Start up crash

As previously posted by the mods, this is a technical support problem. JIRA (where you're posting) is for bug reports.

Reposting this isn't going to get you too far (just kind advice).

If you've installed Java8, open up a terminal, type 'whereis java' (no quotes), it should respond with /usr/bin/java. If you run '/usr/bin/java -version' it should give you something similar to:
java version "1.8.0_40"
Java(TM) SE Runtime Environment (build 1.8.0_40-b26)
Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode)

Second, you have only allocated 1GB of memory when using a 512x512 texture pack. On the system you have, you will be getting around 5fps (if you're lucky). I only say this because I am running my MBP with 4GB dedicated to MC, on a Core i7, and it struggles to run 256x256 texture packs.

Thanks again Adam. Removing the pack has fixed it.