1. Cloudburst - At least 100 mm of rain in one hour over a 10x10 km area: This pair is correctly matched. The Indian Meteorological Department (IMD) defines a cloudburst as a sudden, intense rainfall event with at least 100 mm of rain falling within an hour over a small area, typically 10x10 km.
2. Glacial Lake Outburst Flood (GLOF) - Caused by melting snow and ice at high altitudes: This pair is incorrectly matched. While GLOFs are associated with glacial lakes, they are not directly caused by melting snow and ice. Instead, they typically occur when the moraine (natural dam) containing a glacial lake fails, often due to additional water from heavy rains, rapid snowmelt, or an ice avalanche.
3. Landslide - Triggered by tectonic activity alone: This pair is incorrectly matched. While tectonic activity can trigger landslides, they are more commonly initiated by heavy rains, earthquakes, volcanic activity, or human activities like deforestation and construction on slopes.
4. Flash Floods - Can occur even with moderate rainfall in fragile terrains: This pair is correctly matched. In ecologically sensitive and geologically fragile terrains like the Himalayas, even moderate rainfall can lead to flash floods due to saturated soils, steep slopes, and eroding land surfaces.
Only pairs 1 and 4 are correctly matched, making Option B: Only two pairs the correct answer.