Buoyant

And of course, in order to understand the Earth's past and how it got to where it now is, it is important to have a basic knowledge of plate tectonics, which explains how the planet's continental and oceanic crusts are part of the lithospheric plates that are buoyant and ride upon the highly viscous asthenosphere.

I’m in a buoyant mood.

[...] the accelerated, high-frequency East Coast express timetable, operating this year in a buoyant economic environment, is beginning to attract more business travel to rail (although there is still a long way to go before the potential is fully realised); [...].