Blogger Skyrocket visit phenomenon

I have a blogger using the google platform and most of the content is made of not original content and I have this blog for around 3 years and points to a custom domain that I bought and very often this phenomenon happens one day I have 170 to 300 visits and sometimes 1 time per week or one time every 2 weeks I have 6k to 15k visitors all coming from google in one day, below the screenshot of analytics, why this happen? google dance? anyway that is something that makes more good than harm