Why the Arabian Gulf's Western Coastal Plain Is Wider Than the Eastern

The **western (Arabian) coastal plain** of the Persian/Arabian Gulf is significantly **wider** than the **eastern (Iranian) coastal plain**. Four geological factors explain this asymmetry:

1. Tectonic Setting:
   • **Arabian Plate (West):** Stable, subsiding passive margin. Broad, gentle slope.
   • **Iranian Plate (East):** Active collision with Eurasia (Zagros orogeny). **Zagros Mountains** thrust up *directly adjacent* to coast — narrow, steep, rugged coastal zone.
2. Sediment Supply:
   • **West:** **Tigris & Euphrates** (and Karun, historically) deliver **massive sediment loads** from Mesopotamian basin → build broad deltaic/alluvial plains (Kuwait, Saudi, Bahrain, UAE coasts).
   • **East:** **Arid Iranian interior** — few perennial rivers, low sediment yield. Limited alluvial input.
3. Quaternary Sea-Level Change:
   • **Last Glacial Maximum (~20 ka):** Sea level ~120 m lower. **Entire Gulf exposed** as flat, sediment-covered plain (Tigris-Euphrates flowed to Strait of Hormuz).
   • **Post-Glacial Transgression:** Rapid flooding. **Western side** received continued high sediment flux → **progradation (seaward build-out)** of coastal plain. **Eastern side** — steep mountain front → **drowned coastline**, minimal plain development.
4. Coastal Processes:
   • **West:** Higher wave energy (prevailing NW Shamal winds) → **longshore drift, barrier islands, sabkhas (salt flats), lagoons** — expands plain width.
   • **East:** Lower wave energy (fetch limited by Qatar/UAE), steeper nearshore → narrow beaches, rocky shores.

**Result:** A wide, sediment-rich, low-gradient Arabian shelf vs. a narrow, tectonically steep, sediment-starved Iranian margin. The Gulf's geometry is a textbook **asymmetric rift basin**.