yeast farty party would've been a much more concise answer

it's made using a process called the "Champagne method" or "méthode champenoise" which involves adding sugar and yeast to the wine and then bottling it before fermentation is complete. the yeast consumes the sugar and produces alcohol and carbon dioxide, which gets dissolved in the wine and can't escape because the bottle is sealed. this increases the pressure inside the bottle, making the wine bubbly. when you open the bottle, the pressure is released, and the carbon dioxide bubbles rise to the surface!

those bubbles appear to come from a specific spot because that is where the pressure inside the bottle is the greatest, which is typically the spot on the bottom of the bottle. hope that helps!