The Strait of Hormuz is, geologically speaking, an accident.
It formed roughly five million years ago when tectonic shifts cracked open a narrow passage between the Arabian Peninsula and what is now Iran. The crack is so narrow that at its tightest point, the usable shipping lanes, two lanes in, two lanes out, measure just two miles wide each. A moderately sized American city could straddle the entire passage.
That accident of geology now controls a remarkable share of the world's energy. According to the U.S. Energy Information Administration, about 20 percent of the world's petroleum supply passes through the strait daily, roughly 20 million barrels. There is no practical alternative route. Pipelines exist but cannot absorb anything close to that volume.
What makes the strait so difficult to protect is the same thing that makes it so valuable: its narrowness. Iran controls the entire northern coastline and the majority of the islands dotting the passage. Ships navigating the lanes are well within range of shore-based missiles, mines, and fast-attack boats.
Naval mines in the strait are programmable, set to respond to specific acoustic or magnetic signatures, meaning they can be selectively triggered.
The strait's geology is strange even beyond its narrowness. The Musandam Peninsula, which juts northward from Oman, is a showcase of folded, upthrust rock called ophiolite, ancient ocean floor shoved onto land during a continental collision 60 to 95 million years ago. Geologists consider it the finest exposed ophiolite complex on Earth. Its black limestone cliffs rise 800 meters straight out of the sea in fjord-like inlets that have earned the region the nickname "the Norway of Arabia."
The surrounding waters host some of the most heat-tolerant coral reefs on the planet, thriving in temperatures that would kill most tropical corals.