After getting the Blue Pikmin, go to the Impact Site. Go to the area nearby with three “10” Pellets of each color. Take a few Blue Pikmin and take them near to have them attack something on the ground. They’ll uncover a geyser that will get you up there. Toss the Pikmin up there before going on the geyser. Take more than 10 Pikmin in case a few fall off.