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On June 30, 1908, an asteroid (or possibly a comet) entered Earth’s atmosphere over a Siberian forest near the Podkamennaya Tunguska River at high speed. It was about 50 – 100 meters across, and likely made of fragile material, which is common for small asteroids. The huge pressure involved with ramming through air at something like 20 kilometers per second caused the rock to crumble and burn up extremely rapidly, releasing all its vast kinetic energy — the energy of motion, and it was moving — in essentially one giant burst: an explosion.

The explosion — now called the Tunguska Event or Impact — was equivalent to a 10-megaton bomb, detonated several kilometers above Earth’s surface. This created a massive shock wave that traveled downwards, expanding in a spherical shell. The shock wave touched down first directly under the explosion, then spread out in all directions in a circle of increasing diameter (see the image here, amazing artwork by Don Davis that shows a scientifically accurate depiction of the event).

This created a weird effect: directly under the blast the force of the explosion was straight down, so trees at that position weren’t blown over, but they did have their leaves and branches stripped away. But just meters away from that point the force of the blast started to take on more of a sideways force, and was able to knock trees down. This created a huge area of felled trees, pushed over by the force, and they all pointed away from that central blast point, ground zero. Expeditions sent to the site later saw this bizarre sight, and I can only imagine what they felt as they approached it. Mind you, the first expedition was in the 1920s, well before atomic bombs (it wasn’t until much later that nukes detonated in airburst tests gave scientists the insight they needed to understand Tunguska).

However, that was over a century ago, and it happened in a forest. Over that time, nature recovered:

This Landsat satellite image taken in July 2024 shows the region (the point directly under the blast, the epicenter, is labeled, as well as a possible trajectory for the incoming asteroid). Clearly the trees have grown back.

I got this image from the wonderful NASA Earth Observatory Image of the Day, which has a lot of really interesting details about the event.

 I live in a forest now, and you can’t walk too far without seeing a tree that’s fallen over. Virginia gets hot and humid, so it doesn’t take too long for bacteria and fungus and other beasties to break down the tree, and new trees take its place rapidly. Still, it’s surprising to me that in just 112 years there’s little sign left that the Tunguska impactor ever exploded there — it didn’t leave a crater because it was an airburst, blowing up high above the ground, and no material from the asteroid has ever been definitively found.

Big impacts can change life on Earth for millions of years, like the Chicxulub impact 66 millions years ago. Others are healed over pretty quickly. I can think of several metaphors here; feel free to come up with your own.

But one good thing came from this: Asteroid Day, a global event to raise awareness about asteroids, their uses, and their dangers. I strongly support this effort (only hospitalization kept me from participating in Luxembourg in 2022) because I understand that the threat is real, but so is the science we can reap from studying these rocks.

 BANners who have followed me long enough know I love images of volcanoes taken from space, and it’s been a good while since I’ve posted one. So, to make up for that delay, here is an amazing one, just truly incredible!

Wow! Like with Tunguska, I also saw this on the wonderful Earth Observatory Image of the Day site, which as always I strongly recommend. It’s a terrific way to see our planet.

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