Either that of a burst from the sun directly to earth - as has happened before, knocking out what electrical technology we had at the time - like telegraph transformers - could be tantamount to the burning of the Constantinople Library.
That set civilization - sciences, medicine, etc., - back hundreds of years.
I tell my kids and grandkids: PRINT OUT YOUR BEST PHOTOS and get them safely into albums. Print out email letters you don't want to lose forever and, also, WRITE REAL LETTERS.
I have photos that are are over 100 years old of family.
I have bundles of letters from my dear late grandparents - from the 30’s-40’s, and from my late parents. They are are wealth of family history. (Indeed, I have a book written by one of my 7th great great grandfathers in the 1600’s. (Gov. Wm. Bradford of the Mayflower. He wrote a journal for the family about the 20 years of struggle before, during and after the crossing to Plymouth. It was hunted down and printed in the late 1800’s. I have that edition as well as the one that has been continually reprinted for the past 60 years. Had that not been first in his pen on paper and then printed, it would have long been lost, along with all the history. Nearly everything we know about the Pilgrims is from this original family journal.)
In the last 10 years, we have gone from VCR’s to floppys to CD’s to DVD’s and those are already changing in size. It won't be long before whatever is on them will be trapped - as machines for playing them will change and become obsolete.
The written letter, the printed photo and the printed book will not become obsolete by ‘disappearing.’
Good grief, I'm glad I have an extensive collection of books...but now I'm thinking I need to start collecting libraries for my kids and grandkids.
Insanity.
We already had a problem assembling the technology to read NASA tapes from the Apollo era.