Never seen this happen before. Both of these were arrival burrows.

You feel a rumble come from beneath your feet.
You come out of hiding.
The floor begins to shiver slightly, casting thin ripples across the landscape. As the protuberances increase in intensity, an enormous rift crawler launches to the surface from within! The crawler's massive maw lies agape, its glistening obsidian teeth gnashing at everything in their path!
You take the brunt of the blow from the crawler's massive body, narrowly avoiding its razor-sharp teeth!
... 20 points of damage!
Good blow to your right arm!
You are stunned for 2 rounds!
The crawler lurches through the air before finally landing with a solid thud.
You feel a rumble come from beneath your feet.
The floor begins to shiver slightly, casting thin ripples across the landscape. As the protuberances increase in intensity, an enormous rift crawler launches to the surface from within! The crawler's massive maw lies agape, its glistening obsidian teeth gnashing at everything in their path!
You take the brunt of the blow from the crawler's massive body, narrowly avoiding its razor-sharp teeth!
... 10 points of damage!
Blow connects right below your right eye!
The crawler lurches through the air before finally landing with a solid thud.

That sure sucks, what I like is when you know there is one burrowing, a crawler pops up, feint and another one burrows up.