Active Cone Mackenney
Cono activo Mackenney.
Photo: Marvin Grijalva Photography
TYPE OF ACTIVITY: Composite stratovolcano
TYPE OF ERUPTION: Strombolian.
INDEX VOLCANIC EXPLOSIVITY: 4 (Year 1,775).
CONTENTS DANGER: 13 (According to Yokoyama et al., 1984).
LOCATION: 40 km. To the SSW of the City of Guatemala, in the town of San Vicente Pacaya, Escuintla.
GEOGRAPHIC POSITION (Active cone):
14 Degrees. 23 Minutes Latitude N 90 Degrees 36.2 Minutes Length W
HEIGHT: 2,562.08 masl,
RELATIVE HEIGHT: 1,000 meters.
FORM AND STRUCTURE
The complex constituting the Pacaya volcanic complex is a relatively complicated, heavily fractured and faulted massif comprising several structures including an ancient stratovolcano, lava
domes and the modern compound volcano. The latter is the one that has caused the eruptions in recent times.
It is located in the southern part of an old volcanic
caldera, whose main depression is currently occupied by Lake Amatitlán related to the formation of the current volcanic complex.
The lake of Amatitlán
was originated by tectonic subsidence that gave rise to the reservoir of the waters of small rivers and is limited by several semicircular faults whose main directions, both in the north flank of the complex Pacaya volcanic like in the lake proper, run in
bearings NS and NE-SW, and also some WE fractures, to WNW-ESE.
The former stratovolcano, occupying the center of the volcanic complex, has smooth slopes partially
eroded and extends to near San Vicente Pacaya.
Its activity possibly began 23,000 years ago, at the site of the Calderas Lagoon. Several investigators indicate
the existence of two explosive craters around this lagoon, one to the west with about 250 m in diameter and the other to the east with about 450 m. The eminent geologist and vulcanologist Seebach believes that these craters were in activity in the year 1,560
but geologists Dolfus and Montserrat think that during that period of activity it is possible that the northwestern cone have formed.
In the southern margin
of Lake Amatitlán and in the surroundings of the present compound volcano, there are domes that have an acid and intermediate composition, and that are reflected in the topography as rounded hills.
The so-called "modern compound volcano" is a stratovolcano with a horseshoe-shaped caldera that opens to the southwest, and is located in the southwest part of the volcanic complex. Inside this boiler, there is a cone formed
later, called Mackenny cone, which has been changing its form since 1961 by a frequent effusive and explosive volcanism. This activity has generated frequent lava flows that cover the bottom of the caldera and extend mainly to the south. At the northern edge
of the caldera, there is a small parasitic cone, called Cerro Chino.
From the year 1961 to the present time the MacKenney cone has produced a series of lava flows that have been deposited
in the south-southwest flank and that at present have been object of study and that form present part of the structure of the new compound volcano .