ln some parts of the world, violent earthquakes sometimes make the ground open up and swallow people. My question is: is there a word or phrase to describe this appalling scene?
The following biblical passage uses language very similar to your own:
the earth opened its mouth and swallowed them and their households, and all those associated with Korah, together with their possessions (Numbers 16:32)
This passage should convince you that there is nothing wrong with plainly saying "the earth swallowed the people."
You could also say:
the earth opened its maw to swallow them
where maw means "the jaws or throat of a voracious animal."
You could also say:
The earth devoured them
where devour means "eat (food or prey) hungrily or quickly."
All of these examples anthropomorphize the earth (that is, depict the earth with human characteristics like having a mouth). There is nothing wrong with this technique and it can be quite effective, especially when combined with evocative words like maw and devour, which connote viciousness and gluttony.
Engulf is a good word for this. American Heritage:
To swallow up or overwhelm by or as if by overflowing and enclosing: The spring tide engulfed the beach houses.
More generally, a scene like that might be described as a cataclysm.
something that causes great destruction, violence, etc.
(from Merriam-Webster's Learner's Dictionary)
1: to enclose or enfold completely with or as if with a covering
tr.v. en·vel·oped, en·vel·op·ing, en·vel·ops
1. To wrap, enclose, or cover: "Accompanying the darkness, a stillness envelops the city" (Curtis Wilkie).
2. To surround: The troops enveloped the town.
This term gives a visual of the ground rising up and surrounding the people, much like engulf.
You might say:
During the earthquake, the ground opened up and enveloped the people.
Note that this is not pronounced like 'envelope'. The emphasis is squarely on the second syllable.
I'd suggest subsume. It means absorb, and its origin is the latin subsumere, whose parts roughly translate to take from below.
Include or absorb (something) in something else
The National Post is reporting that all four members of the Prefontaine household have died after their house was subsumed by a sinkhole.
To be honest though, I think simply using swallow is more commonly used. If you google "killed sinkhole", you will find article after article saying that some person was swallowed by a sinkhole.