Module 073 · Landscape Intelligence
Not All Desert
Is Sand
Hammada, reg, erg, oued. Four Arabic words for four types of desert. Sand dunes are the minority landscape — rock, stone, and gravel cover 75% of the Sahara.
001 — The Four Types
Four Deserts
Erg
عرق
from Arabic "arq" — dune field
~25% of the Sahara. The part everyone imagines. The part that is the minority.
Two famous ergs: Erg Chebbi (near Merzouga) — 28km north-south × 5–7km east-west, dunes to 150–160m, ~200 km². Erg Chegaga (near M'Hamid) — 40km expanse, dunes to 120m, more remote and wild. Also: Erg Lihoudi, Tinfou Dunes. All are on the far western edge of the Sahara, along the Algerian border.
A vast area of wind-blown sand where dunes cover more than 20% of the surface. Technically, an erg must exceed 125 km² to qualify — smaller areas are "dune fields." Individual dunes in ergs exceed 500m in width or length. Sand depths range from centimetres (Selima Sand Sheet, Egypt) to 21–43m in the Sahara. Dunes are constantly migrating, reshaping, and burying. The sand itself is a geological product: wind sorts sediment, carrying away fine dust and silt, leaving heavier grains to accumulate in basins downwind of dry riverbeds, floodplains, and lake beds. 85% of all Earth's mobile sand is found in ergs exceeding 32,000 km². The largest erg on Earth is the Rub' al Khali (Empty Quarter) in Arabia.
~25% of the Sahara is sand. The erg is the minority landscape
002 — The Sand
Morocco's Ergs
Erg Chebbi
Near Merzouga, southeastern Morocco. ~40km from Erfoud, on the Algerian border
28km north-south × 5–7km east-west. ~200 km²
Max Height150–160m (some sources cite 300m for tallest peak)
Morocco's most famous dunes. Rose-gold to orange. Dramatic against flat grey hammada. Tourist infrastructure since 1980s. 70+ hotels in Merzouga. Camel treks, luxury camps, sandboarding. Legend: God sent the dunes as punishment for refusing a weary traveller
Paved road from Erfoud to Merzouga. 8–10hr drive from Marrakech or Fez. October–April best season. Summer: 45°C+
Erg Chegaga
Beyond M'Hamid el Ghizlane, end of paved road. Deep Sahara
40km expanse — larger footprint than Erg Chebbi
Max Height~120m — lower than Chebbi but broader
Wild, remote, less developed. No village lights, no morning roosters. 4×4 access only from M'Hamid (~60km off-road). The erg for those who want true desert silence. Eco-camps and bivouacs. Fewer tourists, bigger sky
Requires 4×4 from M'Hamid. 1.5–2hr off-road. Often combined with Drâa Valley route. Add 1–2 days vs Chebbi itinerary
Tinfou Dunes
Near Zagora, Drâa Valley
Small dune field — more a taster than a full erg
Max Height~15–20m
The gateway dunes for travellers coming from Ouarzazate. A brief taste of sand before the road continues to M'Hamid. Quick camel rides, sunset photos
Roadside, paved N9 between Zagora and M'Hamid. Easy stop
Desert Types — Mapped
Sahara in Numbers
9.2–9.4 million km² (~3.6M sq mi). Largest hot desert on Earth
Wikipedia / National Geographic
20–30% of surface is sand dunes and sand sheets. Sources vary: Britannica says 25%, Nat Geo says 20% (ergs), others 30%
Britannica / Nat Geo / IFLScience
Rocky hammada (stone plateaus) and reg (gravel plains) — 70–80% of surface
Wikipedia / IFLScience
10+ countries including Morocco, Algeria, Tunisia, Libya, Egypt, Mali, Niger, Chad, Sudan, Mauritania
National Geographic
Just 5,400–10,000 years ago: lakes, rivers, grasslands, forests. Desertification triggered by Earth's axial shift
Multiple geological studies
~90 major oases across the Sahara. Including Morocco's Tafilalet (among the largest in the world)
Conservation Institute
Record high: 58°C (136°F) in Libya. Winter nights can drop below freezing. 35°C+ daily swing
Various
Southeastern Morocco: Drâa-Tafilalet region. 88,836 km². The interface zone where Atlas meets Sahara
Moroccan census / DWL Module 079
004 — Chronology
From Green Sahara
to Sand Sea
The Green Sahara. Lakes, rivers, forests, grasslands cover what is now desert. Humans fish, farm, paint rock art
Earth's axial tilt shifts. Precipitation collapses. The Sahara desertifies rapidly — a geological catastrophe measured in centuries, not millennia
Sahara reaches approximately its current extent. Erg, reg, and hammada landscapes established. Trans-Saharan trade routes develop along oued valleys and oases
Sijilmassa flourishes at the edge of the erg, controlling trans-Saharan caravan routes. Gold, salt, and slaves flow through the reg
European exploration and colonial mapping of the Sahara. French introduce terms like "erg," "reg," and "hammada" to Western geographic vocabulary
Morocco's southeastern border with Algeria formalised. Erg Chebbi and Erg Chegaga fall on Morocco's side
Tourism arrives at Erg Chebbi. Merzouga develops from a small hamlet to a desert gateway town with hotels and camps
Rare flooding near Erg Chebbi destroys buildings and kills three — a reminder that "desert" does not mean "waterless"
Sahara expanding southward at ~48km/year (some estimates). Climate change + deforestation. Morocco's pre-Saharan steppe under pressure
Key Numbers
The fraction of the Sahara covered by sand dunes and sand sheets. The rest is hammada, reg, oued, salt flat, and mountain. The desert of imagination is the minority
Maximum dune height at Erg Chebbi — Morocco's tallest sand dunes. Rising from flat grey hammada like an orange cathedral
The expanse of Erg Chegaga — Morocco's largest erg. Broader than Chebbi but lower. Reachable only by 4×4 from M'Hamid
Length of the Oued Drâa — Morocco's longest river. It flows from the Atlas to (sometimes) the Atlantic, creating the oases that sustain life at the desert's edge
Years since the Green Sahara ended. The desert is geologically young. What is now hammada was once grassland. What is now erg was once lake bed
Major oases across the Sahara — the life-support systems of the desert. Morocco's Tafilalet oasis is among the largest in the world
Sources
Erg (landform), Hamada, Sahara. Geological definitions, coverage statistics, aeolian processes
Sahara Desert — sand sheets and dunes cover approximately 25% of surface
Ergs cover 20% of the Sahara. Algeria desert coverage. Sahara ecosystem descriptions
"The Sahara Desert Isn't As Sandy As You Think." 25% sand, 75% hammada and reg. Grand Erg Oriental at 308,210 km²
Erg Chebbi: "rose-gold dunes rise dramatically above pancake-flat, grey hamada." Shape-shifting over 28km
Erg, reg, hamada terrain types. Morocco-specific desert landscape descriptions and travel guidance