٨Research Trends and Results

Simple method of Identifying Sources ofSupply of Beach Sand by ChemicalAnalysis of Sand Grains


SUWA Yoshio, HeadWATANABE Kunihiro, Researcher
Coast Division, River Department

Research Trends and Results(Key words) Beach sand, sand supply, mineral analysis, whole-rock analysis 
1. Where did this sand come from?
“Tiny particles were discovered in the capsule!”
The world swung from joy to despair over a few
grains of sand carried from the Itokawa Asteroid bythe Hayabusa spacecraft. The question, “where didthis sand come from?” is an important challenge for
the Coast Division.
 Beach sand is maintained by a balance between
sand washed away by the action of waves and windand newly supplied sand. At locations whereinsufficient sand is supplied, coastline erosion occurs,
exposing the hinterland to danger, so identifying thesources of sand is indispensable for coastline
management.
The Coast Division is working cooperatively with
Tokyo City University to develop methods of identifying
the supply sources of sand. This report introduces
research carried out along Kujukurihama Beach.

2. How is the source of supply of sand identified?
There are cases where coastal sand consists of avariety of different minerals, permitting researchers tohypothesize the sources of its supply by examining its
mineral constituents under a microscope. But
identifying minerals requires experience, andidentifying minerals in more than 100 grains in asingle sample is a labor-intensive task. One method of
more easily identifying the constituents of sand is touse fluorescent X ray analysis to perform whole-rockanalysis which quantifies the 10 major elements and 9trace elements found in all sand.
Arakawa River

Tonegawa River

3. Differences of sand supply sources revealed bychemical analysis
The results of analysis of sand and rock sampledfrom Kujukurihama Beach, the nearby coastline,
inflowing rivers, and sea cliffs (Fig. 1) confirm thatthe quantities of Nb in the minerals (Nb/TiO2) arecompletely different on the coastline north of theTokawa Fishing Port and on Kujukurihama Beach,with Byobugaura as the northern boundary (Fig. 2).
Most of the Nb/TiO2 on Kujukurihama Beach isalmost equal to that at Byobugaura, and there are also
points with low Nb/TiO2 on Chojagahama Beach at
the mouth of the Isumikawa River, suggesting thatsand is also supplied from south of Cape Taito-misaki.
According to the results of analysis of other elements,
origins vary according to minerals, and pyroxene on
Kujukurihama Beach for example, originated in thesame Kanto Loam as that on the Shonan Coast.
This reveals that it is possible to clarify differencesin the origins of sand on coastlines by examining theirchemical composition. In the future, more sandsamples will be obtained from the hinterland andinflowing rivers, bringing us closer to finding theorigins of the sand on Kujukurihama Beach.
North from the Tokawa Fishing Harbor
Kujukurihma Beach
Byobugaura
Chojagahama Beach

North from the Tokawa
Fishing HarborSiO2(wt%)Figure 2. Example of the Results of Whole-rockAnalysis of Coastline Sand

Byobugaura

Sagami River

Tokawa Fishing Harbor
Kujukurihama Beach
Cape Taito-misaki
Isumikawa River

Shonan CoastFigure 1. Coast where Whole-rock Analysis of Sand
was Performed

[Source]
A. Ishii, H. Hagiya, K. Watanabe (2010): Study of theorigin of beach sediment based on the chemicalcomposition of beach sand on the Kujukuri Coast,
Annual Journal of Civil Engineering in the Ocean,JSCE, Vol. 26, 1125-1130㩷
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