Over the past week millions of travelers have been stranded, both within Europe and abroad, due to a massive volcanic eruption. The glacier-covered Eyjafjallajokull volcano in Iceland has been spewing molten lava and toxic volcanic ash into the air with no end in sight.

The volcanic eruption in Iceland has wreaked havoc on international travel, grounding planes that might encounter the ash cloud during flight. Not only does smoke and ash reduce visibility, but microscopic particles could melt in the heat of the planes’ turbine engines, causing them to shut down.

While the primary focus of stranded passengers is likely where they will sleep until they can find a way home, at least some volcano refugees are questioning what effect their inability to leave the US will have on future US immigration status.

Visitors to the US, either on a visa or through the Visa Waiver Program (VWP), are typically given a deadline by which they must leave the US. This “authorized stay” expiration date is noted on the visitor’s I-94 card (I-94W for VWP visitors) and cannot usually be extended without prior application. So, what happens when a foreign national is unable to fly back to his or her home country because airlines have canceled air travel?

US Customs and Border Patrol (CBP), a division of the US Department of Homeland Security (DHS), has issued a Travel Advisory concerning the Icelandic volcano. If visitors to the US are stranded here because of airport closures in Europe arising from the Icelandic volcano, and are about to exceed their authorized stay because of it, they may be able to avoid incurring a penalty for staying past their period of authorized stay.

If the visitor entered via the VWP, and is at the airport but unable to depart timely, he or she should contact CBP at the airport or contact the US Citizenship and Immigration Services office (USCIS). If the visitor entered under a visa, he or she should contact the nearest USCIS office for information on how to extend the authorized stay.