Tonga eruption: Atlantic seafloor felt Pacific volcano megablast

The massive volcanic blast in the Pacific last year was felt 18,000km away on the other side of the world, on the floor of the Atlantic Ocean.

The cataclysmic eruption of Hunga-Tonga Hunga-Ha’apai on 15 January 2022 sent pressure waves through Earth’s atmosphere that connected with the sea surface and triggered 50 highly sensitive seismometers placed 5,000m under water on the seabed. It was one of a number of intriguing phenomena picked up by the instrument network in the Azores-Madeira-Canary Islands region.

Why are there continent-sized ‘blobs’ in the deep Earth?

In a strange corner of our solar system live two alien blobs.

With sprawling, amorphous bodies the size of continents, these oddities are thought to spend their time lying in wait for their food to rain down upon them – then simply absorbing it.

But their natural habitat is, if anything, even more unusual than their diet. It could be described as “rocky” – all around, there are exotic minerals in unknown shades and forms. Otherwise it’s fairly barren, except for a glittering sea in the far distance – one so large, it holds as much water as all of Earth’s oceans put together.

Every day the “weather” is the same: a balmy 1827°C (3321°F), with some areas of high pressure – equivalent to around 1.3 million times the amount at the Earth’s surface. In this crushing environment, atoms become warped and even the most familiar materials start to behave in eccentric ways – rock is flexible like plastic, while oxygen acts like a metal.

But this blistering wonderland is no extra-terrestrial planet – and the blobs aren’t strictly wildlife. It is, in fact, the Earth itself – just very, very deep underground.

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Land of opportunities

I admit that having grown up with Marvel comics, rock music and US TV shows, the American myth has accompanied me for almost all my life. Studying a scientific subject such as geology has also strengthened it, seeing that many of the fundamental discoveries have been made through Americans, while in Italy very little has been done and even less is being done for topics that concern my field of study. In fact, I had quite a few difficulties entering the working world as a geologist. Therefore, it was natural for me to see the USA as the land of opportunities even in geology. I was immature and I had no idea how the “system” worked in my country. If I had been aware of it, maybe I wouldn’t have missed the opportunities that came my way but that I recognized only in hindsight, when the train had already passed….

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An old Italian tragedy that left a scar – I was young and lived nearby

The southern Italy earthquake of 1980

It was a rather hot day for November. We teens and children were playing outside, in the courtyard and in the surrounding countryside. It was a beautiful autumn Sunday, sunny and cool, but not too much. In the afternoon there was the classic ball game in the courtyard. Our cheap but legendary Super Santos orange plastic ball, very common in Italy even today, had ended up in a balcony on the 2nd floor and one of us had climbed over from the stairs window to retrieve it. He took a risk that today as a parent would make my skin crawl. But over time we had all taken that risk in turn: the courtyard was surrounded by balconies and terraces on the ground floor, it was inevitable that the ball would end up in one of them. Sometimes we buzzed the owner to ask the favor to return it. More often, since the ball was easily confiscated, or worse, cut in two with scissors in a solemn ritual that they made us attend ruthlessly, we took the risk of climbing over before the owner noticed. When it went wrong, we would resort to a desperate fundraiser and rush to buy another one. In practice, we risked breaking and entering to avoid embezzlement by the flat’s owner. But that Sunday afternoon, November 30, 1980, the ball had ended up in the balcony of a friend of ours who no longer lived there, the apartment on the 2nd floor was uninhabited. So someone had to go to retrieve it despite its height of about 6 m…

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Stereonets and Rose Diagrams in Python

Geoscientists usually work with lines, planes and their angular relationships. Studying these relationships requires some techniques to put real 3D features into simple 2D visualizations. We don’t always need to design super complex 3D models just to figure out the angle between two planes, right?

This is why the Stereographic Projection and the Stereonets became so important to geologists. This projection is fast and efficient when we just want to analyze angular relationships. It does not preserve distances or areas of the features that are projected in it, just angles.

For today’s examples I will assume you already understand how a stereonet works and are familiar with:

  • strike and dip / plunge and bearing;
  • poles and planes

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How Mountains are Made

The surface of our planet varies greatly in altitude. In fact about ¾ are covered by seawater, whose average level has been conventionally chosen as a reference for the surface elevations. The statistical analysis of the elevations of the earth’s surface shows us something interesting: the highest percentage of the elevations is around two particular values that are the average level of the ocean floor (about -3790) and the average level of the emerged lands (about 840 m).

On the relative graph of the percentage distribution of the areas with respect to the altitudes, called “hypsographic curve”, it can be noted that the portions of surface that reach the minimum altitudes (about -11000 m of the Mariana Trench) and the maximum ones (8850 m of Mount Everest) are a very small fraction of the total.

In a nutshell, the mountain ranges are almost an exception, as are the oceanic trenches, on the surface of the Earth. They appear in so-called belts, which are considerably more developed in one direction than in the other. But what is it that keeps them standing at such exceptional altitudes compared to most of the land above ground?

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