Its magic.. duh!

Earthshakes? What earthshakes?

If you have DG and walk by one specific dwemer ruin a earthquake begins, I will not spoil why.

Oh, from the quest Lost to the Ages? I've already done it. What does it have to do with lava/magma?

No no its happened in another location just east of shearpoint near where the thieves guild quest line takes you and again near the store house at mzulft.

What really, does anyone know why.

From the depths of Nirn, a force greater than that of the dragons is building. The oblivious surface-dwellers feel the tremors and disregard their warnings with disdain, but for how much longer will their ignorance prevail? The Underworld's forces are marching, do you have the power to quell the tempest that rises from below? - The next Elder Scrolls expansion, Hearthfire! (We really don't know what's under the surface of Nirn beyond the dwemer and falmer...) But more to the point, the tremors must be caused by something.

I actually had a DLC idea based off the forge's Lava.
It involved just one massive (MASSIVE) mega dungeon, a sort of drill by the Dwemer, deep into the heart of Nirn. As you get deeper, the Falmer population disapears and the architecture starts becoming less ruined. You open up into a construction site, filled with lava.
Why you're down there? Idk. Maybe something to do with the Thalmor.
And no. I wouldnt want there to be Dwemer, or even an explaination. Morrowind told enough.
Idk, the atmosphere in thr Aetherim Forge was so amazing.

My friend who expierienced the same is the one whe actually told me about it and could not decide if it was thunder effect high up in the mountain regions but after expieriencing it for myself in 2 other locations other than Arkngthamz which does not actually explain exactly why the ground shakes all the time (Tonal locks require activation for an effect) its got me curious very. I maybe over thinking this but both the dwarves and snow elves are a big part of skyrim lore in the game you run into something to do with them all the time also the earthshakes only seem to happen very close to dwarven ruins. And I'm not ruling it out as a bug that came with the DG DLC but i kinda doubt it. It could be a new thunder effect but its exactly like outside of Arkngthamz so again i doubt it, Check it out i'd love to hear some solid confirmations.

Could it be a dragon or a mammoth, or something else natural? Correlation doesn't always imply causation, that's how superstitions are created... I'm going to go check out these tremors and see what's going on.

Ummm has everyone forgotten about the lava in the sky forge?

Have you seen the new magma for Dawnguard? It's completely different and it's only used at the end of a new mission for a boss battle. It just seems a little fishy to me is all.

I experienced this long before DG came out. Along the road to markarth yes?

What is it? Do you know?

Swimming in it is pretty cool.

Indeed...

The main use of this lava is to take care of Mjoll the lioness once and for all

If your have 100 percent fire resistance can you swim in the lava without losing health. Someone should test this out.

Doubtful, since resistances have a cap (IIRC it's ~85%).

With racial and standing stone bonuses I think it's possible.

I still believe the cap still takes effect at 85%, It stops people from becoming near immune to destruction magic.

Thanks, do potions affect anything?

But as a vampire you're susceptible to fire!

Aren't they locations in the same quest?

Well, if you think about it. he dwarves dug out all this earth so close to the magma vents in the planet. SO the earthquakes could just be the magma traveling though the tunnels. Seeing how the dwarves arnt there anymore to stop it from happening