One of the main geological features of Ecuador is the north-south directed mountain range. This mountain range forms the division of the main land in three overall areas. The three areas are the coastal area in the west, the Amazonian area in the east and the mountainous (Andean) area in the middle. This mountain range is induced by the subduction of the Nazca plate under the South American plate. The Nazca plate is moved forward by magma streams in the astenosphere of the earth under the lighter continental South American plate. The subduction of the Nazca plate under the continental plate causes melt which rises and causes volcanism. Strong shear stresses occur where the plates converge and result in faults. This process started 60 million years ago in the alpine /cascadic orogenesis and is still active.
The hydrological pattern, visible in the illustration of the digital terrain model (reference), surmises different parent material in the southern part of the park from the northern part. No literature has been found to confirm, and no field checks have been done to verify this assumption. The geological map (IGM, mapa geologico del ecuador, 1976) does not mention another parent material in the specific region. It does mention a different type of parent material in the centre of the park.
The area consists of rocks belonging to the Tarqui formation (IGM, mapa geologico del ecuador, 1976) in places covered by tillite (a former till that has become compacted and lithified to form a tough sedimentary rock). The tillite is found around the depressions (the famous lakes of Cajas or swamps) and formed in the last ice age. The Tarqui formation (more than eighty percent of the parks area) consists of all kinds of parent material and can roughly be divided in three stratified units (stratums). A dark, fine-grained andesitic layer overlaid with a sequence of tuff of a ryolitic to dacitic composition. The uppermost layer consists of a homogeneous ryolitic medium grained material that appears in the upper part in the park and form well visible hills. The majority of the rocks show alteration, which is a result of hydrothermal processes (IGM, mapa geologico del Ecuador, 1976). In this research no special focus has been put on the parent material positioned below the volcanic ash layer.
After the last ice age the area has been covered by an astonishing equal spread ash layer. Origin of the ashes is presumably of the Sangay or the Tungurahua. These volcanoes, respectively 110 and 130 kilometres northeast from Cajas N.P. erupted some 3000 years ago according to Pascal Podowjesk (personal communications). This distance explains that the ashes are relatively homogenised in composition and depth for the whole of Cajas. The most important recent eruption of the Tungurahua has been in 1916 and the volcano has an eruption interval of about hundred years. Sangay is constantly active.
In the quaternary (Pleistocene), during the last ice age, there have been several glacial (and interglacial) periods. Those periods are perfectly corresponding with the European glaciations (Winckell, 1997). The most recent glacial extensions of Ecuador can be divided three groups. The oldest of the last three has an age of 13.000 to 16.000 years. The second and third originated respectively between 10.000 and 12.000 and 900 and 4.000 years B.P.
The soils in Cajas are all formed in volcanic ashes. The classification of the soils depends upon the method used, and in case of the FAO soil classification (World Reference Base for Soil Resources, 1998) of the organic material content. As the organic carbon content of some of the soils in Cajas is very high and the soil locally very shallow some soils are classified as Histosols and the ones with a lower organic carbon content (or deeper soil) as Andosols. Andosols can be defined as young soils formed in volcanic deposits. Diagnostic (andic) properties (WRB, 1998) are a dry bulk density of 0.9 kg dm3 or less, 10 percent or more clay and an Alox + 1/2Feox6 value in the fine earth fraction of 2 percent or more; and 6Alox and Feox are acid oxalate extractable aluminium and iron, respectively. A phosphate retention of 70 percent or more; and volcanic glass content in the fine earth fraction of less than 10 percent; and thickness of at least 30 cm.
The vegetation in the research area consists of grasses, evergreen herbs and some scattered dwarf forests. Páramo is the name for this high Andean grassland vegetation. Páramo means literally in Spanish wilderness or badlands, figurative it means solitarily area. It extends from western Venezuela to northern Peru at altitudes of 3000 to 4200m. (Archibold, 1995). Páramo vegetation has been described in detail by many authors like Cleef (1981) and Balslev and Luteyn (1992). The grassy Páramo cover mainly compromises of species like Calamagrostis, Festuca and Stipa but numerous herbs and small shrubs are intermingled with the grasses. The main ecological conditions of the Páramo influencing plants are:
Plant life has been adapted to these, extreme, ecological conditions. The most striking form of plant life in Cajas N.P. is the Puya (Puya sp.). Another striking and well-known plant species in the Páramo is the Frailejon (Espeletia sp), a giant stem rosette. The frailejon is locally present in the Páramo, but not found in Cajas N.P. The dwarf forests consist of polylepis (polylepis sp) trees and probably can survive under those extreme conditions, among other things, thanks to their position. Those fairy tale polylepis forests can be encountered at sheltered places at the foot of escarpments and along streams.