Geology of Uttarakhand :

Geology Himalaya is the product of ongoing convergence and ultimate collision of Indian and Eurasian tectonic plates and the same is responsible for both, picturesque landscape as also physiography of the terrain and its fragility and disaster vulnerability. Plains in the southern portion of the state falls under Indo – Gangetic alluvium and from south to north this is divided into areas designated as Terai and Bhabhar. The former has shallow water table while the water table in the latter is relatively deep. Siwaliks that consist of sedimentary rocks are thrust over the Indo – Gangetic alluvium along northeasterly dipping Himalayan Frontal Fault (HFF).

Siwaliks or Outer Himalayas in the state are largely covered by dense forest, mostly of sal. Wide intermontane valleys, known as duns, are developed in the Siwaliks. Dehradun, the state capital, is located in one such valley. It is in close proximity of both HFF that is noticed near Mohand and Main Boundary Thrust (MBT) that is located near Sahanshahi Ashram. Both these tectonic boundaries show NE – SW trend. Siwaliks are thrust over by Lesser Himalayas that consist of low grade metamorphic rocks, along the MBT. To the north Main Central Thrust (MCT) represented by as many as three interrelated tectonic discontinuities brings high grade metamorphic rocks of Central Crystallines in juxtaposition with the rocks of Lesser Himalaya. MCT zone is considered to be the tectonically active and fragile. Most disasters in the state fall in this zone. At the northern extremity of the state Tethyan Thrust brings relatively young sedimentary rocks of Tethyan Group in juxtaposition with the Central 20 Crystalline rocks. This area is largely snow bound and does not have many habitations. Geological setup of the state.

Geo – tectonic set up of the region together with its evolutionary history, geomorphology and meteorological characteristics make Uttarakhand prone to a number of natural hazards. Besides earthquakes the area is frequently devastated by landslides, cloudbursts, flash floods, floods, avalanches, droughts, lightening, cold waves and hailstorms.

Due to the ongoing tectonic movements the region has accumulated enormous strain that makes it susceptible to seismic tremors. The state falls in either Zone IV or Zone V of Earthquake Zonation Map of India. Pithoragarh, Bageshwar, Chamoli and Rudraprayag districts together with some areas of Almora, Champawat, Tehri, Uttarkashi and Pauri district fall in Zone V while Udhamsingh Nagar, Nainital, Haridwar and Dehradun districts fall fully in Zone IV. In the past the State has witnessed two major earthquakes (Uttarkashi 1991 and Chamoli 1999). Losses incurred in these earthquakes.
The state however falls in Seismic Gap of 1905 Kangara Earthquake and 1934 Bihar – Nepal Earthquake. Non-occurrence of great earthquake (Magnitude > 8 on Richter Scale) for more than 200 years further enhances seismic risk in the region. Geo-tectonic history of the terrain makes the state highly prone to landslides. Every year, the state faces massive losses, particularly during the monsoon season, due to rain, landslide, cloudburst, flood, water logging and flash flood events. These cause disruption of transport infrastructure, water supply, telecommunication and result in loss of other private and public infrastructure. Small and marginal farmers of the hills loose substantial portion of their agricultural produce and sometimes lose agricultural lands permanently due to these events.

In the year 2013 the monsoon was early to arrive and interaction of the same with the Westerlies resulted in heavy precipitation in the region. This caused massive devastation in the state on 16 and 17 June, 2013. More than 4,000 persons went missing in these incidences that caused massive loss of infrastructure and property.

Climate and Weather :

Except for a small area falling in the plains the state experiences cold winters with higher reaches experiencing snowfall during winters, appreciably good rainfall during monsoons, and mild summers. The climate coupled with scenic beauty attract tourists in large numbers from across the world. State is bestowed with a relatively high average annual rainfall of 1,229 mm. Normally, rains start in late April and continue upto September. The intensity of rainfall however increases between June and September. Extreme rainfall events are however becoming more and more frequent and in 2010, 2012 and 2013 many parts of the state experienced exceptionally high rainfall events and the same are often attributed to climate change. During the summers temperatures, mainly in the plains and river valleys often crosses the 40° C mark. Winters however are very cold with average temperatures going below 5° C. The lowest recorded temperature ranges between 5° to - 7°C while the highest ranges between 40 to 45° C.