A large sinkhole – or tomo – opened in a dairy farm near Rotorua a week ago. It happened after heavy rain – 170mm of rain in 38 hours. The sinkholes in this area are along earthquake fault lines which make pathways for water to fall along the fault lines. The hole underground swells and opens up. The result is a big crack in the land, 200m long, 20 to 30 metres wide and about 20m deep. This is as deep as the height of a 6-storey building.
The area around Rotorua is volcanic. The land is soft soil with a lot of pumice. There are nine other tomos in the area, but none so big. The farmer will need to fence this one off for safety.
Scientists who study volcanoes – volcanologists – say this is the summit of a volcano which erupted about 60,000 years ago. They are quite pleased to have the chance to study the layers of old lakebeds, and the layers of ash and pumice from the volcano eruption.
Vocabulary
sink (v) – fall down
sinkhole – a hole in the ground where the top layer of soil sinks into a hole
swell (v) – get bigger when filled with water
pumice – rock from a volcano; it is lightweight and contains air bubbles; it’s light grey in colour