Mayor Island / Tūhua is a dormant shield volcano located off the Bay of Plenty coast of New Zealand's North Island. It lies north of Tauranga and covers . Geography The island is quite steep along its coast and rises to above sea level. A saddle about deep separates it from the North Island, while the other side of the volcano rises from the seafloor some beneath the waves. Approximately 18,000 years ago during the Last Glacial Maximum when sea levels were over 100 metres lower than present day levels, Mayor Island / Tūhua was connected to the rest of New Zealand. Sea levels began to rise 7,000 years ago, separating Mayor Island / Tūhua from the mainland. Hot springs abound, and there are two small crater lakes, Green Lake and Black Lake. These lie within two overlapping calderas formed in explosive eruptions 36,000 and 6,340 years ago. Geology Mayor Island is characterised as a peralkaline volcano and has exhibited a wide range of eruptive styles, including fire fountains, Strombolian explosions, extrusion of lava domes, phreatomagmatic explosions, Plinian falls and ignimbrite. The most recent lava flows have been dated at between 500 and 1,000 years old. The Tūhua Caldera formed in the > eruptive volume event of 6,340 years ago and also is a partial collapse crater. It is by in size. The Tuhua Tephra is quite distinctive and due to it having two dispersion patterns has been found in the Auckland area where it is up to 7cm thick, at Rotorua up to 10cm thick and Lake Waikaremoana where it is 4cm thick, making it useful as a mid-Holocene marker horizon. It has also been characterised from multiple sea bed cores off the East coast from the Havre trough off the Bay of Plenty to the southern North Island off Cape Turnagain. Te Paritu Tephra is assigned to a Mayor Island eruption but the full recent significant eruptive sequence required sea cores as prevailing winds are off land. In summary recent eruptions are: Risks The island would likely be sterilised in a typical major pyroclastic eruption at their current frequency of about every 7,000 years although a small eruption could be confined within the caldera. Tsunami activity and ash affecting the Bay of Plenty are possible with initial vent clearing and ash falls toward the major cities of the northern half of the North island being most likely in