We consider the dynamic breakthrough of a large bubble which is trapped below a porous screen and exposed to a liquid flow. Due to gravity, the bubble is rather flat and blocks part of the screen. Upward liquid flow across the screen leads to a pressure difference between its front and back side. As this pressure difference exceeds the bubble point threshold, the trapped bubble starts to break through the screen causing a number of small bubbles to emerge in chains from the upper side. These emerging bubbles form and detach in their typical manner. They affect the breakthrough and even bring it to a halt as the pressure difference falls below a detachment pressure which is intrinsic to the screen pores. During breakthrough, the trapped bubble shrinks and correspondingly blocks the screen to a lesser extent. The liquid flow around the trapped bubble deforms it and tends to make it flatter. The interplay of all these effects is a complex issue that is addressed in the present article. We develop a model comprising most of the effects and present it along with original experimental data. (C) 2012 Elsevier Ltd. All rights reserved.