Safari used 70 GB of RAM
There are a number of things you can try...


Sometimes applications have memory leaks where the memory bloats over time, if you've been using Safari heavily, or using it for a long time without exiting and rebooting this could be an issue. Quitting Safari and reopening should fix this.
Check for extensions, and plugins that Safari uses to see if there are any malicious or unexpected plugins/try removing them temporarily to see if this fixes the issue.


Details of the Plug-Ins folders: https://support.apple.com/kb/PH19241?locale=en_GB&amp;viewlocale=en_US

Best to do a backup before tinkering in the Library folders!


Try creating a new user account and see if Safari has the same issue in this account.