Lake Taupō

Lake Taupō sits inside a volcano.

The volcano threw rock far away. Then the ground sank, and water filled it.

GeoNet, New Zealand's hazard monitoring service, says Taupō volcano began to erupt over 300,000 years ago. It has many vents, and most of them are now under the lake.

Taupō is not a mountain. Its eruptions were so explosive that the rock was thrown far from the vents, and the ground then collapsed to form a caldera, a collapsed volcano. Today New Zealand's largest lake fills it.

Taupō volcano first began to erupt over 300,000 years ago and has many vents, most now under the lake (GeoNet). Geological studies show the volcano makes up only the northern half of the lake and a small surrounding area, with numerous eruptions from different sites.

Taupō is not a large mountain because its eruptions were so explosive that material was deposited far from the vent, and the ground then collapsed to form a caldera. IAGLR lists the lake's origin as both tectonic (faulting) and volcanic (caldera).

Long ago, Taupō volcano erupted and threw out pumice.

Pumice is a rock made by volcanoes. You can still find it on beaches.

Over 1,800 years ago, the Taupō eruption burst from a line of vents near the eastern side of today's lake. GeoNet calls it the most violent eruption in the world in the last 5,000 years.

It dropped five layers of pumice and ash across the central North Island, then an energetic flow of pumice and ash, called a pyroclastic flow, filled the main river valleys. The pumice can still be seen today, rivers carry it when they flood, and rounded pumice on North Island beaches came from this eruption.

The Taupō eruption, over 1,800 years ago, came from a line of vents near the eastern side of the modern lake; GeoNet calls it the most violent eruption in the world in the last 5,000 years. Its first phases laid down five pumice and ash fall deposits over the central North Island, especially to the east.

It ended with an energetic pyroclastic flow that swept over about 20,000 km² and filled the major river valleys with pumice and ash. Rivers still carry this pumice in flood, and rounded pumice on North Island beaches comes from it.

About 30 rivers flow into Lake Taupō.

Only one river, the Waikato, flows out.

ILEC says about 30 rivers flow into Lake Taupō, and the Waikato River is its only outlet. The town of Taupō sits where the Waikato River leaves the lake.

ILEC's records give the lake a maximum depth of 164 meters and a volume of 60 cubic kilometers. Its water is clear, with a maximum transparency of 21 meters: you could see that far down. It has remarkably little nitrogen, which keeps the lake low in nutrients.

About 30 rivers flow into the lake and the Waikato River is its only outlet (ILEC). ILEC lists a maximum depth of 164 m, mean depth of 91 m, volume of 60 km³, shoreline of 153 km and water residence time of 10.6 years; IAGLR gives a maximum depth of 159 to 164 m.

The water is clear and highly transparent, with a maximum transparency of 21 m. Nitrogen and the nitrogen-to-phosphorus ratio are remarkably low, which ILEC says may be mainly due to the catchment's geology and makes the lake oligotrophic.

Two kinds of fish, koaro and toitoi, are native to the lake.

Rainbow trout were brought here and live there too.

ILEC names the koaro and the toitoi as fish native to Lake Taupō. The koaro, with a flat head and tough, slimy skin, was an important food fish for the Māori people living around the lake, but it has become very scarce.

Rainbow trout were stocked in the lake by people and are now abundant and mainly important for sport fishing. The common smelt was brought in between 1934 and 1940.

Native fish include the koaro and the toitoi (ILEC). The koaro, flat-headed with tough but slimy skin, was an important fish resource for Māori living around the lake but has become very scarce.

Artificially stocked rainbow trout are now abundant and mainly important for sport fishing; the common smelt was introduced between 1934 and 1940 after the average size of trout declined. Submerged plants include Chara and Nitella.

Wear a life jacket in and around a lake.

Always swim with a buddy and a grown-up watching.

The US Centers for Disease Control and Prevention (CDC) says children should wear life jackets for all activities in and around natural water such as lakes. A grown-up should watch children closely the whole time they are in or near water.

Lakes can have hidden hazards such as currents, waves, rocks, plants and water you cannot see through, so always swim with a buddy. Swimming lessons help too.

The CDC advises life jackets for children in all activities in and around natural water, close and constant supervision by a designated adult (even when lifeguards are present), and the buddy system.

Lakes, rivers and oceans have hidden hazards such as dangerous currents or waves, rocks or vegetation and limited visibility. Formal swimming lessons can reduce the risk of drowning, but children who have had them still need close supervision.