Here is the full list of all 20 Alto's Adventure (Windows) achievements worth 1,000 gamerscore.
You completed all 180 goals.
You played as Tupa.
you rode for 1,000,000m (cumulative).
You played as Felipe.
You played as Izel.
You snowboarded for 30 in-game days (cumulative).
You recovered 1,000 llamas (cumulative).
You played as Paz.
You rode for 100,000m (cumulative).
You played as Maya.
You snowboarded for seven in-game days (cumulative).
You rode for 10,000m (cumulative).
Your board stuck straight up after a crash. Oops!
You played one run with Alto.
You completed the tutorial.
Snowboard for five in-game years (cumulative).
Snowboard for 365 in-game days (cumulative).
Recover 10,000 llamas (cumulative).
Recover 100,000 llamas (cumulative).
Ride for 10,000,000m (cumulative).