People are seen at the sulfur fountain, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

General view of east of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

General view of the bridges and the Old city of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

People sit in water after being covered with mud, which helps to treat the skin diseases, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid TPX IMAGES OF THE DAY

People sit in water after being covered with sulfur, which helps to treat the skin diseases, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

General view of Bashtabiya castle, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

A man washes himself after being covered with mud, which helps to treat the skin diseases in Hammam Al-Alil south of Mosul, Iraq August 21, 2019. Picture taken August 21, 2019. REUTERS/Abdullah Rashid

A view of the rocks near the sulfur fountain on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

General view of Al-Shifa Quarter in the Old city of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

A boy pours water at a man who has been covered with mud, which help to treat the skin diseases, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

A man covers himself with mud, which helps to treat the skin diseases, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

People sit inside the sulfur fountain, which helps to treat the skin diseases, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

People sit in water at the sulfur fountain on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

A man and his son cover themselves with mud, which helps to treat the skin diseases, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

People walk toward the old castle of Bashtabia, after they finish swimming in the sulfur fountain, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

People are seen at the sulfur fountain, on banks of Tigris river west of Mosul, Iraq August 20, 2019. Picture taken August 20, 2019. REUTERS/Abdullah Rashid

A view shows packs with granulated sulfur at the Achinsk refinery, which was acquired by Rosneft company in 2007 and currently processes West Siberian crude delivered via the Transneft pipeline system, in Krasnoyarsk Region, Russia July 23, 2018. Picture taken July 23, 2018. REUTERS/Ilya Naymushin

An employee demonstrates granulated sulfur at the Achinsk refinery, which was acquired by Rosneft company in 2007 and currently processes West Siberian crude delivered via the Transneft pipeline system, in Krasnoyarsk Region, Russia July 23, 2018. Picture taken July 23, 2018. REUTERS/Ilya Naymushin

Major Jeff Hickman, of the Hawaii National Guard, measures sulfur dioxide gas levels at a lava flow near Pahoa during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., June 3, 2018. REUTERS/Terray Sylvester

Soldiers of the Hawaii National Guard measure sulfur dioxide gas levels near a lava flow in Leilani Estates during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., June 3, 2018. REUTERS/Terray Sylvester

Soldiers from the Hawaii National Guard monitor sulfur dioxide gas levels near a lava flow in Leilani Estates during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., June 3, 2018. REUTERS/Terray Sylvester TPX IMAGES OF THE DAY

Soldiers from the Hawaii National Guard monitor sulfur dioxide gas levels near a lava flow in Leilani Estates during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., June 3, 2018. REUTERS/Terray Sylvester TPX IMAGES OF THE DAY

Sgt. Gavin Ching of the Hawaii National Guard monitors sulfur dioxide gas levels near a lava flow on Highway 132 in Pahoa during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., June 3, 2018. REUTERS/Terray Sylvester

Soldiers from the Hawaii National Guard monitor sulfur dioxide gas levels near a lava flow in Leilani Estates during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., June 3, 2018. REUTERS/Terray Sylvester

Sgt. Gavin Ching (R) of the Hawaii National Guard monitors sulfur dioxide gas levels in Leilani Estates during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., June 3, 2018. REUTERS/Terray Sylvester

Leilani Estates resident Karin Tihopu stands inside her "safe room," or closet she has made air tight, at her home near Pahoa, Hawaii, U.S., May 27, 2018. Many Leilani Estate residents who were not affected directly by the lava eruptions are under constant threat by volcanic gases. Rather than evacuate, many like Tihopu, choose to remain in their homes but have created areas to escape if sulfuric gas levels become hazardous. REUTERS/Marco Garcia

Lieutenant Colonel Charles Anthony, of the Hawaii National Guard, measures sulfur dioxide gas levels at a lava flow on Highway 137 southeast of Pahoa during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 20, 2018. REUTERS/Terray Sylvester TPX IMAGES OF THE DAY

Lieutenant Colonel Charles Anthony, of the Hawaii National Guard, measures sulfur dioxide gas levels at a lava flow on Highway 137 southeast of Pahoa during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 20, 2018. REUTERS/Terray Sylvester TPX IMAGES OF THE DAY

Lieutenant Colonel Charles Anthony, of the Hawaii National Guard, measures sulfur dioxide gas levels at a lava flow on Highway 137 southeast of Pahoa during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 20, 2018. REUTERS/Terray Sylvester

Lieutenant Colonel Charles Anthony, of the Hawaii National Guard, measures sulfur dioxide gas levels at a lava flow on Highway 137 southeast of Pahoa during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 20, 2018. REUTERS/Terray Sylvester

Lieutenant Colonel Charles Anthony, of the Hawaii National Guard, measures sulfur dioxide gas levels at a lava flow on Highway 137 southeast of Pahoa during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 20, 2018. REUTERS/Terray Sylvester

Lieutenant Colonel Charles Anthony, of the Hawaii National Guard, measures sulfur dioxide gas levels at a lava flow on Highway 137 southeast of Pahoa during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 20, 2018. REUTERS/Terray Sylvester

Lieutenant Colonel Charles Anthony of the Hawaii National Guard monitors sulfur dioxide gas levels in Leilani Estates during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 18, 2018. REUTERS/Terray Sylvester

Lieutenant Colonel Charles Anthony of the Hawaii National Guard monitors sulfur dioxide gas levels in Leilani Estates during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 18, 2018. REUTERS/Terray Sylvester

Senior airmen Orlando Corpuz, (L), and John Linzmeier, of the Hawaii National Guard, monitor sulfur dioxide gas levels in Leilani Estates during ongoing eruptions of the Kilauea Volcano in Hawaii, U.S., May 18, 2018. REUTERS/Terray Sylvester

Residents of the Leilani Estates subdivision drive through steam and sulfur dioxide gas near their homes during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Leilani Estates resident Delance Weigel, 71, walks toward steam and sulfur dioxide gas emerging from a crack in the ground near his home during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Lieutenant Aaron Hew Lew, of the Hawaii National Guard, measures levels of toxic sulfur dioxide gas near a lava flow in the Leilani Estates subdivision during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Lieutenant Aaron Hew Lew, (L), of the Hawaii National Guard, measures levels of toxic sulfur dioxide gas near a lava flow in the Leilani Estates subdivision during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Lieutenant Aaron Hew Lew, of the Hawaii National Guard, measures levels of toxic sulfur dioxide gas near a lava flow in the Leilani Estates subdivision during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Lieutenant Aaron Hew Lew, of the Hawaii National Guard, measures levels of toxic sulfur dioxide gas in the Leilani Estates subdivision during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Lieutenant Aaron Hew Lew, of the Hawaii National Guard, measures levels of toxic sulfur dioxide gas near a lava flow in the Leilani Estates subdivision during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Lieutenant Aaron Hew Lew, of the Hawaii National Guard, measures levels of toxic sulfur dioxide gas near a lava flow in the Leilani Estates subdivision during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Lieutenant Aaron Hew Lew, of the Hawaii National Guard, measures levels of toxic sulfur dioxide gas near a lava flow in the Leilani Estates subdivision during ongoing eruptions of the Kilauea Volcano, Hawaii, U.S., May 8, 2018. REUTERS/Terray Sylvester

Candida Duplessis, age 66 of Port Sulfur, sits with family members at the hurricane shelter set up in the Belle Chasse High School gym in Belle Chasse, Louisiana, U.S. October 7, 2017. Photo taken October 7, 2017. REUTERS/Jessica Resnick-Ault

Candida Duplessis, age 66 of Port Sulfur, sits with family members at the hurricane shelter set up in the Belle Chasse High School gym in Belle Chasse, Louisiana, U.S. October 7, 2017. Photo taken October 7, 2017. REUTERS/Jessica Resnick-Ault

An Iraqi boy bathes in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

An Iraqi man bathes in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

An Iraqi boy bathes in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

Iraqis bathe in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

Iraqis bathe in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

An Iraqi boy bathes in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

Iraqis bathe in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

Iraqis bathe in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

An Iraqi man bathes at a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

Iraqis bathe in a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

An Iraqi cover his boy with sand from a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem TPX IMAGES OF THE DAY

An Iraqi cover his boy with sand from a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem

An Iraqi cover his hand with sand from a sulfur pond at Hammam al-Alil city south of Mosul, Iraq April 3, 2017. Picture taken April 3, 2017. REUTERS/Suhaib Salem