I heard this from a USGS spokeswoman on television.

Problem:
The noun “phenomenon” is not plural.

Explanation:
The phrase “one of” should be followed by a plural noun.

The noun “phenomenon”, which means an observable occurrence, is the singular of the plural noun “phenomena”.

I believe that the use of “phenomenon” in place of “phenomena” represents hypercorrection. In particular, because so many people hear that “phenomena” is not always the correct noun, they use “phenomenon” even when “phenomena” is the correct noun.

Solution:
“One of the most deadly phenomena …”