar tree in the Apiales order, endemic to Australia. Taxonomy This species is subject to some taxonomic confusion. It was ...

'' (Weeping Pittosporum). Data also available in

References

{{reflist Wallabi Group Uninhabited islands of Australia