Chicxulub Asteroid – Tsunami and Earthquake
The Chicxulub-derived mega-tsunami that struck New Zealand 66 million years ago is a remarkable example of long-distance geological devastation.
Originating from the asteroid impact that caused the Cretaceous-Paleogene (K-Pg) Extinction, the tsunami travelled almost 12,000 km from the Chicxulub crater in Mexico to New Zealand’s east coast. Because South and North America were then separated by open sea, the wave had unhindered access into the South Pacific.
Our guest speaker, Prof Chris Hollis, had been studying Wairarapa geology, particularly around Tora, when he became associated with a landmark global modelling study led by the University of Michigan that mapped how the waves reached New Zealand and what they left behind. (See A Wave from Our Past, Wairarapa Times-Age, 5 October 2022.)
When the asteroid, about 12 km wide, struck the Yucatán Peninsula at an estimated 20 km/s (72,000 km/h), it triggered a magnitude 11-12 earthquake and generated an initial wave up to 4.5 km high. The energy travelled southwest across the Pacific towards Zealandia, reaching it within 24 hours. In the open ocean the waves exceeded 10 metres, but as they approached the shallow continental shelf they slowed, grew in height, and came ashore with far greater force. Seven waves are thought to have struck the coast.
For decades, geologists had noted unusual, heavily disrupted rock formations on New Zealand’s east coast dating precisely to the K-Pg boundary. These thick, chaotic deposits of rock fragments and jumbled marine sediments were originally attributed to tectonic activity or underwater landslides. However, tsunami models showed the Chicxulub wave generated seafloor flows powerful enough to scour the ocean floor, rip up sediments and leave a permanent geological record.
New Zealand’s east coast deposits are now regarded as some of the strongest physical evidence of the scale of the Chicxulub impact tsunami.
The South Wairarapa Rebus Club meets at 9.45am on the fourth Friday of each month at the South Wairarapa Working Men’s Club in Greytown. Retired people are invited to attend as visitors. Contact John Reeve on 021 560 461 for more information.
