Janine Krippner
When researching large submarine landslides below our oceans, an alien example caught my attention.
About 51 million years ago a meteorite hit the continental shelf about 200 km south of Nova Scotia, Canada. This location is now buried under around 600 metres of sediment – so how do we uncover these dramatic events?
Researchers study the seafloor sediment and underlying rock using seismic data that ‘looks’ through the layers, often acquired during hydrocarbon exploration. Wells are drilled deep down through the layers and samples brought back to the surface.
These tools identified a submarine impact site for the first time. This was published in a 1987 research article, so is a pretty recent discovery.
The age of the impact was figured out by analysing rocks that melted during the impact, pinpointing the time they cooled back into glassy rock, very roughly speaking.
The impact formed a crater at least 45km wide and about 2.7km deep. For comparison, it is 42km from Ōtorohanga to Cambridge. The meteorite was calculated to be around 2.5-3.4km wide, assuming it travelled at a velocity of around 29km a second.
Janine Krippner
With something that powerful hitting the sloping seafloor, a significant portion of the slope collapses, causing widespread landslides.
Once all the rock and sediment stopped moving, it covered an area of around 93,000 square kilometres. Now this is a difficult area to imagine so to help, Lake Taupo covers around 610 square kilometres, and the area of the North Island is not quite140,000 square kilometres.
The landslide travelled an impressive distance, reaching out to 580km from the impact site. The drive from Hamilton to Wellington is about 525 km. These impressive numbers make this one of the largest landslides that we know of.
With these massive events, researchers unpack what happened like working through clues at a crime scene. A giant crime scene below the ocean, buried by 51 million years’ worth of sediment. Easy, right?
They considered how much material was displaced by the initial shaking, and how much was moved by the ensuing tsunami and the flow of water across the site. Where the meteorite hit, the water depth was somewhere around 300m. The movement of water would have eroded away surface sediments across the area.
Thankfully, we don’t have recent experience with large meteorite impacts, and they are pretty low on the list of things we will likely have to deal with. However, understanding these impacts and how they influence the land or seafloor around them is part of understanding how our planet evolved.
This helps put into context all of the more common processes, such as which landslides are caused by more likely events like large earthquakes.
Understanding all the complex parts of our geologic history gives important insight into the range of different processes that interact to shape our land and seafloor. It all matters.
May we all happily live our lives without ever witnessing one of these extraordinary events.
