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Structure

1. Introduction	8. Radiocarbon Dating Table
2. Site Table	9. Historical Dating Table
3. Profile Table	10. Geochemical Table
4. Context Table	11. EPMA Session Table
5. Tephra Layer Table	12. Eruption Table
6. Tephra Subunit Table	13. Phase Table
7. Physical Property Table	14. Reference Table

1. Introduction

This database was developed in the Department of Geography at the University of Edinburgh. The pages accessed enable complex searches of the database to be carried out. Both published and unpublished data on tephra deposits and their source volcanoes are available. Originally the database only contained data on tephra layers erupted from Icelandic volcanoes; the database now also contains data on some tephra layers found in central Mexico. The Mexican and Icelandic data is coded separately and searches on each area are carried out indepenantly.

The tables below describe the format of each table in the database and the type of information which will be held in each. Where appropriate the maximum size of a column is shown. Each table actually contains more columns than are shown below, but these are only for controlling the structure of the database and creating links between tables. The column name within each table of the database are listed below in alphabetical order.

2. Site Table

This table holds location data on a site. The site could be a site of an eruption, volcanic centre or profile where a tephra layer occurs.

Column Name	Max. Length	Description
Altitude		The altitude of the site in metres
Area	60 characters	The area/region of a country the site is found in
Country	60 characters	The country the sites is found in
Grid Reference		The grid reference (8 figures) of the site (UK only)
Latitude		The latitude of the site
Longitude		The longitude of the site
Site Name	60 characters	The name of the site
Type Site		Whether the site is a type site for a tephra layer

3. Profile Table

This table hold details about the profile where a tephra layer is found. The could be a core, ditch, archaeological site or even a surface.

Column Name	Max. Length	Description
Profile Name	20 characters	The name of the profile
Total Depth		Total depth of the profile in metres
Type of Profile		The type of profile (Russian core, ditch etc.)
Type Profile		Whether the profile contains a type tephra layer

4. Context Table

This table contains more information about a site or profile.

Column Name	Max. Length	Description
Summary	65.5 K characters	More details about a profile or site.

5. Tephra Layer Table

This table hold details about the name and position of a tephra layer within a profile. Multiple names are available to accommodate the various names a tephra layer can be known as.

Column Name	Max. Length	Description
Bottom Depth		The depth of the base of a tephra layer in a profile I metres
Tephra Name 1	60 characters	Formal name e.g. Hekla 4
Tephra Name 2	60 characters	Regional Name e.g. Glen Garry Tephra
Tephra Name 3	60 characters	Local Name
Tephra Name 4	60 characters	Source Name
Top Depth		The depth of the top of a tephra layer in a profile in metres
Type Tephra		Whether a tephra layer is a type tephra

6. Tephra Subunit Table

This table hold details of the name and position of subunits within a tephra layer. This would only be used in the case of macroscopic tephra layers.

Column Name	Max. Length	Description
Bottom Depth		The depth of the base of a subunit in a profile in metres
Subunit Name 1	60 characters	Formal name
Subunit Name 2	60 characters	Regional Name
Subunit Name 3	60 characters	Local Name
Subunit Name 4	60 characters	Source Name
Top Depth		The depth of the top of a subunit in a profile in metres
Type Tephra		Whether a subunit is a type subunit

7. Physical Property Table

This table hold details of the physical properties of a tephra layers.

Column Name	Max. Length	Description
% between 125-250 µ m		grain size
% between 250-500 µm		grain size
% between 500-1 µm/mm		grain size
% between 63-125 µm		grain size
% greater than 1 mm		grain size
% less than 63 µm		grain size
% Lithic		% of lithics in a tephra layer
% Glass		% of glass shards in a tephra layer
% Minerals		% of minerals in a tephra layer
Aggregate Tephra Colour	30 characters	Hand specimen colour
Concentration	20 characters ?	Concentration of shards per cm3?
Mean grain size		Mean grain size in mm
Median Grain Size		Median grain size in mm
Mineralogy	150 characters	Mineralogy of tephra layer
Morphology	60 characters	The morphology of the glass shards
Qualitative grain size	30 characters	The qualitative grains size, e.g. coarse, fine etc.
RI Mean		The mean refractive index
RI Standard Deviation		The standard deviation of the refractive index to 1 sigma
Rounding	30 characters	The amount of rounding of tephra grains
Shard Colour	20 characters	The colour of the glass shards
Sorting	20 characters	The degree of sorting ?
Tephra Layer Colour	30 characters	The colour of the tephra layer insitu

8. Radiocarbon Dating Table

This table holds details on the radiocarbon dating of tephra layers, profiles and eruptions.

Column Name	Max. Length	Description
Address	200 characters	The address of the radiocarbon laboratory
Bottom Depth		Depth of the base of a sample from a profile in metres
Conv/AMS		Whether a date was by beta counting (radiometric/ Conventional) or AMS
Delta 13C ratio		The measured ratio wrt PDB
Fraction	20 characters	The fraction dated (e.g. humin, humic acid, cellulose, etc.)
Type of material	60 characters	The material dated (e.g. peat, wood etc.)
Radiocarbon date		The mean age in conventional years BP
Sample lab. number	10 characters	(e.g. GU-7115, SRR-5573, UB-3354)
Standard Deviation - 1		Standard deviation of the age measurement to 1 sigma
Top Depth		Depth of the top of a sample from a profile in metres

9. Historical Dating Table

This table hold details on the absolute, historical dating of an eruption or tephra layer

Column Name	Max. Length	Description
Bottom Depth		Depth of the base of a point in a profile in metres where the absolute date is known
End Date		The end date/time of an eruption or tephra fall in years AD/BC
Start Date		The start/time of an eruption or tephra fall in years AD/BC
Top Depth		Depth of the top of a point in a profile in metres where the absolute date is known

10. Geochemical Table

This table holds all of the geochemical data about a volcanic system, eruption or tephra layer. The columns in this table are arranged so that the major elements (wt %) are followed by the trace elements (ppm). Each of the major elements has an extra column which records the standard deviation of a mean.

Column Name	Max. Length	Description
Number of analyses		The number of analyses represented by a mean
Mean		Whether an analysis is a mean
SiO2
SiO2 Std Dev.		Standard deviation of a mean analysis
TiO2
TiO2 Std Dev.		Standard deviation of a mean analysis
Al2O3
Al2O3 Std Dev.		Standard deviation of a mean analysis
Fe2O3
Fe2O3 Std Dev.		Standard deviation of a mean analysis
Fe2O3T		Total iron expressed as Fe2O3
Fe2O3T Std Dev.		Standard deviation of a mean analysis
FeO
FeO Std Dev.		Standard deviation of a mean analysis
FeOT		Total iron expressed as FeO
FeOT Std Dev.		Standard deviation of a mean analysis
MnO
MnO Std Dev.		Standard deviation of a mean analysis
MgO
MgO Std Dev.		Standard deviation of a mean analysis
CaO
CaO Std Dev.		Standard deviation of a mean analysis
Na2O
Na2O Std Dev.		Standard deviation of a mean analysis
K2O
K2O Std Dev.		Standard deviation of a mean analysis
P2O5
P2O5 Std Dev.		Standard deviation of a mean analysis
LOI		Loss on ignition (XRF analyses only)
Total		The total of major elements (in XRF including LOI)
Total Std Dev.		Standard deviation of a mean analysis
Ba
Ce
Cr
Cu
La
Nb
Nd
Ni
Pb
Rb
Se
Sr
Th
V
Y
Zn

11. EPMA Session Table

This table hold details on the type of electron microprobe used for an analysis and the conditions it was operated under.

Column Name	Max. Length	Description
Accelerating Voltage		The accelerating voltage of the beam in kV
Beam Current		The beam current in nA
Correction Programme	20 characters	The correction programme used (e.g. ZAF)
Counts		?
Machine Name	60 characters	The name and make of the machine used
Sample Type	60 characters	The type of sample analysed (e.g. thin section - carbon coated)
Standards	60 characters	The standards used to calibrate the machine
Type		WDS or EDS analysis

12. Eruption Table

This table contains details of an eruption.

Column Name	Max. Length	Description
Eruption Name	60 characters	The name of the eruption
Maximum Column Height		The maximum height of the column in metres
Mean Column Height		The mean height of the column in metres
Summary	65.5 K characters	Summary information about an eruption
VEI		The VEI index of the eruption
Volcano/fissure	100 characters	The name of the volcano/fissure
Volume of Lava DRE		The volume of lava produced - dense rock equivalent (km3)
Volume of Tephra DRE		The volume of tephra produced - dense rock equivalent (km3)
Volume Total DRE		The total volume of the eruption - dense rock equivalent (km3)

13. Phase Table

This table hold details of phases of activity during an eruption.

Column Name	Max. Length	Description
Maximum Column Height		The maximum height of the column in metres
Mean Column Height		The mean height of the column in metres
Phase Name	60 characters	The name of the phase of activity
Summary	65.5 K characters	Summary information about a phase of activity
VEI		The VEI index of the phase of activity
Volume of Lava DRE		The volume of lava produced - dense rock equivalent (km3)
Volume of Tephra DRE		The volume of tephra produced - dense rock equivalent (km3)
Volume Total DRE		The total volume of the eruption - dense rock equivalent (km3)

14. Reference Table

This table hold references on tephrochronology, volcanism and related topics. The references are at present very biased towards Iceland.

Column Name	Max. Length	Description
Address	180 characters	The address of donators of unpublished data
Author	200 characters	The authors of an article or book
Editor	60 characters	The editors of a book
Journal	200 characters	The title of a journal or book
Keywords	200 characters
Name	60 characters	The name of a donator of unpublished data
Page
Publisher	60 characters	The publisher of a book
Summary	65.5 K characters	A summary of the reference
Title	240 characters	The title of an article
Volume		The volume of a journal
Year		The year of publication