The metreon cascade was a weapon of mass destruction designed by Dr. Ma'Bor Jetrel of the Haakonian Order. It used unstable metreon isotopes to create a devastating explosion, apparently similar to that of a nuclear weapon. The resulting radiation poisoning killed those who were not destroyed by the initial blast. Sufficient exposure to metreons resulted in the deadly disease metremia.
The metreon cascade was only used once, on the Talaxian moon of Rinax in 2356, ultimately concluding the Talaxian-Haakonian War, killing over 300,000 colonists. (VOY: "Jetrel", "Friendship One", "Homestead")