Michael Dahl 
Prisoners of the Poison Sea [PDF ebook] 

After a recent daring escape attempt, Zak Nine and his Quom friend Erro are imprisoned in the most inescapable region of Alcatraz. The boys are locked in separate cages, hovering at the end of unbreakable chains over a boiling sea of poison. How will the boys escape their latest dilemma? Even if they break out of their cells, how will they travel across the venomous waters to safety? It’s the most perilous adventure yet as the boys try to escape from Planet Alcatraz.