The most common and most likely answer to this crossword clue is the 10 letter word QUICKSANDS
I've seen this crossword clue in The Guardian
Q
U
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S
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Buddy explains!
The straight part
We know that "Hazard on coast /Hazard on coast" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hazard on coast /hazard on coast = quicksands.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does QUICKSANDS mean?
QUICKSANDS noun- Wet sand that things readily sink in, often found near rivers or coasts
- Anything that pulls one down or buries one metaphorically