Abstruse:
Difficult to understand; obscure.
‘an abstruse philosophical inquiry’ [Oxford English Dictionaries]
Noted in “A cracking idea: The radical way to open up frozen seas,” David Hambling, NewScientist (10 March 2018, paywall):
It was an abstruse effect that went largely unnoticed until 1974, when the Canadian Coast Guard accidentally discovered what could follow. A team was testing whether an experimental hovercraft could break ice using the downwards pressure jets it uses to get around. But when the vehicle accelerated to just over 20 kilometres an hour as it travelled across the ice to a test site, the crew saw a wave form behind. The wave rose and rose – until the ice started breaking at its crest.
