In order for volcano damage to be covered by homeowners insurance, eruptions would have to be listed as a “named peril” on the policy. Or alternatively, there would have to be an “open peril” policy without any exclusion for volcano eruptions.
Generally speaking, homeowners insurance rarely addresses volcano eruptions overtly. But while eruptions may not be included in a policy, some related events like fire and fallen objects may be explicitly covered. This provides some indirect protetction from volcanoes.
For more information on this topic, check out this article: Does Homeowner’s Insurance Cover Volcanic Eruptions?.