The Lord Howe Rise is a

deep sea The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of or the point of transition from continental shelves to continental slopes. Conditions within the deep sea are a combination of low tempe ...

plateau In geology and physical geography, a plateau (; ; : plateaus or plateaux), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. ...

which extends from south west of

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

to the Challenger Plateau, west of

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

in the south west of the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

. To its west is the Tasman Abyssal Plain and to the east is the New Caledonia Basin. Lord Howe Rise has a total area of about , and generally lies about 750 to 1,200 metres under water. It is part of

Zealandia Zealandia (pronounced ), also known as (Māori language, Māori) or Tasmantis (from Tasman Sea), is an almost entirely submerged continent, submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83� ...

, a much larger

continent A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...

that is now mostly submerged, and so is composed of

continental crust Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as '' continental shelves''. This layer is sometimes called '' si ...

. Some have included the deep New Caledonia Basin as within the rise, given its continental crust origin, and this would give a larger total area of .

Geology

The Lord Howe Rise is associated with

seafloor spreading Seafloor spreading, or seafloor spread, is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. History of study Earlier theories by Alfred Wegener ...

which also resulted in the creation of the Tasman Sea. The geology has not yet been characterised as well as other parts of Zealandia but when previous samples are analysed with current geological techniques they fit with the Zealandia hypothesis. The seafloor is known to be dominated by soft sediments and the highest quality recent survey only mapped approximately of the western flank of the rise which is less than 1% of the total area of the rise. In this area about 0.1% of the rises seafloor was classed as hard substrata based on a combined area of for 16 volcanic peaks. Sandstone rocks dredged from the central Lord Howe Rise contained

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

pebbles that were in the range 216–183 million years old. It was

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...

ed away from

Eastern Australia The eastern states of Australia are the states adjoining the east continental coastline of Australia. These are the mainland states of Victoria, New South Wales and Queensland, and the island state of Tasmania. The Australian Capital Territor ...

in association with a

mid-ocean ridge A mid-ocean ridge (MOR) is a undersea mountain range, seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading ...

that was active from 80 to 60 million years ago, and now lies 800 kilometres offshore from

mainland Australia Mainland Australia is the main landmass of the Australia (continent), Australian continent, excluding the Aru Islands Regency, Aru Islands, New Guinea, Tasmania, and other list of islands of Australia, Australian offshore islands. The landmass ...

. The Lord Howe Rise contains a line of

seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...

s called the Lord Howe Seamount Chain which formed during the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

period when this part of Zealandia existed over the Lord Howe hotspot. One

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

sample has been dated at 97 million years drilled on the southern Lord Howe Rise.

Lord Howe Island Lord Howe Island (; formerly Lord Howe's Island) is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, part of the Australian state of New South Wales. It lies directly east of mainland Port ...

was the last volcano to erupt on the rise 6.5 million years ago.

Islands, reefs and seamounts

and

Ball's Pyramid Ball's Pyramid is an uninhabited islet in the Pacific Ocean located southeast of Lord Howe Island, between Australia and New Zealand. The steep rocky basalt outcrop is the eroded plug of a shield volcano and caldera that formed 6.4million ye ...

cap a seamount towards the central east of the rise in an area known as the Lord Howe platform. The Lord Howe Seamount Chain extends northwards along the rise. The seamounts provide habitat to a diverse range of marine species which attracts commercial fishers, but cover a very small area, less than 1% of the total area of Lord Howe Rise. Further north is the Elizabeth and Middleton part of the

Coral Sea Islands The Coral Sea Islands Territory is an States and territories of Australia#External territories, external territory of Australia which comprises a group of small and mostly uninhabited tropical islands and reefs in the Coral Sea, north-east of ...

, which together with reefs around

are the most southern coral reefs on Earth.

Environment

The

seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

on the rise is mostly sandy mud with some volcanic outcrops, gravel and boulders. The doubleheader fish, '' Coris bulbifrons'', is endemic to reefs on the Lord Howe Rise and the West Norfolk Rise.

Resources

Much of the basin remains unexplored in relation to oil and gas reserves.

References

{{Oceanic features of Zealandia, state=collapsed Plateaus of Oceania Underwater ridges of the Pacific Ocean Zealandia Tasman Sea

Geology

Islands, reefs and seamounts

Environment

Resources

See also

References