It is important to focus on specifics when you are searching for information.
Which of the following questions would give you the most focused set of results?
What is a volcanic eruption?
How long do volcanic eruptions last?
Does the Icelandic government hold any record of the duration of volcanic eruptions in Iceland?
What research has been conducted using the records of the duration of volcanic eruptions in Iceland?
The correct answer is d.
Usually the more detailed your question (the more concepts it contains), the better. But this is not always crucial, depending on the context of the search.
It is also good to focus your question, making it as specific as possible e.g. by specifying a geographic location and a time period.