Why when ammonia gas is bubbled into water the solution has such a high pH value?

When ammonia gas is bubbled into water, it reacts with water to form ammonium hydroxide, which is a strong base. The presence of ammonium hydroxide increases the concentration of hydroxide ions in the solution, leading to a high pH value. Ammonium hydroxide equilibrium with its ionic components NH4+ and OH- contribute to the alkaline nature of the solution.