Weathering of basaltic rock and clay mineral formation in Leyte, Philippines

Issue Date

9-2007

Abstract

The study evaluated the weathering of basalt by determining gain and loss of elements, stream water composition, weathering indices and clay mineral formation in the soil derived from volcanic rock under humid tropical conditions in Leyte, Philippines. The study site is located in a secondary forest at an elevation of 100 m above sea level with an average annual rainfall of 2700 mm and an average temperature of 28 °C. The weathering profile in the site is about 4 m deep, heavy clay, acidic and yellowish red soil classified as Alisol in the World Reference Base or Ultisol in terms of Soil Taxonomy. Results revealed intensive loss of elements, particularly the basic cations Ca, Mg, K and Na and, to a lesser extent, Si. There was accumulation of Al, Fe, C and H2O in the weathered soil. The extent of weathering, as indicated by the loss of elements based on total elemental composition of fresh rock and weathered product (saprolite and soil), is closely related to the cation composition of the water from the stream draining the site. Relative rates of loss of bases and silica revealed the sequence Ca>K>Na>Mg»Si for the soil, and the sequence Ca>Na ≥ Mg>K for the stream water. The ratio Na/(Na+Ca) in stream water indicated that the major source of cations in the stream is rock weathering. The intensive basalt weathering resulted in the formation and abundance of kaolinite and halloysite clay minerals as well as the iron oxide goethite in the strongly weathered soil. The idea that weathering moves to a system composed of SiO2, Al2O3, Fe2O3 and H2O appears to be supported by the results of the study.

Source or Periodical Title

Philippine Agricultural Scientist, The (Formerly: The Philippine Agriculturist)

ISSN

0031-7454

Volume

90

Issue

3

Page

222-230

Document Type

Article

College

College of Agriculture and Food Science (CAFS)

Frequency

quarterly

Physical Description

maps; graphs; tables; references

Language

English

Subject

basalt weathering, clay materials, strongly weathered tropical soil, gain or loss of elements, stream water composition

En – AGROVOC descriptors

BASALT; CLAY MINERALS; TROPICAL SOILS; WEATHERING; LOSSES FROM SOIL; ELEMENTAL ANALYSIS; SOIL PH; SOIL CHEMICOPHYSICAL PROPERTIES

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