Is it plausible for a landmass to shatter in a tectonic/volcanic cataclysm?

Question

In George R.R. Martin's A Song of Ice and Fire novels, the land of Valyria was transformed from peninsula to archipelago by a volcanic cataclysm followed by earthquakes, tidal waves, a miasma of smoke and gas, and storms of obsidian shards. Excepting the obsidian storms, cool as they are, is this a plausible scenario? Could chained tectonic disasters of an intensity which could plausibly be imagined on Earth rend a contiguous landmass of several hundred kilometers to a side asunder? Could the ocean fill the rents, creating many islands and a new sea? Could all this happen in the space of a couple days?

For the purposes of this question, let's choose a specific landmass on Earth and test the plausibility of this scenario against it's (ever so slightly terraformed) geography. In the novels, Valyria is depicted as being peninsular, near-equatorial, and kinda Greece-shaped.

Valyria before the Doom:

Valyria after the doom:

So let's choose a peninsular, near-equatorial (sorta), Greece-shaped landmass. Perhaps Greece?

Let's assume that our "Greece" has astonishingly active tectonics and vulcanism. Lots and lots of vulcanism. At least 14 active volcanoes on the mainland, ideally more. With a tectonics & vulcanism budget limited only by the number of volcanoes and fault lines that can feasibly fit in "Greece" (with at least nominal regard to what is plausibly believable of nature), can we destroy our peninsula and make it into even more islands? Other tectonic lines of the planet can be bent, erased, or added to facilitate our project, so too for any other geographical feature that needs to be altered. Lastly, what could trigger that series of eruptions, what sort of tectonic action needs to occur for everything to go boom at once?

Answer 1

If you mean an entire continent, then I am afraid, NO

No matter how much of a volcano you get, you won't be able to dent a single hole in a continent-sized landmass. You could have like 10 Yellowstone-sized supervolcanoes erupting at full power, and it would be a measly fart to a gargantuan landmass the size of North America or Asia.

However, you still may have some luck with island groups and small peninsulas. For example, the 1883 Krakatoa eruption caused nearly 70% of the landmass of the island of Krakatoa to cave in due to caldera collapse.

However, the point remains. Volcanoes may be threatening for small islands and stuff, but even the strongest, mother-of-all-supervolcanoes (MOAS??) can't even dare to register a single pockmark, much less shatter, on a massive continent-sized landmass.

The only thing that comes close to actually disrupting crustal features are large asteroids, and even then, Dinosaur-Killer didn't exactly rip Mexico apart, did it? The best you're going to get is some ugly crater sticking out of the continent, but aside from that, you can't actually tear an entire landmass.

The only thing that actually can tear continents apart are tectonic plates, as in the case of the Keewenawan rift, which actually came close to tearing North America apart into two landmasses.

Still tho, volcanoes don't have the b*lls to shatter a giant landmass.

Back to the question

Greece, while it may seem small, is still pretty huge as a landmass. While it certainly isn't continent-sized, it is still formidable enough to not be torn apart by volcanoes.

Rest assured, you may be able to flood some areas of your "Greece" as the volcano collapses, and form some isolated islands out of the landmass. But, shattering a landmass? Impossible.

Answer 2

Usually earthquakes are one plate sliding past another plate. The energies released may be enormous but the action movement may be only a few metres. You can see this in the video of the Nepal 2015 7.8 Earthquake. Or rather, you can see the waves and the shaking but the actual plate movement is pretty small. This may dislocate roads, but you may be able to walk across the join between the plates.

You can get subduction earthquakes where the land goes up and down. This could cause the land on one side to flood. Some of these are called Megathrust Earthquakes because of the enormous energies released. However, have a look at the pictures of the Alaska 1964 9.2 earthquake. One side of the fault has gone down by 3 metres. It could create flooding, but not very deep flooding.

The 'Smoking Sea' suggests a line where two plates are moving apart, much like happens in Iceland. This has volcanoes, but does not tend to have huge earthquakes as it is making new tectonic plates rather than trying to move existing ones.

Here is an animation of the breakup of Pangea. Tectonic motion can rip apart continents, but it tends to happen as an enormous sequence of small movements, rather than everything at once.

Answer 3

The Isthmus of Corinth is the key to having a single event split Greece. This Isthmus is already breaking Greece apart as it is part of a rift that formed the Gulf of Corinth and is spreading apart at the rate of 10mm per year. https://en.wikipedia.org/wiki/Gulf_of_Corinth Volcanoes are common on the sides of rifts. Greece has Methana on that gulf which last erupted in 230 BC. https://en.wikipedia.org/wiki/Methana_Volcano An eruption would be the consequence of the rift moving, not the cause.

To have a significant land mass be split by earthquake, it would first have been split by a rift that hadn't been open to the sea. The rift would lower land in the middle to quite a bit below sea level (think Death Valley or the Dead Sea valley). That would take a few million years to develop. Then, have a large earthquake open the door to the sea to flood the rifted land.

It tends to be quite difficult to get nearby volcanoes to erupt in unison. In order to erupt in unison, they all need to have sufficient magma AND sufficient gas build up under them at the same time. It is far more common for a chain of volcanoes to erupt over several hundred years. When we look at places where land masses have split apart, we see the combined actions of millions of years, not a few weeks.

When the land is split apart and volcanoes erupt, a good number of them are basaltic eruptions like the rift eruptions in Iceland - small fire fountains and fast-moving lava flows like the recent eruptions there. Explosive eruptions happen where continental land is melted, and the lava has a lot of silicon in it.