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How did the sinking of the Deepwater Horizon rig lead to oil leaking into the Gulf of Mexico?

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Fireboats battle a blaze on the Deepwater Horizon drilling rig in the Gulf of Mexico, April 2010. — Deepwater Horizon oil spill Fireboat response crews attempt to extinguish the blaze aboard the Deepwater Horizon oil rig in the Gulf of Mexico, April 21, 2010.

The Deepwater Horizon oil spill was triggered by a surge of natural gas that blasted through a concrete core, which had been installed to seal an oil well for future use. This gas traveled up the rig's riser to the platform, where it ignited, causing an explosion that killed 11 workers and injured 17.12

The rig subsequently capsized and sank on April 22, 2010. This sinking ruptured the riser, which had previously been used to inject drilling mud into the well to counteract the upward pressure of oil and gas. With the riser broken and no opposing force to hold back the contents of the well, oil began to discharge directly into the Gulf of Mexico. Although the rig was equipped with a blowout preventer designed to seal the well in such emergencies, the device malfunctioned because the pipe had bent under the intense pressure of the rising gas and oil, preventing the fail-safe mechanism from closing the channel.324