State Highway 1 is the longest and most significant road in the New Zealand roading network, running the length of both main islands. It appears on road maps as SH 1 and on road signs as a white number 1 on a red shield, but it has the official designations SH 1N in the North Island, SH 1S in the South Island.

SH 1 is 2047 km long, 1106 km in the North Island and 941 km in the South Island. For most of its length it is a two-lane single carriageway, with at-grade intersections and property accesses, in both rural and urban areas. These sections have some passing lanes. There are sections of motorway in the vicinity of Auckland, Wellington, Christchurch and Dunedin.

SH 1 starts at Cape Reinga, at the northern tip of the Aupouri Peninsula, and since April 2010 has been sealed for its entire length. From Waitiki Landing south of Cape Reinga, SH 1 travels down the central-eastern side of the peninsula to Kaitaia, New Zealand's northernmost town, before turning south-east across the North Auckland Peninsula on to Kawakawa in the Bay of Islands, and then south to the city of Whangarei, the largest urban area in Northland.

New Zealand (Māori: Aotearoa) is an island country located in the southwestern Pacific Ocean. The country geographically comprises two main landmasses ‒ that of the North and South Islands ‒ as well as numerous smaller islands. New Zealand is situated some 1,500 kilometres (900 mi) east of Australia across the Tasman Sea and roughly 1,000 kilometres (600 mi) south of the Pacific island nations of New Caledonia, Fiji, and Tonga. Because of its remoteness, it was one of the last lands to be settled by humans.

During its long isolation, New Zealand developed a distinctive biodiversity of both animal and plant life. Most notable are the large number of unique bird species, many of which became extinct after the arrival of humans and introduced mammals. With a mild maritime climate, the land was mostly covered in forest. The country's varied topography and its sharp mountain peaks owe much to the tectonic uplift of land and volcanic eruptions caused by the Pacific and Indo-Australian Plates clashing beneath the earth's surface.

The following highways are numbered 1. For roads numbered A1, see list of A1 roads. For roads numbered B1, see list of B1 roads. For roads numbered M1, see List of M1 roads. For roads numbered N1, see list of N1 roads.

In Canada,

National Highway 1 (India)

A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite, or in an artificial explosion caused by humans. Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not made. Crater lakes covering active (fumarolic) volcanic vents are sometimes known as volcanic lakes, and the water within them is often acidic, saturated with volcanic gases, and cloudy with a strong greenish color. Lakes located in dormant or extinct volcanoes tend to have fresh water, and the water clarity in such lakes can be exceptional due to the lack of inflowing streams and sediment.

Lava lakes, a rare phenomenon where a volcanic crater can sustainably contain a significant volume of molten lava, are discussed in a separate article.

Crater lakes form as precipitation within the rim fills the created depression. The water level rises until an equilibrium is reached between the rate of incoming and outgoing water. Sources of water loss singly or together, may include evaporation, subsurface seepage, and in places, surface leakage or overflow when the lake level reaches the lowest point on its rim. At such a saddle location, the upper portion of the lake is contained only by its adjacent natural volcanic dam; continued leakage through or surface outflow across the dam can erode its included material, thus lowering lake level until a new equilibrium of water flow, erosion and rock resistance is established. If the volcanic dam portion erodes rapidly or fails catastrophically, the occurrence produces a breakout or outburst flood. With changes in environmental conditions over time, the occurrence of such floods is common to all natural dam types.