Unless you want to replace every article link in the encyclopaedia with a little footnote explaining what the term means, then your stance doesn't make sense.  Footnotes which take readers away from the text of the article are not very helpful and there is no support in the MOS for the use of footnotes in this way.
If you think that people generally won't understand what a lahar is and cannot simply click on the link to an article, then a short explanation of the geological activity that led to the disaster would be an infinitely better means of dealing with that.  At the moment it's only briefly mentioned in the lead. 201.215.187.159