The cause is very likely to be a large volcanic eruption (consistent with ice-core evidence), and the most likely eruption is Thera.
(The cause; is; very likely to be a large volcanic eruption (consistent with ice-core evidence) (The cause; to be; a large volcanic eruption (consistent with ice-core evidence) (the most likely eruption; is; Thera)
The cause The cause the most likely eruption
is to be is
very likely to be a large volcanic eruption (consistent with ice-core evidence
a large volcanic eruption (consistent with ice-core evidence
Thera