Underwater environment in the context of "Underwater vehicle"

A submerged continent or a sunken continent is a region of continental crust, extensive in size but mainly undersea. The terminology is used by some paleogeologists and geographers in reference to some landmasses (none of which are as large as any of the seven generally-recognized continents).

The definition of this term is unclear. If continental fragments and microcontinents smaller than 2,500,000 km (970,000 sq mi), which is approximately one third of the area of mainland Australia, are excluded, then Zealandia (approximately 4,900,000 km or 1,900,000 sq mi) would be the only geological feature which is classifiable as a submerged continent.

A diving mask (also half mask, free-diving mask, snorkelling mask or scuba mask) is an item of diving equipment that allows underwater divers, including scuba divers, underwater hockey players, underwater rugby players, free-divers, and snorkellers to clearly see underwater. Surface supplied divers usually use a full face mask or diving helmet, but in some systems the half mask may be used. When the human eye is in direct contact with water as opposed to air, its normal environment, light entering the eye is refracted by a different angle and the eye is unable to focus the light on the retina. By providing an air space in front of the eyes, the eye is able to focus nearly normally. The shape of the air space in the mask slightly affects the ability to focus. Corrective lenses can be fitted to the inside surface of the viewport or contact lenses may be worn inside the mask to allow normal vision for people with focusing defects.

When the diver descends, the ambient pressure rises, and it becomes necessary to equalise the pressure inside the mask with the external ambient pressure to avoid the barotrauma known as mask squeeze. This is done by allowing sufficient air to flow out through the nose into the mask to relieve the pressure difference, which requires the nose to be included in the airspace of the mask. Equalisation during ascent is automatic as excess air inside the mask easily leaks out past the seal.

Undersea mountain ranges are mountain ranges that are mostly or entirely underwater, and specifically under the surface of an ocean. If originated from current tectonic forces, they are often referred to as a mid-ocean ridge. In contrast, if formed by past above-water volcanism, they are known as a seamount chain. The largest and best known undersea mountain range is a mid-ocean ridge, the Mid-Atlantic Ridge. It has been observed that, "similar to those on land, the undersea mountain ranges are the loci of frequent volcanic and earthquake activity".

In zoology, deep-sea gigantism or abyssal gigantism is the tendency for species of deep-sea dwelling animals to be larger than their shallower-water relatives across a large taxonomic range. Proposed explanations for this type of gigantism include necessary adaptation to colder temperature, food scarcity, reduced predation pressure and increased dissolved oxygen concentrations in the deep sea. The harsh conditions and inhospitality of the underwater environment in general, as well as the inaccessibility of the abyssal zone for most human-made underwater vehicles, have hindered the study of this topic.

Underwater exploration is the exploration of any underwater environment, either by direct observation by the explorer, or by remote observation and measurement under the direction of the investigators. Systematic, targeted exploration is the most effective method to increase understanding of the ocean and other underwater regions, so they can be effectively managed, conserved, regulated, and their resources discovered, accessed, and used.Less than 10% of the ocean has been mapped in any detail, less has been visually observed, and the total diversity of life and distribution of populations is similarly obscure.

Types of exploration include investigation of the form and extent of the body of water or part thereof, investigation of the geological characteristics of the seabed and freshwater equivalents, and investigation of the geological structure, strata, and sediments underlying the body of water, investigation of the physical and ecological characteristics of the body of water and its containing geographical features, discovery and investigation of shipwrecks and archeological sites, and direct and remote visual observation of what is there.

A diving suit is a garment or device designed to protect a diver from the underwater environment. A diving suit may also incorporate a breathing gas supply (such as for a standard diving dress or atmospheric diving suit), but in most cases the term applies only to the environmental protective covering worn by the diver. The breathing gas supply is usually referred to separately. There is no generic term for the combination of suit and breathing apparatus alone. It is generally referred to as diving equipment or dive gear along with any other equipment necessary for the dive.

Diving suits can be divided into two classes: "soft" or ambient pressure diving suits – examples are wetsuits, dry suits, semi-dry suits and dive skins – and "hard" or atmospheric pressure diving suits, armored suits that keep the diver at atmospheric pressure at any depth within the operating range of the suit. Hot water suits are actively heated wetsuits.