Some of my favorites in the famous disasters genre, not necessarily ebooks:
1)
And the band played on by Randy Shiltz. I remember when I read that I couldn't put it down -- stayed up for two or three days in a row! (The beginnings of the AIDS epidemic.)
2) One of the early Galveston hurricane books was great -- I can't remember which one, but on this list
(
http://earlytexashistory.com/Pomeros...galvbooks.html)
many were written before 1910 so may be public domain and thus available as ebooks
3)
A night to remember Walter Lord, 1955. Not public domain yet, but a really good one about the Titanic.
4)
Alive! The story of the Andes survivors Piers Paul Read, 1974. A little gory, but gripping.
5)
History of the Donner party by C.F. McGlashan (late 1800's) is available at PG