If they're stack dumps, then they're written out when SQL encounters fatal errors (like invalid memory addresses) or some forms of severe corruption. Either way, repeated stack dumps suggest something is seriously wrong.
If they are dumps, there will be files .mdmp and .txt at least with the same name. Also there will be messages in the error log stating that SQL stack dumped.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability