I've seen a few minor arkfalls over the last few days, where there's no crystal, just a mass slaughtering of skitterlings before the timer runs out.
Yeah I've been to a few of those too... weird. The little skitterlings just keep spawning, people were having a blast squishing them with their cars/quads.
Really? It's that simple? If so that's just weird... I think I do have a purple cluster in my arkfall loadout... will try something else tonight and see what happens!