An ASTER image over Heard for 29 February 2007 (figure 11) was found by Matt Patrick in which two thermal anomalies are shown, separated by ~ 300 m. The anomaly to the SE appeared to be a new feature, representing either a distinct vent or a hot distal portion of an active flow from the main vent. There are no anomalous shortwave pixels between the two anomalies as one might expect for an active lava surface, but the flow may be channeled underground between the anomalies. The total lack of anomalous pixels in the region between the two anomalies, however, caused Patrick to suspect that this is a distinct vent. If this is a distinct vent, it would be the first clear illustration of multiple vents at Heard. None of the previous images Patrick has studied covering the last 6 years (including the 8 December 2006 image, also using Band 9-3-1 color mapping, shown in figure 12) showed indications of a secondary anomaly.

Figure 11. An ASTER Band 9-3-1 RGB composite image of Heard for 29 February 2007, with the shortwave infrared band 9 mapped to red, indicating high temperatures. Two distinct anomalies near the summit of Mawson Peak are shown. The W-most anomaly is at the location of previous anomalies, which appear to be the summit crater (lava lake), while the anomaly 300 m SE is a new feature. Courtesy Matt Patrick.

Figure 12. An ASTER Band 9-3-1 RGB composite image of Heard for 8 December 2006, with the shortwave infrared band 9 mapped to red, indicating high temperatures. One distinct anomaly near the summit of Mawson Peak is shown. Courtesy Matt Patrick.

MODIS satellite data also revealed thermal anomalies on 24 different days between 27 December 2006 and 6 April 2007 (table 3).

Table 3. Thermal anomalies at Heard from mid-December 2006 to early April 2007 from MODIS satellites. Continued from table in BGVN 31:05. Courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP) Hot Spots System.

Geological Summary. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben because of its extensive ice cover. The active Mawson Peak forms the island's high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: Hawai'i Institute of Geophysics and Planetology (HIGP) Hot Spots System, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Matthew Patrick, Dept. of Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA.