Land on Brink Island and search volcano for eco seeker is a mission in The Lost Frontier. After successfully boarding the Phantom Blade, Jak confronted Captain Phoenix, quickly turning into a brawl. During the fight, Jak accidentally knocked the eco seeker out of Phoenix' hand, causing it to fall out of the window and into the Brink volcano below. Keira Hagai demanded a truce between the two until they got it back, and Phoenix and Jak thus raced each other for the artifact.
Before returning to Brink Island you will want to visit Keira's workshop and buy new eco skills from her. Then head for the hangar and use a plane to return to the island. You will land in front of the Castaway's treehouse, and from there the path to the volcano is marked by wooden signs. After going through a door you will have to use your eco construct power to reach the door to the next area atop a cliff. In the following area you will run into another Precursor idol, which gives you the eco rocket jump power to be used with, as all other powers, + (for PlayStation 2) or (for PlayStation Portable).
Use your new power on yellow eco vents and clouds to reach otherwise inaccessible heights. Once you have reached the cliff just ahead, you can open a chest for the Crash Plate Armor. Here you will run into Phoenix, who promptly runs off in chase of the eco seeker. Note that Phoenix is otherwise not seen inside the volcano itself. As you move through the volcano, jumping over platforms and swinging on poles, you must watch for cave-ins, unstable footing that collapses when you stand on it, and vents that periodically release fire.
Use the rocket jump along with your eco construct power to proceed through the area, defeating a new type of armadillo and the new drillbots as you advance. The former has a short-range fire breath attack and the latter wield long-rage blasters, and each can take more damage than their predecessors (the drillbots' being the sawbot).
As you move toward the top of the volcano you will have to make your way across increasingly difficult platforming and combat challenges, until you finally reach the eco seeker, after which you can return to the Hellcat and leave the island. Part way through your journey back to the Phantom Blade, the Castaway will make himself known as he had stowed away on your ship during the mission.