Story: Geology – overview
Page 11 – Holocene – the last 10,000 years
The Holocene period, covering the last 10,000 years, is characterised by a warm and relatively stable climate. Nevertheless, the pace of uplift and land deformation, dictated by the movement of the Pacific and Australian plates, has ensured that geological change within New Zealand has remained extremely rapid.
Warming climate, rising seas
Beginning about 18,000 years ago, earth started to emerge from the latest glacial period. As the climate warmed, water from the planet’s ice caps poured back into the oceans and their level rose. Sea level reached a maximum at about 7,000 years ago (about 5000 BC), and has remained stable since then.
The rising sea flooded low-lying areas, and in many places in New Zealand, extended well inland of the present coastline. Since then the coast has built outwards in many places, as sediment eroded from the land has been carried by rivers to the ocean. Waves and currents have distributed this sediment along the coast. Long spits have formed, connecting areas of land and building across the heads of bays, and forming features such as Farewell Spit and the Kaitorete barrier beach damming Lake Ellesmere.
Activity in the central North Island’s volcanic zone has continued unabated into the Holocene period. About 1,800 years ago the Taupō caldera unleashed the most powerful volcanic eruption on earth in the past 5,000 years, incinerating over a sixth of the North Island. Tongariro, Ruapehu and Taranaki have erupted intermittently, spreading fine ash over the surrounding countryside, and the striking volcanic cone of Ngāuruhoe has been built entirely within the last 2,500 years.
During the Holocene period several volcanic cones have been added to Auckland’s skyline, including Mt Wellington. The formation of Rangitoto was witnessed by Māori about 600 years ago.
Deformation of the land
Accompanied by frequent earthquakes – mostly small but sometimes destructive – the continent of Zealandia is being compressed along the boundary between the Australian and Pacific plates. Squeezed between the converging plates, the crest of the Southern Alps is currently rising at an estimated rate of 10 millimetres per year. This rise is not smooth – in large earthquakes, blocks of land may rapidly lurch several metres upward. Sections of countryside may also move many metres horizontally – in the magnitude 8.2 earthquake of 1855, land shifted up to 18 metres along the Wairarapa Fault.
Not all of New Zealand is rising. The north-east corner of the South Island, on the edge of the Taranaki basin, is subsiding. Here the sea has flooded into former river valleys, creating the maze of waterways of the Marlborough Sounds.
The Holocene period is sometimes known as the Anthropogene or the Age of Man. Although our own species, Homo sapiens, appeared well before the start of the Holocene, this period encompasses all of humanity’s recorded history. New Zealand was one of the last land areas in the world to be settled by humans, with the arrival of Māori about 1250–1300 AD and Europeans from about 1790.
Humans have had an immense impact on the natural environment of New Zealand in only 700 years. Forest-burning and conversion of land to agriculture has removed over two-thirds of the native forest, causing major ecological changes and accelerating erosion. Hunting and the introduction of alien plants and animals has led to the extinction of native species. Future geologists will recognise the impact of humans in New Zealand as a sudden change in the record of rocks and fossils.