  Shape analyses of tephra grains result in understanding eruption mechanism of
volcanoes. However, we have to define and select parameter set such as
convexity for the precise discrimination of tephra grains. Selection of the
best parameter set for the recognition of tephra shapes is complicated.
Actually, many shape parameters have been suggested. Recently, neural network
has made a great success in the field of machine learning. Convolutional neural
network can recognize the shape of images without human bias and shape
parameters. We applied the simple convolutional neural network developed for
the handwritten digits to the recognition of tephra shapes. The network was
trained by Morphologi tephra images, and it can recognize the tephra shapes
with approximately 90% of accuracy.
