Google’s Daniel Waisberg did this outstanding post and illustration, he calls sketches, of how Google would categorize the types or causes of organic traffic drops. The categories include technical issues on the site level, technical issues on the page level, manual actions, algorithmic changes, seasonality and simple reporting bugs.

Here are the sketches that show manual actions and site wide technical issues generally lead to massive and rapid traffic drops whereas page level technical issues and algorithmic changes lead to slower paced drop offs. Here is the graphic:

Daniel wrote “there are five main causes for drops in Search traffic” and listed these five:

Technical issues: Errors that can prevent Google from crawling, indexing, or serving your pages to users – for example server availability, robots.txt fetching, page not found, and others. Note that the issues can be site-wide (for example, your website is down) or page-wide (for example, a misplaced noindex tag, which would depend on Google crawling the page, meaning there would be a slower drop in traffic).
Security issues: If your site is affected by a security threat, Google may alert users before they reach your site with warnings or interstitial pages, which may decrease Search traffic.
Manual Actions: If your site does not comply with Google’s guidelines, some of your pages or the entire site may be omitted from Google Search results through a Manual Action.
Algorithmic changes: Google is always improving how it assesses content and updating its algorithm accordingly; core updates and other smaller updates may change how some pages perform in Google Search results. To keep track of future updates, subscribe to our Google Search News YouTube series or follow us on Twitter.
Search interest disruption: Sometimes changes in user behavior will change the demand for certain queries, either as a result of a new trend, or seasonality throughout the year. This means your traffic may drop simply as a result of external influences.

The post goes on to explain how to do this analysis, so I recommend reading it.

It is super cool that Google shared what these traffic drops generally look like by cause.

Of course, then we had some funny responses:

Forum discussion at Twitter.

Update: Google in March 2023, made a video around this: