A tsunami story with a happy ending? Read Terry Pratchett's The Nation

If you've not yet had your fill of tsunamis get the YA novel Nation by Terry Pratchett.
Its not really a story about tsunamis. Pratchett tells a tale of a British girl shipwrecked by a tsunami in the South Seas. A boy native to another island is also transplanted, via the same tsunami that destr

oyed his tribe (the Nation), to the same island the girl is stranded on. The girl, boy, and natives on this island adapt to the influx of refugees and raiders and rebuild their civilization.
Lots of the typical Pratchett humour and adventure in this non-Discworld novel where our teen protagonists "grow up" learn about leadership and responsibility and the nature of humanity. Pratchett's deft exploration of the nature of culture and religion is wrapped in an entertaining and witty story.