At least 100 dead, massive destruction and more than 200,000 homeless: What we know now about Tuesday's Beirut blast. Residents of Beirut are surveying the damage Wednesday after a massive explosion rocked the Lebanese capital. The cause of the explosion has yet to be officially determined, but officials said it may have been caused by ammonium nitrate, a highly explosive material that was stored at the port. Ref. USAToday.