Introduction
During the past century, numerous observers have described the violent ejection of large
blocks and bombs from volcanoes during volcanic explosions. Minakami (1942) mapped the
locations of blocks ejected from Asama Volcano during explosions in 1937. He developed a
mathematical expression relating initial velocity and trajectory angle of ejected blocks to the
ejection distance, taking into account air drag and assuming a constant drag coefficient. In the
late 1950’s, Gorshkov (1959) estimated ejection velocities at Bezymianny volcano during its
sector-collapse eruption. Wilson (1972) developed the first mathematical algorithm for ballistic
trajectories in the volcanological literature (earlier ones had been available for military
applications) that considered variations in drag coefficient with Reynolds number. Fagents and
Wilson (1993) advanced the method of Wilson (1972) by considering the effect of reduced drag
near the vent. From the 1970’s through the 1990’s other papers, too numerous to mention, have
estimated volcanic ejection velocities from ballistic blocks.
Since the early 1990’s there has been a decrease in the number of published papers that
quantify ejection velocities from ballistic trajectories. This decrease has resulted in part from the
appreciation that ejection velocities cannot be uniquely determined by ejection distance due to
uncertainties in initial trajectory angle and drag force. On the other hand, the decrease in usage
has coincided with an increase in the ease with which ballistic calculations can be made, due to
the vast improvement in computer power and in the user-friendliness of computers. During the
1970’s, only volcanologists with mathematical acumen or those who could collaborate with
applied mathematicians were able to make such estimates. With 21st century computer power,
ballistic computation should be available to anyone as a back-of-the-envelope indicator of
explosive power; the only factor preventing such usage is the lack of a user-friendly computer
program.
In this paper, I describe a program that can be used for quick ballistics calculations. The
program, Eject!, was written in Microsoft Visual Basic® and operates on any personal computer
running Microsoft® Windows 95 or later.
Instructions on installing Eject! version 1.4
- Copy the file "eject_1-4.zip" to the hard drive of your Windows-based computer
- Unzip the files in "eject_1-4.zip"
- Double-click on the file "setup.exe". This will install the software on your computer.
- Once it is installed, go to the "start" button, the to "programs." You will see the program in your program list.
|
Part or all of this report is presented in Portable Document Format (PDF). For best results viewing and printing PDF documents, it is recommended that you download the documents to your computer and open them with Adobe Reader. PDF documents opened from your browser may not display or print as intended. Download the latest version of Adobe Reader, free of charge.
|