384 VOLCANIC EKUPTIONS ON MARTINIQUE AND ST. VINCENT. 



white steam, which has neither sharp, clearlj' defined outlines, nor 

 pufi-like convohitions, and which suggests steam rising* from the hot 

 water of a geyser basin or from the escape pipe of a big ocean steamer." 



The explanation of the occurrence of such a column from a crater 

 of the t3'pe of the one at the summit of Mont Pelee, a sketch of which 

 by Varian is herewith given (fig. 1, PI. II), seems to be that the top 

 of the lava column is well below the bottom of the crater, and that 

 the hot rocks are discharging steam, owing to the contact with them 

 of water percolating in from the crater walls or falling as rain. The 

 generation of steam is a surface phenomena, and due essentially to the 

 same cause as the escape of steam from hot del^ris ejected by a volcano 

 and accumulating in valleys, etc. The notable feature is the absence 

 of convolutions and more or less individualized fleece-like masses in 

 the ascending column, such as are produced ])y small steam explosions 

 from li(juid lava, as is frequently the case at Vesuvius. 



'■'2. The vapor of modei-ate activity: A cohinui of greater density 

 and somewhat darker color, which rolls and unfolds a little as it rises, 

 and looks like steam mixed with brownish or yellowish smoke from 

 the chimney of a manufactory." 



This stage may reasonabl}' be supposed to indicate conditions simi- 

 lar to those mentioned in the first instance, but more intense. A con- 

 siderable volume of water gaining access to the deep funnel-shaped 

 crater might not be vaporized before descending to the sununit of the 

 column of liquid or but partiallv congealed column of rock Avithin the 

 conduit, and energetic explosions result. The steam coknnns indica- 

 tive of moderate activity thus correspond with the columns produced 

 by the maximum explosions of pseudo-craters. The inner slope of the 

 crater of Mont Pelee is precipitous, and, as several observers have 

 reported, portions of its walls overhanging. The fall of blocks of 

 rocks from the crater walls would no doubt cause a conspicuous col- 

 umn of dust-laden steam to ascend. 



'■'3. The vapor of dangerous activity: A sharply defined dark- 

 yellow column of what a])pears to be li(|uid mud, which l)()ils out of 

 the volcano in huge, rounded masses, swelling and evolving in inunense 

 convolutions as it rises — one gigantic nuid bubble breaking u}) out of 

 another in tui"n — until over the crater there stands a solid opacjue })il- 

 lar of ))oiling, unfolding, evolving mud vapor 500 feet in diameter 

 and eight or ten thousand feet in height." 



'^riie a})pearanc(^ of the volcano duiMiig the stage here descril)ed is 

 illustrated by sketch by Varian, forming PI. IV, and by fig. 1, PI. MI. 

 When such a debris-charged steam column rises from a crater there 

 is no (pu^stion as to the presence of a conduit leading down deep into 

 the earth. The pseudo-craters never reach such intensity. 



"•4. The vapor of great eruptions: A straight-sided shaft of very 

 black smoke (dust-charged steam), which shoots up out of the crater 



t 



