Mysterious blobs deep inside Earth may fuel volcanic eruptions

Explosive volcanic eruptions don’t just damage property and cancel flights.

They can kill hundreds or even thousands of people, burying them under lethal ‘pyroclastic’ flows. 

Now, scientists in Australia have identified a possible cause of gigantic volcanic eruptions – mysterious ‘blobs’ about 1,200 miles under our feet. 

Blobs are three-dimensional regions that span the length of continents and stretch 100 times higher than Mount Everest. 

They sit at the bottom of Earth’s rocky mantle above the molten outer core – a place so deep that Earth’s elements are squeezed beyond recognition. 

And they’re a starting point for plumes of hot molten rock which flow upwards towards the Earth’s surface. 

There they erupt as lava, gases and rock fragments – with the capability of wiping out life as we know it. 

The authors warn that giant, large-scale eruptions can have serious impacts, such as sudden climate change and mass extinction events. 

Volcanic eruptions can intensify global warming by adding greenhouse gases such as carbon dioxide (CO2) to the atmosphere. 

Giant volcanoes also triggered events that led to the largest mass dying on Earth, the Permian-Triassic extinction 252 million years ago. 

‘These blobs have possibly existed for hundreds of millions of years,’ say the researchers from the University of Wollongong near Sydney. 

Earth is made up of three layers – the crust, the mantle and the core, which was recently separated into ‘inner’ and ‘outer’.

According to the team, blobs are at the bottom of Earth’s mantle, about 1,200 miles and 1,800 miles (2,000km and 3,000km) below our feet.

The mantle, the planet’s thickest layer, is predominantly a solid rock – but blobs may be different compared with the surrounding mantle rocks. 

Blobs are made of rock just like the rest of the mantle, but they’re thought to be hotter and heavier. 

For their study, the team used computer modeling to simulate ‘mantle convection’ – the movement of material in Earth’s mantle powered by heat – over one billion years. 

Their findings suggest that mantle plumes – columns of hot molten rock in the mantle – rise up from the continent-sized blobs. 

Mantle plumes are shaped a bit like a lollipop sticking upwards – with the ‘stick’ the plume tail and the ‘candy’ nearer Earth’s surface the plume head. 

The researchers found that locations of volcanic eruption fall either onto (or close to) the location of blobs, as predicted by their models. 

This suggests that blobs – an acronym standing for Big LOwer-mantle Basal Structures – are essentially the deep-Earth origin of volcanic eruptions. 

Typically, deep Earth motions are in the order of 0.4-inch (1 cm) per year, so they only become significant over tens of millions of years. 

Blobs probably shift in a year at roughly the rate at which human hair grows each month, the team say. 

Although they have possibly existed for hundreds of millions of years, it’s unclear what causes their movement. 

Mantle plumes rise very slowly from blobs through the mantle because they transport hot solid rock, not melt or lava. 

At lower pressures in the uppermost 125 miles (200 km) of Earth’s mantle, the solid rock melts, leading to volcanic eruptions.

‘We used statistics to show that the locations of past giant volcanic eruptions are significantly related to the mantle plumes predicted by our models,’ explain the authors in a piece for The Conversation. 

‘This is encouraging, as it suggests that the simulations predict mantle plumes in places and at times generally consistent with the geologic record.’ 

The new findings, published in Communications Earth and Environment, suggest that the deep Earth is even more dynamic than we realised. 

Future research aims to explore the chemical nature of blobs, which might be possible with simulations that track the evolution of their composition.