Cook Strait

Cook Strait is a vital waterway in New Zealand.

It separates the North Island from the South Island. This strait connects the Tasman Sea in the northwest to the South Pacific Ocean in the southeast. It is known as one of the most dangerous and unpredictable bodies of water in the world. Because of its location, it has played a massive role in the history and movement of people in the region.

The water in the strait moves in a very unusual way. This is caused by the lunar semidiurnal tide, also known as the M2 tide. This tide circulates anti-clockwise around New Zealand. Because of this pattern, the tidal elevation at each end of the strait is almost exactly out of phase. This means high water on one side meets low water on the other side. On the Pacific Ocean side, high tide occurs five hours before it occurs on the Tasman Sea side. This difference can drive tidal currents up to 2.5 metres per second.

The seafloor, or bottom topography, is also very complex. The strait has an average depth of 200 metres. To the east, the Cook Strait Canyon has steep walls that descend into the Hikurangi Trough. To the northwest lies the Narrows Basin, where the water is deep. The bottom is particularly irregular near the South Island coast. Islands and underwater rocks create violent eddies in the water. These submarine ridges make the ocean flow even more turbulent.

History and discovery of the strait involve many different cultures. Māori legend says the navigator Kupe discovered the area. He followed a monstrous octopus named Te Wheke-a-Muturangi across the water. In 1642, the Dutch explorer Abel Tasman saw the area. He believed it was a closed bay and named it Zeehaen's Bight. In 1769, James Cook proved it was a navigable strait. The waterway was later named in his honor.

Human activity has changed alongside the strait's history. In the early 19th century, the area attracted European settlers. Whalers established bases in the Marlborough Sounds and the Kāpiti area. They were drawn by the whale migration routes. From the late 1820s until the mid-1960s, Arapaoa Island served as a whaling base. In the 1820s, Te Rauparaha led a Māori migration to the region. Later, permanent settlements grew at Wellington, Nelson, and Whanganui.

The strait has also been a place of significant maritime and geological events. Many ships have been wrecked there, including the Maria in 1851 and the SS Penguin in 1909. The area is also prone to earthquakes. A severe earthquake struck both sides of the strait in 1855. In 2013, two large earthquakes measuring 6.5 and 6.6 on the Richter Scale struck the area. These events caused damage in Seddon and Wellington.

Many animals rely on the strait as a habitat. It is home to killer whales and several dolphin species. These include bottlenose, common, and dusky dolphins, as well as the endemic Hector's dolphin. A famous Risso's dolphin named Pelorus Jack lived here from 1888 to 1912.

He was known for escorting ships through the water. Near the east coast, the Brothers Islands provide a sanctuary.

North Brother Island is a safe place for the rare Brothers Island tuatara.

Finally, the geography of the strait has changed over thousands of years. About 18,000 years ago, sea levels were much lower. During this time, the North and South Islands were connected by land. The Cook Strait was actually a deep harbour of the Pacific Ocean. About 7,000 years ago, sea levels began to rise. This rise eventually separated the islands and created the strait we see today.