- in the UK mountains are at least 2,000 feet high
- according to a UN program, mountain environments include places with "Elevation between 300 and 1,000 m (984 and 3,281 ft), with a 300 m (984 ft) elevation range within 7 km (4.3 mi)"
- according to the US Geographical Survey (USGS), there is no official definition of mountain
Continents are messy, because landmass on Earth is messy, it's contiguous where it looks like it isn't and so on.
A more surprising thing (at least IMHO) is that different countries have different definitions of... mountains.
I'm not a geologist but if we can trust Wikipedia (https://en.wikipedia.org/wiki/Mountain):
- in the UK mountains are at least 2,000 feet high
- according to a UN program, mountain environments include places with "Elevation between 300 and 1,000 m (984 and 3,281 ft), with a 300 m (984 ft) elevation range within 7 km (4.3 mi)"
- according to the US Geographical Survey (USGS), there is no official definition of mountain