Yoshihisa Hiroki

This paper explains how to draw a graph of flow velocity changes from columnar section data using the Hjulström diagram. The procedure is as follows:(1) recognition of erosional and/or depositional events within a columnar section,(2) reading flow velocity for each event using the Hjulström diagram,(3) plotting the readings, and (4) drawing a curve of flow velocity changes. In the procedure, sedimentological knowledge is required, especially for the recognition of erosional events, but the changes in flow velocity can be drawn only with depositional events, which are easy to recognize in columnar sections.

Experiments on strata formation using a donut-like water tank were proposed for a lesson on strata in the 6th grade of elementary school. Six experiments were conducted with different detritus sediments being put into the water: Experiment A: granules, fine sand, and mud; Experiment B: granules, very fine sand, and mud; Experiment C: granules and fine sand; Experiment D: granules and very fine sand; Experiment E: fine sand and mud; and Experiment F: very fine sand and mud. In Experiments D and E, strata with obvious bed contacts were formed. On the other hand, the bed contacts were relatively unclear in Experiments A, B, and C. In Experiment F, flame structures were formed at the bases of the sand beds. This suggests that Experiments D and E are suitable as elementary school lessons on strata formation. The equipment is light in weight and the experiments are easy to prepare.

Four experiments on strata formation in stream water using a straight flume were carried out with different detritus sediments: Experiment A (granules and fine sand), Experiment B (granules and very fine sand), Experiment C (fine sand and mud), and Experiment D (very fine sand and mud). In Experiments A and B, almost parallel interbeds of granules and sand were formed. In Experiment C, the mud was deposited in a lens-like formation. In Experiment D, bed boundaries were of a wavy shape, and flame structures were formed at the bed boundary of the sand and mud. Thus, it was concluded that Experiments A and B form parallel strata that are suitable to be demonstrated in a lesson on strata in the 6th grade of elementary school.

This paper discusses answers to the question “Are Grains of 2 mm in Diameter Gravel or Sand?” Geologists and sedimentologists examine the grain sizes of sediments and sedimentary rocks to classify them into gravel (conglomerates), sand (sandstone), or mud (mudstone), and it would not be a problem as to whether grains of 2 mm in diameter should be called gravel or sand. Grains are usually irregular in shape, and grains of just 2 mm in diameter with a perfectly spherical do not exist in nature. Grains around 2 mm in diameter can be classified into: gravel larger than 2 mm in diameter, or sand smaller than 2 mm in diameter in geological and sedimentological studies.

This study investigated the usage of north symbols on maps in signboards, newspaper flyers, and textbooks of elementary, junior high, and high schools, and assessed the recognition of north symbols by university students as well as the effect of elementary, junior high, and high-school lessons on such recognition. Almost all students recognized symbols similar to the magnetic north symbol used by the Geological Survey of Japan as the appropriate sign for north, but very few students (around 5%) were aware that the iconic representations of true north and magnetic north were distinct from each other. North symbols used in signboards and newspaper flyers were varied. Students have not acquired accurate knowledge with regard to the differences in north symbols through lessons imparted to them in elementary, junior high, and high schools, suggesting that there is a need to improve instruction on the subject. Students specializing in geology should be taught the correct symbols denoting the notion of north.

This paper looks at experiments on strata formation carried out in elementary schools as to whether the strata formed in the experiments simulate those as detailed in science textbooks and in government curriculum guidelines. Strata, as taught in the textbooks and in the guidelines, are defined as “detritus sediment strata comprising gravel, sand, and mud deposited in stream water such as a river.” However, experiments conducted in elementary schools simulate the formation of strata by sediment gravity flow or by sorting during the settling of sediment grains. Therefore, the experiments are not suitable as elementary school lessons on strata formation. This paper also found that no suitable experiments for such lessons are described in published academic papers. Thus, suitable experiments need to be developed.

This paper attempts to explain the Hjulström’s diagram, which is an important tool to understanding the formation of detritus sediment strata associated with stream water. Although the Hjulström’s diagram was first introduced around 80 years ago, it is still useful when attempting to understand the manner in which detritus beds form deposits in water. The diagram also illustrates the relationship between the grain size of sediments and the flow velocities at the time of deposition and erosion. Strata are formed due to the deposition of beds with differing grain sizes during cyclic flow velocity changes. Each depositional environment coincides with a specific hydraulic energy at which the fluctuation in flow velocity exhibits a specific range; therefore, beds having specific grain sizes are deposited. Coarse-grained sediments are generally deposited in environments with high hydraulic energy, while fine-grained sediments are more general in environments with low hydraulic energy.

We developed a manual for rock identification for high-school students and a lesson plan to improve their ability in rock identification in the subject of Chigaku-kiso. The manual deals with 14 kinds of rock. Students were taught the features and formation of igneous rocks, sedimentary rocks, and metamorphic rocks in the first three classes, and then the procedures to identify rocks by using the manual were taught in the fourth class. The percentages of correct answer in tests on rock identification increased through the lessons, confirming the effectiveness of the lessons and the manual. The students' confidence in their ability to identify rocks also increased after the fourth class. Of the 85 students, 90.6% said that the manual was easy to use.

We examined the meanings of “stone”, “rock”, “mud”, “clay”, and “soil” when used as everyday words and how these everyday words can be confused with the scientific terms taught in elementary and junior high schools such as “rock”, “mineral”, “gravel”, “sand”, “mud”, and “clay”, and discussed the differences in meanings between the everyday words and the scientific words. The everyday words are defined based on the usages of materials in our life. On the other hand, the scientific words are defined based on the features of the components of materials.

The purpose of this paper is to report on mistaken descriptions made in reports on a field exercise by university students taking a school teacher course, regarding the depositional environments of gravel beds, and to discuss the causes of the mistakes. Four cases of the mistakes were found. Case 1: mistaking the rock names of gravel as the name of the beds. Case 2: mistaking the depositional environments of gravel beds with those of the host rocks of gravel. Case 3: mistaking the current environments as the depositional environments of the gravel beds. Case 4: unclear and inappropriate usages of logic in the reports. These four mistakes were most likely caused by an inadequate understanding of the processes of gravel bed formation (Cases 1, 2, and 3); by low awareness regarding the use of accurate words and phrasing (Case 1); and by low awareness regarding writing logical sentences (Case 4). In particular, the percentage of the students who made the mistake shown in Case 2 was 47.3%, showing that their understanding was insufficient regarding the processes of gravel bed formation.

Three experiments were conducted using ice balls to model the effects of the compaction, pressure solution, and cementation of sand grains during lithification. In experiment A, two ice balls were stacked together in a plastic pipe, which was then placed in a freezer at temperatures ranging from −14.5°C to −19.6°C. In Experiment B, the same conditions were used, but stainless-steel nuts and bolts weighing 890 g were placed over the stacked ice balls to simulate compaction. After one month, the ice balls in both experiments were bonded together. Thin section observations of the bonded ice balls from Experiment A showed that the contacts between ice balls resembled the long contacts of sand grains formed during pressure solution. In Experiment C, two ice balls were placed together in a plastic pipe filled with warm air (33.0°C and 46% relative humidity), which was then sealed with a plastic covering and placed in a freezer at temperatures ranging from −17.8°C to −20.0°C. Two months later, these ice balls were cemented together by fine interstitial ice crystals, indicating the formation of an ice cement between ice balls. These results suggest that ice ball experiments can be used to model the processes of clastic lithification by pressure solution and interstitial cementation, thus providing a better understanding of the consolidation of sands.

The purpose of this research is to assess knowledge of the textures of igneous rocks and the ability to identify hand specimens of igneous rocks among high-school students. Ninety students were asked about textures and rock types for two sketches of igneous rocks, namely the equigranular texture of plutonic rock and the porphyritic texture of volcanic rock. Among the students tested, 98.9% of them answered correctly for rock types and 84.4% of them answered correctly for texture names. In addition, they were asked about rock types, namely whether plutonic or volcanic for a hand specimen of granite (polished or unpolished) or for a photograph of granite. Among 30 students, 53.3% answered correctly for polished granite, 33.3% for unpolished granite, and 40.0% for the photograph of granite. These findings exhibited that students successfully acquired knowledge of the textures of igneous rocks but that this knowledge did not lead to the acquisition of the ability to identify hand specimens of igneous rocks. It is difficult for students to recognize textures in hand specimens. Thus, the opportunity to observe hand specimens of igneous rocks should be increased in secondary schools, and instruction methods to improve students' ability to identify igneous rocks should be developed.

Students' satisfaction to the subject `Kadai-Kenkyu (theme research)' and primary factors affecting their satisfaction and continuation of further research were examined in a high school, which was designated as a 'Super Science High School'. The results of analysis exhibited that the following instructions were effective to enhance students' satisfaction to the subject. (1) The instruction that allows a student to think that a research obtained excellent results. (2) The instruction that allows a student to think that a research theme was what he/she wished. (3) The instruction that allows a student to think that teacher's instruction was good. The results also exhibited that the following instructions were effective to enhance students' motivation to continue further researches. (1) The instruction that allows a student to think that a research theme was what he/she wished. (2) The instruction that allows a student to think that a research enhanced his/her interest in science and science technology. (3) The instruction that allows a student to think that the theme research was important subject for him/her. Based on these results, an instruction model was developed for theme research to enhance students' satisfaction and motivation to continue researches. The model includes explanations of the importance of the subject, of the perspective of a research theme and of the academic significance of research results in addition to the general instruction for scientific research.

The purposes of this research are to exhibit understandings on the origin of sands by elementary school, lower secondary school, and university students, and to discuss problems on the lesson of rock weathering. The fifth-grade students of elementary school have a variety of ideas on the origin of sands. After the lesson of stream water, many students explain the origin of sands by two models: erosion model (29.9%) or collision model (25.6%), rather than weathering model (0%). The percentage of the students who prefer the erosion model increases to 52.5% after the lesson of rock weathering and erosion in lower secondary school. The percentage of the students who prefer the weathering model is only 8.8%. The results exhibit that the erosion model and the collision model are acquired by the lesson of stream water in elementary school and that the erosion model is strengthened by the lesson of erosion in lower secondary school. Introduction of a lesson of soil may help secondary school students understand the sand-grain formation by rock weathering.

Although sandy foreshore facies are generally characterized by parallel lamination, wavy lamination is predominant in the mixed sand and gravel foreshore facies of the Pleistocene Hosoya Sandstone, which crops out along the Pacific coast of the Atsumi Peninsula, Aichi, central Japan. The foreshore facies consists of three sedimentary subfacies; interbeds of gravel and parallel laminated sand of the lower foreshore facies, parallel laminated fine to medium sand beds containing scattered pebbles and cobbles of the middle foreshore facies, and wavy laminated fine to medium sand beds containing scattered pebbles and cobbles of the upper foreshore facies. A lack of erosional surfaces in the middle foreshore facies indicates the continuous accumulation of sand in flat beds under upper plane bed flow. The wavy laminated sands of the upper foreshore facies exhibit erosional surfaces indicative of repeated deposition and erosion. The erosional surfaces are undulatory, with depressions (10 cm wide and 3 cm deep) that contain scattered pebbles and cobbles. These depressions reflect backwash erosion of sand around and below the pebbles and cobbles. Sand draping over the undulating erosional surfaces forms the wavy lamination. The wavy laminated sand with scattered pebbles and cobbles is a key facies of an upper foreshore or swash zone, and is a good sea-level marker.

Nowadays, the depression of curiosity about science of young Japanese people markedly increases in Japan. The experiments in school, one of the way for making a sense for science curiosity, are very important. However, teachers in Japanese schools, especially graduated at literature courses, tend to hesitate for teaching the scientific experiments. This fact may enhance a depression of the scientific curiosity. The present study, therefore, reports on our first trial experimental lectures of science open for 4th grade students in the literature courses in our university.

Stratigraphic controls on the formation and distribution of gas hydrates were examined for sediments from a BH-1 well drilled in the landward slope of the Nankai Trough, approximately 60 km off Omaezaki, Japan. Three lithologic units were recognized in the 250 m-thick sequence of sediments: Unit 1 (0-70 mbsf) consists of calcareous silt and clay with thin volcanic ash layers, Unit 2 (70-150 mbsf) consists of calcareous silt and clay with volcanic ash and thin sand layers, and Unit 3 (150-250 mbsf) consists of weakly consolidated calcareous silt and clay with thick and frequent sand layers. Soupy structures and gas bubbles in the sediments indicate the presence of two hydrate zones between 40 and 130 mbsf and below 195 mbsf. Nannofossil biostratigraphy and magnetostratigraphy indicate that the sequence recovered at the BH-1 well is mostly continuous and represents sediments deposited from 0 to 1.5 Ma. Calculation of the sedimentation rate reveals a condensed section between 65 and 90 mbsf. The inferred distribution of gas hydrates in the BH-1 well appears to be strongly controlled by the stratigraphy and lithology of the sediments. Thick, gently inclined sand layers in Unit 3 provide a conduit for the migration of gases from deeper regions, and are considered responsible for the formation of the hydrate zone below 195 mbsf. At shallower levels, thin, gently inclined sand layers are also considered to allow for the migration of gases, leading to the formation of the upper hydrate zone between 40 and 130 mbsf. The overlying sub-horizontal silt and clay of the condensed section, truncating the underlying gently inclined sand and silt/clay layers, may provide an effective trap for gases supplied through the sand layers, further contributing to hydrate formation in the upper hydrate zone.