While each volcano is unique they can largely be divided into red volcanoes and grey volcanoes.

Red volcanoes typically have effusive eruptions dominated by the classic red-glowing lava flow or lava lake. The constant mild eruptions of lava let gases escape reducing the chances of gas build-up and larger explosions. A classic red volcano is Kīlauea in Hawaii.

Grey volcanoes are known for explosive eruptions. Trapped gases and heat can build up within the volcano releasing explosive eruptions that can shoot ashes and rock high into the sky and cause fast-moving pyroclastic flows of solidified lava and ash. Grey volcanoes are typically much more destructive than red volcanoes and can exhibit some behaviours like their red counterparts. A classic grey volcano is Mt St Helens.

I learned this distinction from the remarkable film Fire of love.

Order of adjectives (came to mind as I wrote 'classic red-glowing lava flow' - try the adjectives in other orders =) )

Red volcano, grey volcano

Which is kind of amazing. The magnetic field is produced by some remarkable result of the convection of molten hot iron alloys in the core of the Earth. Kind of hard to really get your head round if you’re sitting calmly at your desk or walking on a nice stable surface. Periodically, the poles switch round it seems but at the moment the magnetic South pole is actually near the point we’d normally call the geographical North pole. They’re pretty close, but the geographic axis doesn’t exactly coincide along the geographic axis of rotation of Earth. And the lines of force go from magnetic North to magnetic South so your compass needle is actually pointing towards magnetic South. Remember iron filings and bar magnets from physics class?

Earth is a big magnet.

How do you remember which are stalactites and stalagmites in a cave? And how to spell them?

The key to getting the whole thing the right way round in my mind is to remember that you need to cling tight (tite) to the ceiling. Once that’s established, you have a letter C in stactite that fits cling and ceiling. And stalagmites, with its cheeky G, naturally then is the other one which would grow on the ground. Sorted?

Stalactites, Stalagmites

Meteor: A rock burning up as it enters the atmosphere. Also known as a shooting star.

Meteorite: Parts of a meteor that made it all the way to the ground. Look out!

It was a long time before I really knew the difference between these things.

Asteroids, meteors and meteorites

Divergent (Mid-Atlantic ridge, The Rift Valley), Convergent (The Andes, The Himalayas) and Transform (San Andreas fault, Dead Sea Transform). There are some sub-varieties but these are the main ones. This makes natural sense, so there’s no remembering to do, when you have two contacting plates: they can either be pushing together, pulling apart or rubbing past each other.

Incidentally, the idea that the giant continents move around all the time, enough to pull apart South America and Africa, and thrust up the Himalayas, obvious as it may seem now, was once not at all obvious. And if you stand on the ground in a big landscape, it’s kind of amazing to think of just what an amazing notion it was to propose.

I read about it in Bill Bryson’s, A Short History of Nearly Everything for which I found a relevant excerpt online - The Earth Moves (pdf) - should you be interested in the characters that had the courage to seriously propose it.

Tectonic plate interaction boundaries

A large boulder, transported and deposited by a glacier. This is my favourite location for glacial erratics. Bonus points if you can tell where it is.

Glacial erratic

The Mediterranean sea was formed kind of how you think it might have happened from just looking at a world map — the mighty Atlantic ocean breaking free to fill up the giant basin from the African continent pushing into Europe.

I imagine it somewhat like the footage of when the sea reclaimed a tin mine in Malaysia in a few short minutes. Or when the waves finally overcame the walls of my sandcastle, just at a staggering scale.

Sketchplanations tagged with geology