Why? If you mine in tunnels you mine straight which means that the lava would flow towards you. Since the lava does that really slowly you can place blocks to prevent that from happening. That is also why I do not mine up or straight down.
With water you can turn it to obsidian, and if things do go wrong you can put yourself out. It's easier to make progress through a lot of lava by turning it into something you can walk on than it is to try to place blocks all over it.
And anyway if you were going to use a block against lava you'd be better off with sand or gravel, so you can fill up the lava pool from the top and then mine it out to see if there's anything good underneath. It's a lot easier to fill up a lava pool with blocks that have gravity.
Well it's mine if there were two lava towers nearby. Glad you recognized it to be a submarine. I think I should have made even longer because it looks a bit obese but I've already lenghtened it once so meh.
You mean Mojang with "they"? I guess never. Lego does not want that... they do not want creative games with their Logo on it. Years ago when Blockland looked like Lego the creator of this fantastic Game talked to Lego and after that he had to alter the game that it does not look like Lego anymore. The community (and I´m sure the creator) hoped, that there will be a deal with Lego. Unfortunately this did not happen.
Now, years after that I think I know why. Lego created Lego Universe. A game where you do not need any creativity at all, where you can´t build anything close to amazing. I think they do this on purpose... and hope that the only way to build fantastic stuff will be with Lego and not in computer games. But now we have Minecraft... and Blockland is still there (although it does look a bit awkward now) and Lords of Uberdark looks promising too.
Yeah I saw the beginnings of it months ago - I dug a tunnel for an hour or so and when I decided to surface I came up in the sea right next to it, but then it was just the outline. This time I was taking the long way home from my second home and BOOM - giant submarine!