Iran occupies 1,648,195 square kilometers in southwestern Asia, making it the seventeenth largest country on Earth. The nation shares land borders with seven countries: Turkey and Iraq to the west, Armenia and Azerbaijan to the northwest, Turkmenistan to the northeast, and Afghanistan and Pakistan to the east. The northern frontier follows 740 kilometers of Caspian Sea coastline, while the southern boundaries extend along 2,440 kilometers of Persian Gulf and Gulf of Oman shoreline. The Strait of Hormuz, a waterway twenty-one nautical miles wide at its narrowest point, separates Iranian territory from the Arabian Peninsula and channels approximately thirty percent of global seaborne oil traffic.
The Persian Plateau forms the geological foundation of Iran, a raised landmass averaging 1,200 meters above sea level that tilts from northwest to southeast. This plateau resulted from the collision between the Arabian and Eurasian tectonic plates, a process that began approximately thirty million years ago and continues to produce measurable seismic activity. The same tectonic forces created Iran's two dominant mountain ranges. The Zagros Mountains extend 1,500 kilometers from the northwest border with Turkey to the Strait of Hormuz, forming a barrier between the plateau interior and the lowlands of Mesopotamia. The Alborz Mountains stretch 900 kilometers along the southern Caspian coast, rising abruptly from sea level to peaks exceeding 4,000 meters within horizontal distances of less than fifty kilometers in some locations.
Mount Damavand, a dormant stratovolcano in the central Alborz range, reaches 5,610 meters elevation, making it the highest point in Iran and the highest volcano in Asia. The mountain last erupted approximately 5,300 years ago based on radiometric dating of lava flows. Fumaroles near the summit continue to emit sulfurous gases, indicating ongoing geothermal activity beneath the edifice. The peak remains visible from Tehran, located sixty-six kilometers southwest, on days when atmospheric conditions permit.
The interior basins of the Persian Plateau contain two major desert systems that together cover approximately 200,000 square kilometers. Dasht-e Kavir, the Great Salt Desert, extends across the north-central plateau between the Alborz and Zagros ranges. The surface consists of salt crusts, mud flats, and kavirs—treacherous wetlands where groundwater saturates thick clay deposits, creating surfaces that appear solid but cannot support weight. Surface temperatures in Dasht-e Kavir exceed 50 degrees Celsius during summer months. Dasht-e Lut occupies the southeastern plateau, reaching into Kerman and Sistan-Baluchestan provinces. A 2005 NASA satellite measurement recorded a land surface temperature of 70.7 degrees Celsius in Dasht-e Lut, the highest ground temperature ever measured on Earth by satellite. The Gandom Beryan plateau within Dasht-e Lut supports no vegetation or microbial life in its most extreme zones due to sustained surface temperatures exceeding 60 degrees Celsius.
Iranian rivers originate in the mountain ranges and flow toward interior basins or external seas. The Karun River, originating in the Zagros Mountains near Zard-Kuh peak, flows 950 kilometers through Khuzestan Province to the Persian Gulf. The Karun is the only navigable river in Iran, supporting commercial traffic for approximately 180 kilometers upstream from its delta. Historical records indicate the Karun carried Persian Gulf shipping to Shushtar until siltation and political changes ended navigation above Ahvaz in the twentieth century. Other significant rivers include the Karkheh, which flows 900 kilometers through western Iran, and the Zayandeh River, which irrigates the Isfahan oasis before terminating in the Gavkhouni marsh, an endorheic wetland that receives water during wet seasons only.
Lake Urmia in northwestern Iran was historically the largest lake in the Middle East, with surface area measurements of 5,200 square kilometers recorded in the 1990s. The hypersaline lake, with salinity levels reaching 340 grams per liter, supported unique brine shrimp populations and served as critical habitat for migratory birds including flamingos, pelicans, and egrets. Documented declines in inflow from the Zarineh River and increased water extraction for agriculture reduced Lake Urmia's surface area to approximately 1,000 square kilometers by 2015. Satellite imagery from the European Space Agency confirmed partial recovery to approximately 2,500 square kilometers by 2020 following government-mandated reductions in agricultural water use. The lake contains more than one hundred small islands, including Shahi Island and Kaboudan Island, both of which expanded in area as water levels declined.
The Caspian Sea coastline in northern Iran represents a distinct geographical zone separated from the interior plateau by the Alborz mountain wall. The Caspian shore sits twenty-seven meters below global sea level, making it the lowest elevation in Iran and creating a precipitation trap where moist air masses rising from the water surface encounter the Alborz barrier. This collision produces annual precipitation exceeding 1,500 millimeters in western Caspian provinces, compared to national averages below 250 millimeters. The coastal strip supports the Hyrcanian Forests, a temperate deciduous woodland that has existed continuously for twenty-five to fifty million years according to paleobotanical evidence. These forests contain relict species including Caucasian leopards, Persian fallow deer, and European bison populations that disappeared from surrounding regions during glacial periods.
Iran's southern coastline along the Persian Gulf and Gulf of Oman exhibits different characteristics than the Caspian shore. The waters remain shallow across extensive areas, with average depths of thirty-five meters in the Persian Gulf and occasional depths below ten meters extending thirty kilometers offshore. These shallow waters support coral reef ecosystems, mangrove forests, and seagrass meadows that provide habitat for dugongs, hawksbill turtles, and commercial fish species. Summer water temperatures in the Persian Gulf exceed 35 degrees Celsius, approaching the upper thermal tolerance limits for coral species. Qeshm Island, the largest island in the Persian Gulf at 1,491 square kilometers, sits in the Strait of Hormuz and contains geological formations including the Stars Valley canyon system, Namakdan salt dome, and Chahkooh canyon. UNESCO designated Qeshm as a Global Geopark in 2006, recognizing geological features that record 540 million years of Earth history. Kish Island, located in the central Persian Gulf approximately eighteen kilometers from the mainland, covers 91.5 square kilometers and functions as a free trade zone attracting domestic tourism and international commerce.
Hormuz Island near the Strait of Hormuz displays unusual geology that creates multicolored soil deposits ranging from red and yellow to purple and white. These colors result from iron oxide, sulfur, and other mineral concentrations in volcanic and sedimentary rock layers exposed by erosion. The island has supplied red ochre pigment for regional trade since pre-Islamic times. Local production continues, with residents collecting and processing the colored earth for sale as natural dye.
Iran's climate varies dramatically across different regions due to latitude, elevation, and proximity to water bodies. The country spans latitudes from approximately 25 degrees north near the Gulf of Oman to 40 degrees north at the Azerbaijan border, a range that encompasses subtropical and temperate climate zones. Tehran, at 1,200 meters elevation, records average January temperatures of 2 degrees Celsius and July averages of 30 degrees Celsius, with annual precipitation near 230 millimeters concentrated in winter and spring months. The capital experiences approximately 120 clear days, 140 partly cloudy days, and 105 overcast days per year based on meteorological records from Mehrabad Airport.
The Caspian coastal provinces of Gilan and Mazandaran receive substantially different weather than locations south of the Alborz range. Rasht, the capital of Gilan Province, records average annual precipitation of 1,355 millimeters, with monthly totals sometimes exceeding 200 millimeters during autumn. The Caspian coast maintains relatively mild winter temperatures, with January averages near 8 degrees Celsius in Rasht, while summer temperatures remain moderate due to proximity to the water mass. This climate supports rice cultivation across the coastal plain, making Gilan and Mazandaran the primary rice-producing regions in Iran.