Is it possible to delete all tasks in a column?

By default, it’s not possible to delete all tasks from a column in one action. However, a Delete all function is available through the Developer Tools Power-Up.

To use it, go to Settings - Power-Ups, enable Developer Tools and add this link to the Developer Tools dialogue window:
/scripts/delete-all/delete-all.js
It will add a new context menu option, letting you Delete all tasks in any column:

We highly recommend that you archive tasks, rather than delete them, since archived tasks are still part of the process analysis, whereas deleted ones aren’t.